but I have lighted upon other mens thoughts in some things and others writting on this same subject who perhaps are my Antipodes may fall upon mine My Antagonists affirm they are able to deduce all my Theorems and the events of all my Experiments from the grounds of Archimedes and Stevinus If they take not their word again I hope they will do it for now I put them to it And though they should which I am not affraid they shall do in haste yet they must prove next that these Theorems and Conclusions so deduced are not new which all their Logick will not prove But what if we do more say they even overthrow many of all your Aerostatical and Hydrostatical Experiments in this and in your last Peice I give you liberty and for your hire a Guiny for each Theorem or Experiment you are able to ransack in either of the two Books though they come near to an hundred But ye must oblige your selves my Masters to do it with Reason laying aside your Sophistry and Canina eloquentia And this I offer Reader that I may reduce them to a better humour and encourage them to leave off flyting and only use reason Neither must they be like the Wasp that only lights upon the sore place But if they love to kindle any more fire they will find me proof against it If it burn them it shall not heat me Nevertheless if they love to juik under deck like Green-horns having no courage in themselves or confidence in their cause they must excuse me if at last I write their names upon a Ticket and bring them above deck This is all I have to say at present Reader and I bid thee farewell ERRATA Pag. 22. lin 8. for weight read benâ—il Pag. 185. lin 24. for E H read F H. Pag. 235. lin 24. for 500. read 5000. Pag. 307. lin 26. read promoting Pag. 313. lin 22. read reflection Ibid. lin 25. read elaborarint Pag. 317. lin 2. read magna Note that in placing the Figures the 12 that should have the fourth place in the third Plate hath the first place in the fourth Contents of the EXPERIMENTS THe first second and third Experiment touching the rising and falling down of Water in Tubs of different sizes Pag. 37. 41. 44. The fourth is a Hydrostatical Experiment shewing the Reason why the Mercurial Cylinder rises and falls in the Torricellian Experiment as it is carried up or down thorow the Air. pag. 46. 50 The fifth shewing the reason why the Mercurial Cylinder rises and falls in the Baroscope as the Pipe is reclined and erected p. 51 The sixth touching the suspension of Liquors in Pipes either closs or open above not only of Water by Water but of Water by Air. pag. 55 c. The seventh touching the Cause of the suspension and keeping up of Water in Weather-glasses pag. 59. The eighth touching the reason why a Stone weighs less in Water than in Air. pag. 71. c. The ninth touching the reason why under a Water 34 foot deep the hight of the Mercury in the Baroscope is 58 inches pag. 77. c. The tenth touching the reason why a man gripping with his fingers the Torricellian Tub seems to find the weight of the Liquor within and yet finds it not pag. 82. c. The eleventh touching the counterpoising of Mercury in Glass-pipes under-under-water by the help of a Ballance above adduced to prove that a heavy Body weighs as much in Water as in Air. pag. 86. The difficulty answered pag. 87. c. The twelfth touching the reason why a Cylinder of Brass may be suspended by a Surface of Water before it touch the bottom that 's 100 foot deep pag. 101. c. The thirteenth is touching two plain heavy Bodies suspended under a Water 34 foot deep pag. 109 Doctor Mores Argument against the Pressure of the Air answered pag. 117 The fourteenth touching the counterpoising of Mercury with Water of Mercury with Air and Water whence some notable Phenomena appear pag. 120. c. The fifteenth touching an Experiment tried in a Water 72 foot deep pag. 127. c. The sixteenth touching the reason why the different wideness of Tubs makes no alteration in the hight of the Liquors suspended in them pag. 133. The seventeenth a notable trial for proving the Pressure of the Water pag. 137. c. Mr. Boyls Experiment in sufficient pag. 146. The eighteenth touching the Diving-Ark pag. 153. c. The nineteenth touching a Siphon made to work under Water with Mercury by the Pressure thereof as a Siphon operats with Water by the Pressure of the Air. p. 180. The last is for demonstrating the precise and just weight of any Pillar of Air Water or Mercury p. 183. c. Contents of the MISCELLANY OBSERVATIONS Observation 1 Anent the killing of Animals in Coal-sinks by the power of Damps and Ill Air. pag. 197. Observ. 2. Touching the position of Iupiter with the Stars of Gemini Novemb. 24. 1669. p. 201. Observ. 3. For knowing the motion of the Sun or Moon in seconds of time ibid. Observ. 4. Touching an Experiment made on the top of Cheviot p. 207. Observ. 5. Touching the oval-Figure of the Sun at his setting p. 209. Observ. 6. Touching a considerable Thunder with great Lightnings in East-Lothian in Iuly 1670. p. 210. Observ. 7. A method for finding out the true South and North Points p. 212. Observ. 8. Touching the reason why a dead body of a man or beast riseth from the ground of a Water after it hath lien there three or four dayes p. 216. Observ. 9. Is a second Experiment made in a Coal-sink for knowing the power of Damps and Ill-Air p. 217. Observ. 10. An account of Experiments tried with the Air-pump p. 218. Observ. 11. An Experiment made for knowing the reason why a round heavy Body as a Bullet of Iron falls not off a plain Body under motion but lies dead p. 224. Observ. 12. Shewing the reason why a stone demitted from the top of a Ships-Mast under Sail falls directly upon the place it hang over p. 226. Observ. 13. Touching the hight of the Mercury in the Baroscope observed by D. Beal p. 228. Observ. 14. Touching the variation of the Magnetick Needle here p. 228. Observ. 15. Touching the Elevation of the Pole here p. 228. Observ. 16. A second method for finding the Meridian p. 229. Observ. 17. Touching a considerable showre of Hail with Thunder and Rain ibid. Observ. 18. Touching a curious Experiment made lately in Germany for shewing the wonderful force of the Air. p. 230. Observ. 19. Touching some proposals of new Engines for War p. 233. Observ. 20. Touching a sad trial one Mr. Campbel suffered in his Family for many dayes from the Devil p. 238. Observ. 21. Touching a large Horn cut off a Womans head lately p. 248. Observ. 22. Touching the Primum vivens in Animals ibid. Observ. 23. Touching the Aliment and growth of Plants p. 252. And touching the
THEOREM IX In all Fluids there is a twofold weight one Sensible the other Insensible THe first is common to all heavy bodies which we find in Water while we lift a Vessel full of it from the ground The Insensible weight of Water and Air or of any other Fluid can scarcely be discerned by the senses though it be as real as the former because the Pressure is uniform By vertue of the second bodies naturally lighter than Water are driven from the bottom to the top as Cork So a man falling into a deep Water goes presently to the bottom and instantly comes up again Here is a natural effect which cannot want a natural cause and this can be nothing else but the Pressure of the Water by vertue whereof he comes up and yet he finds nothing driving him up or pulling him up Therefore there is in all Fluid bodies an Insensible weight as there is one Sensible seing the man that perhaps weighs seventeen Stone is driven up fifteen or sixteen fathom by it And it must be very considerable and exceed the weight of the man seing it is able to overcome such a weight So are vapours and smoke driven upward by the Insensible weight of the Air and by that same weight do the Clouds swim above us THEOREM X. The Insensible weight of Fluids is only found by sense when the Pressure is not uniform FOr understanding of this Proposition I must suppose somethings that are possible but not practicable Put the case then while a man opens his hand the Air below were removed he would scarce be able to sustain the weight of the Air that rests upon the Palm above or if the Air above were annihilated he would not be able to bear down the weight that presseth upward Or while a Diver is in the bottom of the Sea if it were possible to free any one part of his body from the Pressure of the Water suppose his right arm I doubt not but the blood would spring out in abundance from his finger-ends for the arm being free and the other parts extreamly prest the blood of necessity must be driven from the shoulder downward with foâ—ce which cannot be without considerable pain It is evident also from the application of the Cuppin-glass which being duely applied to a mans skin causeth the Air to press unequally the parts without being more prest than the parts within in which case the unequal Pressure causeth the pain and so is found by sense THEOREM XI A Cylinder of Water or of any other Fluid body loseth of its weight according to its reclination from a Perpendicular position towards an Horizontal or levell scituation FOr understanding of this consider that while a Pipe full of Water stands perpendicular the lowest foot sustains the whole weight of the Water above it but no sooner you begin to recline the Pipe from that Position but assoon the Pressure upon the lowest foot grows less So that if the lowest foot in a perpendicular position sustained the burden of ten feet it cannot sustain above five or six when it is half reclined A certain evidence whereof is this the more a Cyilnder of Water is reclined towards the Horizon or Level it takes the shorter Cylinder of Water to counterpoise it as is evident in Siphons For though the one Leg be sixteen inches long and the other but six yet a Cylinder of Water six inches long will counterpoise a Cylinder of sixteen But this cannot be unless an alteration be made in the Pressure For how is it possible that a Cylinder of Water can sometimes be in aequilibrio with a lesser and sometimes with a greater weight unless the Weight and Pressure of it be sometimes more and sometimes less When I say a Cylinder of Water loseth of its weight by reclination it is to be understood only of the Insensible Weight for the Sensible Weight is unchangeable seing it is alwayes a Pillar of so many inches or feet Now the true reason why the Pressure upon the lowest foot grows less is this the more the Pipe is reclined the more weight of the Cylinder rests upon the sides of the Pipe within by which means the lowest foot is eased of the burthen and is altogether eased when once the Pipe lyes Horizontal THEOREM XII All motion in Fluids is from the unequal Pressure of the Horizontal surface Figure 1. FOr understanding this I must distinguish a twofold motion in Fluids one common another proper by vertue of the first they incline as all other heavy bodies to be at the center of the Earth It is evident in the motion of Rivers which descend from the higher places to the valleys even by vertue of that tendency they have to be at the center By vertue of the second they incline to move every way not only downward but upward hither and thither This sort of motion is peculiar and proper only to Fluids and it is that which is spoken of in this Theorem I say then that all motion in Fluids is from the unequal Pressure of the Horizontal surface For put the case A were more prest then B e. g. with a stone then surely as the part A descends the other part B will ascend and so will C and D rise higher too Suppose next the part A were fred of the Pressure of the Air then surely in the same instant of time would the part A ascend and the parts B C D descend As this Proposition is true in order to the first and visible surface A B C D so it is true in order to the imaginary surface I K L M for put the case the space I were filled with a body naturally heavier then Water as lead or stone then behoved that part of the surface to yeeld it being more prest then the part of the same surface K. Or if the space K were filled with a body naturally lighter then water as Cork then ought the water R to ascend it being less prest then the water N or S. THEOREM XIII A body naturally heavier then Water descends and a body naturally lighter ascends Figure 1. FOr understanding of this let us suppose the quadrat space E to be filled with a piece of Lead or Iron I say then it must go down to I and the reason is because the quadrat foot of Water I is more pressed then the quadrat foot of Water K. To illustrat this let us suppose that each quadrat foot of this Water weighs a pound and that the heavy body existing in E weighs two pound If this be the foot of Water I must yeeld seeing it is more prest then K upon the same account must the Water N yeeld and give way to the Stone seeing it is more prest then R. For according to the twelfth Theorem There cannot be unequal Pressure upon a surface unless motion follow For understanding the second part let us suppose the space R to be filled with a piece of Cork
also for if a Cube of Timber resting in the space T be just the weight of the Water T the imaginary surface O T V is no more prest then if T were Water and so it cannot go downward neither can it go upward seing the under part of the Water R is no more prest up by the Timber T then if the space T were filled with Water If it be said according to this reasoning a Stone may be suspended in a deep Water between the top and the bottom which is absurd I answer such a thing may happen in a very deep Water For put the case a Cube of Lead twelve inches every way were to go down twelve thousand fathom it is probable it would be suspended before it came to the ground For coming to an imaginary surface far down where the Pressure is great a Cube of Water twelve inches thick there may be as heavy even specifically as the Cube of Lead is though the Lead be ten times heavier specifically then any foot of VVater at the top If Water suffer compression of parts by the superiour burden it is more then probable that the second foot of Water burdened with the first hath moe parts in it then are in the first and the third moe then in the second and so forth and consequently that the second is heavier then the first and the third heavier then the second Now if this be why may not that foot of Water that hath sixty thousand foot above it by vertue of this burden be so comprest that in it may be as many parts as may counter-ballance a Cube of Lead twelve inches every way If then that imaginary surface that is sixty thousand foot deep be able to sustain the said foot of VVater which perhaps weighs twenty pound why may it not likewise sustain the Lead that is both of the same dimensions with it and weight Hence it is that the Clouds do swim in the Air by vertue of a counter-ballance And we see which confirms this Doctrine that the thinnest and lightest are alwayes farthest up and the thickest and blackest are alwayes farthest down THEOREM XVII The lower the parts of a Fluid are they are the heavier though all of them be of equal quantity and dimensions Figure 1. THis follows from the former which may appear a Paradox yet it seems to be true for though the Water Q at the bottom be of the same dimensions with the Water E at the top yet it is really heavier which happens as I said from the superiour Pressure It is clear also from this namely the Cube of Timber E which swims upon the surface being thrust down to Q comes up to the top again which could not be unless the Water Q were heavier then the Water E. I suppose the Water E and the Timber E to be exactly of the same specifick weight and consequently the surface of the Timber to ly Horizontal with B C D. Now the reason why the Timber ascends from Q to E is no other then this namely that the one Water is heavier then the other for the under part of the Water P being more prest up with the Timber existing in Q then with the Water Q it self it must yeeld and give way to the ascent for if the Cube of Timber existing in Q were as heavy as the Water Q it self it would no more press upon P or endeavour to be up then the Water Q does THEOREM XVIII A heavy body weighs less in Water then in Air. Figure 1. THis is easily proven from experience for after you have weighed a stone in the Air and finds it two pound and an half take it and suspend it by a threed knit to the scale of a ballance and let it down into the Water and you shall find it half a pound lighter The question then is why doth it lose half a pound of its weight I answer the stone becomes half a pound lighter because the surface of Water on which it rests sustains half a pound of it For put the case a stone were resting in R that weighed two pound and an half in the Air it behoved to weigh but two pound in this Water because the Water T sustains half a pound of it For if this Water T be able to sustain the Water R that weighs half a pound it must be also able to sustain half a pound of the stone seing half a pound of stone is no heavier then half a pound of Water Note that when a heavy body is weighed in Water it becomes so much lighter exactly as is the weight of the Water it thrusts out of its own place THEOREM XIX A heavy body weighs less nigh the bottom of the Water then nigh the top thereof Figure 1. FOr clearing this proposition I must suppose from the 17. Theorem that the lower the parts of Water be they are the heavier though all of them be of equal dimensions If then the lowest foot Q be heavier that is have moe parts in it then the foot N it of necessity follows that a stone suspended in Q must be lighter then while it is suspended in N or I. Because if a stone be lighter in Water then in Air as is said even by as much as is the weight of the bulk of Water that the bulk of the stone expells then surely it must be lighter in the one then in the other place because suspended in Q it expells moe parts of Water then while it is suspended in N or I. For example let us suppose the Water N to weigh eight ounces and the Water Q to weigh nine then must the stone suspended in Q weigh less by an ounce then suspended in N seeing as much is deduced from the weight of the stone as is the weight of the Water it expells but so it is that it thrusts nine ounces of Water out of its own place in Q and but eight in N or I therefore it must be one ounce lighter in the one place then in the other This may be tried with a nice and accurat ballance which will bring us to the knowledge of this namely how much the foot of Water Q is heavier then the Water N or O. THEOREM XX. One part of a Fluid cannot be under compression unless all the parts next adjacent be under the same degree of Pressure Figure 1. THis proposition may be proven by many instances for when the Air of a Wind-gun is reduced to less quantity by the Rammer all the parts are most exactly of the same Bensil So is it in a Bladder full of wind It 's true not only in order to this artificial Pressure but in order to the natural Pressure and Bensil of the Air likewise For the Air within a parlour hath all its parts under the same degree of natural compression so is it with the parts of the Air that are without and immediatly under the weight of the Atmosphere It s evident also in
an equipondium there is no Pressure in them at all For answer consider first that in all counterpoises there are necessarily two things the movens and the motum the thing that moves and the thing that is moved Secondly you must consider the motum to have a ponduâ— or weight in it and the movens to have a potentia or power wherewith it moves that weight Thirdly that as the thing that moves hath a power or force in it self whereby it moves so the thing that is moved hath a power or force in it self whereby it resists the motion Fourthly that sometimes the resistance of the thing moved may exceed the power of the movent as when a Quarrier with a Leaver endeavours to prize up a stone too heavy for him or the power of the movent may exceed the resistance of the weight or both may be of equal power Consider fifthly that as the pondus of the thing moved begins to grow more and more so the power of the movent decreaseth proportionably not absolutely as heat is extinguished in Water by the cold Air when it is removed from the Fire but respectively For example when a man holds a ballance in his hand with six pound in the one scale and but one pound in the other if you add another pound the weight grows more and the power and force of the opposite scale grows less proportionably not absolutely for it still remains six pound but respectively that 's to say six pound is less in respect of four than in respect of five or the resistance of six pound is less two counterpoising it than being counterpoised by one When a third is added the weight grows yet more and consequently the resistance of the opposite scale becomes yet less till by adding the sixth and last pound you augment and encrease the pondus to that same degree of strength that the resistance of the opposite scale is of From these considerations I say the surface of Air F G hath not lost all its Pressure absolutely by raising the Mercury from G to H but only respectively because it still retains 29 degrees of force in it self I say respectively because when the Mercury is raised ten inches the power of the Air which is of 29 degrees of force is less in respect of ten ounce then in respect of five or the power of 29 degrees of force is less being counterpoised by ten ounce than being counterpoised only by five And when it is raised 20 it is yet less in this respect than in respect of ten And when it has raised the Mercury to the greatest altitude H it may be said to have lost all its Pressure seing it is not able by vertue of a counterpoise to do any more Even as six pound in this scale may be said to have lost all its resistance and weight by putting in the other scale first one pound next two pound and then three pound till the last be put in at which time it hath no more resistance Though this be yet it still remains six pound Even so the Air F G still remains of the same force and power while it suspends the Mercury G H that it was of before Likewise the Pillar A B cannot be said to have lost all its pressure absolutely by falling down from A to C but only respectively because the said Pillar C B is still 29 ounce weight I say respectively because in falling down ten inches or in losing ten ounce the weight that 's now but 48 is less in respect of 29 than while it was 58. It is yet less when it hath fallen down other ten because being now but 38 it must be yet less in respect of 29 than 48. And when it hath fallen down to C 29 it may be said to have lost all its weight because it can do no more having respectively lost all its Pressure From what is said we see a clear ground to distinguish in Fluids a pondus and a potentia Secondly that the potentia may sometimes exceed the pondus and contrariwise the pondus may exceed the potentia Thirdly that inequality of weight between the pondus and the potentia is the cause of motion of Fluids Fourthly that the motion never ceaseth till the pondus and the potentia become of equal force This conclusion is not so universal as the rest because the motion may sometimes cease before this be For example when the Air is pâ—â—â—â—ing Mercury up thorow a Tub shorter then 29 inches the motion ends before there be a perfect counterpoise for 20 or 15 inches of Mercury can never counterballance the force and power of the Air. In such a case then there is an unequal Pressure the Air pressing the Mercury more than the Mercury doth the Air. EXPERIMENT VIII Figure 12. TAke the Vessel A B C D and fill it with Water as high as H I. Take next a Cylinder of stone F G and drowning the half of it among the Water suspend it with a chord to the beam N O with a ring at E. Now in this case though the stone do not touch the bottom of the Vessel yet the Water becomes heavier than before For discovering the true reason of this I suppose first the weight of the Water before the stone be drowâ—ed to be 40 pound I suppose next that after the stone is drowned the said Water to weigh 50 pound And lastly the stone to weigh 60 pound I say then the Water must be 10 pound heavier than before because it supports 10 pound of the stone 'T is certain the beam is less burdened by 10 pound than before If this be then surely the Water must sustain it It were great temerity and rashness to averr that neither the Beam nor the Water sustains it which is really to say it is sustained by nothing It cannot be said without ignorance that 10 pound of the stone is evanished and turned into a Chimera If it be said how can such a Fluid Body as Water be able to support any part of the weight of the stone that is such a heavy Body I answer there is here no difficulty for if the imaginary surface K L upon which the 10 pound of the stone rests be able to sustain 10 pound of Water I suppose the stone taken away and the place of it filled with Water then surely it must also be able to sustain 10 pound of the heaviest metal seing ten pound of Lead or Gold or Stone is no heavier than 10 pound of VVater If some say this rather seems to be the reason why the Water becomes heavier after the stone is drowned because it possesseth the place of as much Water as would weigh 10 pound not as was said because the VVater supports 10 pound of it Therefore it may be judged and thought that if the space that the stone occupies were filled with Air or some light Body without sensible weight the VVater would become heavier than before
For example if instead of the stone there were placed a bladder full of wind within the VVater and tied to the bottom with a string that the surface might swell from H I to A B the VVater of the Vessel would become as much heavier than before as is the bulk of VVater equal to the quantity of the bladder Therefore the VVater becomes heavier not because it supports any part of the stone but because the stone occupies as much room and space as would contain 10 pound of VVater for by this means the drowned stone raiseth the VVater from H I to A B and so the Cylinders A C and B D being higher press with greater weight upon the bottom C D even with as much more weight as if the space that the stone occupies were filled with VVater For answer to this we shall make this following Experiment Take the Vessel M P V X and fill it with VVater to Q R. Next take a large bladder W Y full of wind and tying the neck with a threed thrust it below the Water and fasten it to the bottom with a string to the Ring Z. This done the Water swells and rises from Q R to M P. Now if it be true that the Water in the Vessel becomes heavier not because it supports 10 pound weight of the stone but because the stone occupies the room of 10 pound of Water then it ought to follow that after the bladder is tyed below the Water the said Water should become heavier than before even by three pound for I suppose a bulk of Water equal to the bulk of the bladder to weigh as much And the reason is because as you say the quantity of the bladder W Y makes the water swell from Q R to M P by which means the Pillars of Water M V and P X becomes higher and so presseth with greater weight upon the bottom V X. For clearing this difficulty I say when a bladder is thus below the VVater tyed to the bottom the VVater becomes not three pound heavier for when you place the Vessel with the VVater and bladder in the Scale of a Ballance the said VVater weighs no more than if it wanted the bladder therefore the VVater becomes not heavier because the stone possesseth the room of 10 pound of Water but because the Water sustains 10 pound of the stone Now the reason why the bladder makes not the water heavier though it raise it from Q R to M P is this because though verily there be a greater Pressure then before even upon the bottom of the Vessel yet because moe parts are not added the natural weight cannot be augmented which essentially depends upon the addition of these parts If it be replyed the Experiment of the bladder is to no purpose because it being knit to the bottom pulls up the Vessel with as great force as the growth of the Pressure bears it down and so the Bladder cannot make the Water heavier But if so be it were possible that the Bladder could remaine within the middle of the Water without being knit to the bottom and consequently without pulling up the Vessel then surely the Pillars of Water M V and P X being higher would press with greater weight upon the bottom and so make the Vessel and the Water weigh more in the ballance for 't is to be supposed that during all this time this Vessel with the Water is in one scale and a great weight of stone or lead in the other So would the Water A B C D become heavier likewise provided the space and room that the stone fills among the Water remained intire after the stone is taken away because that room and empty space remaining would keep the surface as high as A B by which means the Pillars A C and B D being higher would press with greater weight upon the bottom and cause the Water weigh more in the ballance I answer though by some extraordinary power the bladder could remain below the water of its own accord as it were and though the space and room by that same power which is left by the stone were keeped empty yet shall they never be able to make the Water heavier As to the reason that 's brought I answer the rising and swelling of the Pillars will make indeed a greater Pressure upon the bottom of the Vessel but because this Pressure may be produced and generated without the addition of new parts therefore it can never make the Water heavier for if this were true then it would follow that the more a body is comprest it should be the heavier which is contrary to sense and experience This Pressure is like unto Bensil that cannot weigh in a ballance though the thing bended do weigh as a Bow that weighs so many pounds but the Bensil of it weighs nothing Next will any man think that a Cub of Water six foot high and six foot thick will weigh more in a ballance then it did after it is turned into a long square Pillar 216 inches high I grant there is near 60 times a greater Pressure upon the bottom of the Vessel yet because this Pressure is generated without the addition of new parts it cannot make the Water heavier Moreover it is mechanically possible to keep the VVater S T V X under that same degree of Pressure it hath though the rest above were taken away if this be then it ought to be as heavy as the whole seing it still Presses the bottom with that same degree of Pressure it had from the whole but what is more absurd than to say one part of VVater is as heavy as the whole e. g. a pint as heavy as a gallon If it be said the Pressure and the weight are but one thing at least effectively which is sufficient to the purpose in hand as is clear from the Theorem 23. I answer they are but one thing indeed in order to the Ballance of Nature but they are neither formally nor effectively the same thing in order to the Libra or Artificial Ballance whereof we are now treating I shall conclude with this while the Vessel with the VVater is thus placed in the Scale of the Ballance and in equilibrio with the opposite Scale cut the string that tyes the bladder to the bottom and when it comes above you will find the VVater just of the same weight it was of for though the surface M P by taking out the bladder settle down to Q R yet there 's no alteration made in the weight From this I gather that if the swelling of the VVater should make it heavier then the subsiding and falling down of it ought to make it lighter From these Experiments we gather first that in VVater there is a Pressure because it sustains 10 pound of the stone F G. Secondly that whatever heavy body is weighed in Water it loseth just as much of its weight as the bulk of Water weighs it puts out of its place This is evident because the stone is 10 pound lighter in VVater than in the Air because the VVater that would fill the room of the stone is just of that weight VVe
see thirdly that the Pressure of VVater and the natural weight of it are two things really distinct because the Pressure may be augmented without any increment of the natural weight VVe see fourthly that the Pressure or Bensil of a Fluid cannot affect the Scale of a Ballance but only the natural weight VVe see fifthly that a body naturally heavier than Water weighs in Water because the stone F G makes the Water about it 10 pound heavier If it be inquired whether bodies that are naturally lighter will weigh in Water I answer if they be of any sensible weight they weigh as well as the other For this cause I except Air. For though they were never so light in respect of Water yet if they have any considerable gravity with them they will make the Water heavier they are among Put the case the Body were a Cube of Timber of six inches weighing sixteen ounces and that a Cube of Water of that quantity weighed 112 ounces Here 's a great inequality between their natural weights yet if that piece of Timber were made to exist in the middle of Water as the Bladder doth it would make it 16 ounces heavier The reason is this these 16 ounces are either supported by a surface of Water or they support themselves This last is impossible If the VVater support them then must they make the said VVater 16 ounces heavier Note that though a Body naturally lighter then VVater as Cork may be said to weigh in Water that 's to say to make it heavier in which sense VVater weighs in Water because if you add a pint to a gallon it makes it heavier yet if you take a piece of Cork and knit it to the Scale of a Ballance by a threed the Cork hanging among the VVater the Scale hanging above in the Air it will not weigh in Water because in this sense no Body weighs in Water but that which is naturally heavier then VVater as Lead or Stone In this sense VVater doth not weigh in Water as will be seen in the 17 Experiment EXPERIMENT IX Figure 13. Take a Glass-pipe 70 inches long or there-about and of any wideness having the upper end H hermetically sealed the lower end C compleatly open and fill it with Mercury and cause a Diver carry it down to the ground of the sea M N where I suppose is standing the Vessel A B D E with stagnant Mercury and drown the end below the surface A B. This being done the Mercury falls from the upper end H to the point G and there halts the space H G being empty For understanding this Experiment I shall propose several questions and answere them First what 's the reason why the Mercury subsides and sinks down from H to G I answer as formerly in the like cases inequality of weight between the Pondus of the impending Quick-silver and the Potentia of the surface of the stagnant Quick-silver D C E. For while the Tub is compleatly full the weight is so great that the surface D C E is not able to sustain it therefore it must fall down seing motion necessarily followes in Fluids upon inequality of weight It may be inquired secondly why it halts at G 58 inches from A B and comes no further down I answer it halts at G because when it hath fallen down to that point there happens equality of weight between the suspended Pillar and the foresaid surface for whatever weight the said Pillar is of the surface on which it rests is of the same In a word the Pondus of the one and the Potentia of the other are now equal For understanding this consider according to the 25 Theorem that the weight of the Element of Air upon the surfaces of waters is equivalent to the burden of 34 foot of water therefore the first and visible surface of this Water L I K is really as much prest with the burden of the Atmosphere as if it had 34 foot of Water upon it Consider next that between the said surface and the ground M N are 34 foot of Water indeed Consider thirdly that a Pillar of Water 34 foot high is exactly of the same weight with a Pillar of Mercury 29 inches high for if Water be 14 times lighter than Mercury then they cannot be of equal weight unless the one be 14 times higher than the other Now supposing the weight of the Air upon the surface L I K to be equivalent to 34 foot of Water or which is the same thing to 29 inches of Mercury the surface of the stagnant Mercury A B must be as much burdened with the incumbing Water and the Air together as if it had really resting upon it a Pillar of Mercury 58 inches high If this be then it follows by necessity that there must be an equality of weight between the pondus of the Mercury in the Tub and the potentia of the surface D C E Or which is all one thing that the part C on which the Pillar rests is no more burdened than the part D or E. For if 34 foot of Water and 34 foot of VVater be equivalent for weight to 58 inches of Mercury then must the part D and E be as much burdened with the said weight as the part C is burdened with the Pillar within the Tub seing both are of the same height therefore the power and force of the imaginary surface of the stagnant Mercury D C E is of the same strength with the weight of the Pillar G F B. And this lets us see the reason why the whole 70 inches cannot be suspended for if the outward Pressure that 's upon A B be but equivalent to the Pressure of 58 it can never make the surface D C E able to support 70. To make it evident if any doubt that the Mercury is suspended by the weight of the Water and the weight of the Air superadded let a Diver bring up this Engine to the top of the Water and he will find the one half to have fallen down namely from G to F the other half F B remaining And if it were possible to convey this Experiment to the top of the Air the Bearer would see the remaining half to fall down likewise and become level with A B for where no Pressure of Air is there can be no Mercury suspended This falling down is not all at once but by degrees and keeps a proportion with the Pressure of the Air that grows less and less from the ground to the top From this Experiment we see first the great Pressure and weight the Elements of Air and Water are under seing this Water that 's but 34 foot deep sustains the Mercury between G and F 29 inches as much between F and E being kept up by the Pressure of the Air.
C G D must be far heavier than the 58 inches of Mercury H B. The reason is clear because the said Pillar is not only 34 foot high but as thick as the Diameter of the Tub whose sides are three inches thick I answer the whole weight of that Water E A F C G D is not found while a man poises the Tub between his fingers but only the weight of the part G A which is exactly the weight of the Mercury H B. But here occurrs the great question namely why I find only the weight of the Water G A and nothing of the weight of the Water C E or D F I answer I cannot find the Pressure of the Water C E because it is counterpoised with the upward Pressure of the Water I K. And for the same reason I cannot find the weight of the Water D F because it is counterpoised by L M but because there is nothing between H and A to counterpoise the downward Pressure of the Water G A therefore I find that If it be objected that the Water I K cannot counterpoise the Water C E because the one is farder down than the other and consequently under a greater Pressure than the other I answer though I K be stronger than C E yet a compensation is made by the weight of the Tub. For understanding this let us suppose the Water C E and D F to press downward with the weight of six pound and the Water K I and L M to press upward with the weight of ten pound there being four pound in difference Suppose next the Tub to weigh in the Air ten pound and in the Water only six pound If this be then according to the eighth Experiment and eighteenth Theorem four pound weight of the Tub must rest upon the surface I L. And if this be then must the Water I K and L M be four pound weaker with the Tub than without it and must only have six pound of upward Pressure From these Experiments we conclude first the truth of the tenth Theorem namely that the weight of a Fluid is only found by sense when the Pressure is not uniform and equal This is evident from our finding the weight of the Pillar of Water I H as in the 13 Figure We conclude secondly that in all Fluids there is a pondus and a potentia as is clear from the pondus of Water E A F C G D that presseth down the Tub and the potentia of the Water I K L M that presseth up the same Tub. We see thirdly that there cannot be two surfaces of Water differing in altitude but they must differ in degrees of Pressure because the surface E A F is weaker than the surface I L that being higher than this We see fourthly that two surfaces differing in strength may be made equal by some Body or other interveening because though I L be stronger than E A F yet seing it supports four pound of the Tub it presseth up with no more force than E A F presseth down with We see fifthly that a Body suspended in a Fluid as in Air or in VVater may have one part of it prest equally with that Fluid and another part unequally this is evident because the parts E and F are equally prest with the Pillars C E and D F seing this Pressure is counterpoised with the Pressure of VVater I K and L M. But the middle part of the Tub A is unequally prest seing it is prest downward with the VVater G A but not prest upward with the Mercury B H. VVe see sixthly that whatever be the thickness of a Pillar of a Fluid yet no more of its weight is found or is sensible than the part which presseth unequally for though E A F C G D be a Pillar six or seven inches thick yet no more of the Pressure is sensible than what comes from G A. VVe see seventhly that a Body equally prest with a Fluid weighs less but a Body unequally prest weighs none at all This is clear in many particulars for a Stone weighed in VVater loseth not all the weight but a paâ—t because it is equally pressed But a Body unequally prest as is the Mercury H B hath no weight at all as it now stands For understanding this you must consider that the whole weight of it tests upon the surface of VVater I L. Therefore though it could be weighed by a string passing from the top H to a Ballance existing in the Air yet the said Ballance would find none of its weight seing it is wholly suspended by the VVater but a Stone so weighed is only suspended in part by the Water EXPERIMENT XI Figure 15. A M Z C is a Water 15 foot deep A B a Glass-tub 14 inches long and full of Mercury B C a Pillar of Water 13 foot 10 inches high thorow whose middle goes a string to the scale of the Ballance K existing in the Air. D E is a Tub full of Mercury 28 inches long with a Pillar of Water above it E F 12 foot and eight inches G H a Tub 42 inches long with a Pillar of Water above it H I 11 foot and six inches high And lastly A D G S M an imaginary surface 15 foot deep This Experiment is brought hither to demonstrate that a heavy Body weighs as much in Water as in Air which is point-blank to the common received opinion and destructive of the 18 Theorem To evince this I must suppose the 14 inches of Mercury in the Tub A B to weigh 14 ounce and the 28 inches of Mercury D E to weigh 28 ounce the 42 inches G H to weigh I mean in the Air 42 ounce Now I say to make a just equipondium between the two Scales K and L there must be 14 ounce put into the Scale L. If after this manner you weigh the Tub and Mercury D E 28 ounces will be required in the Scale L and 42 if you weigh the Tub and Mercury G H. For proving this Doctrine I must appeal to Experience which will not fail in this If you reply and say upon supposition the Tub and Mercury G H were a solid piece of brass or iron thus suspended in the Water ought it not to weigh less here than in the Air even as much less as is the weight of the quantity of Water it puts out of its place why then should not the Pipe H G with the Mercury in it do the same seing there is no apparent difference between them as to this But to leave this which will appear afterwards and to let the Reader see the truth of the 18 Theorem I affirm 't is not the weight of the 14 ounces of Mercury A B that burdens the scale of the Ballance K and that makes a counterpoise with the 14 ounces of Stone or Lead that 's in the scale L. What then is it you say I answer 't is 14 ounces of the Pillar of Water B C that does
this Neither doth the weight of the 28 ounces of Mercury D E burden the Ballance but only 28 ounces of the Water E F. Neither doth the Ballance support the weight of the 42 ounces of Mercury G H but it is only burdened with 42 ounces of the Water H I. The reason is most evident because according to the Principles of the Hydrostaticks already laid down the Cylinder of Mercury A B within the Tub A B rests immediatly upon the imaginary surface of the Water A D G and therefore cannot burden the scale in any wise The same is true of the other two Cylinders of Mercury But in this I find small difficulty The greater is how to make it out that the scale K supports 14 ounces of the Water B C and 28 of the Water E F and 42 of the Water H I. To make this seem probable consider first as was noted that this VVater is 15 foot deep and consequently the Pillar of VVater B C 13 foot 10 inches The VVater E F 12 foot eight inches And H I 11 foot and a half Consider secondly though this be true yet we must count the Pillar of VVater Z M 49 foot high The reason is evident because the Pressure of the Air upon the surface of all Waters according to the 25 Theorem is equivalent to 34 foot of Water this then being added to 15 makes 49 and by this reckoning the Water B C is 47 foot ten inches the Water E F 46 foot eight inches And lastly the Water H I 45 foot six inches Thirdly for easie counting I must suppose the whole Cylinder Z M to weigh 42 ounces every 14 inches one ounce and consequently the Water B C to weigh 41 ounces the Water E F to weigh 40 ounces the Water H I 39 ounces Note that in Physical demonstrations 't is not needful to use Mathematical strictness in counting and so leaving out fractions we shall onely use round numbers Consider fourthly that in all Fluids as hath been frequently marked there is a pondus and potentia the Water B C being the pondus and the Mercury A B the potentia the one striving to press down the Tub the other striving to press it up Consider fifthly that by how much the more a Body suspended in a Fluid is pressed up by so much the less the weight that presseth it down is foâ—nd and contrariwise by how much the less it is pressed up by so much the more the Pressure above is found Consider sixthly the less that a surface of Water is burdened the more able it is to counterballance the opposite Pressure and the more it is burdened it is the less able Consider seventhly that the Mercury A B which is evident in all Fluids not only presseth downward and burdens the surface A D G but also presseth upward and therefore actually endeavours to thâ—ust up the Tub and so it is that the Tub is pressed between two namely between the Water C B and the Mercury within it Now from these considerations I say the scale K must support and bear up 14 ounce of the Water B C for seing the Mercury is supported by the surface of VVater on which it rests it cannot by any means burden the ballance with its weight and seing it actually presseth up the Tub according to the seventh consideration it must so much the more counterpoise according to the sixth the opposite Pressure of the VVater B C and consequently diminish the weight of it so that the Ballance cannot support the whole but a part For according to what degrees of force the Mercury presseth up the Tub with according to the same must the Pressure upon the top of the Tub be diminished and so if the Mercury press up the Tub with the force of 27 ounce the VVater B C must press it down with 14 ounce only and so the Cylinder B C that weighs really 41 ounce must press the top of this Tub only with 14 which 14 ounce really counterpoiseth the 14 ounce of Stone in the Scale L. But how is it made out that the Mercury A B presseth up with 27 ounce For understanding this remember that the VVater is 49 foot high taking in the Pressure of the Air and that a VVater of that deepness is able to support 41 inches of Mercury every inch weighing one ounce For if 14 of Water be able to support one of Mercury 49 foot or 567 inches must support 41. If then the part of the surface A be able to weigh 41 it must have of upward Pressure 27 ounces seing it's counterpoised de facto only with 14. Take notice that in the Hydrostaticks the word pressing or weighing as really and truly signifies a weighing up as a weighing down seing it is no less essential to Fluid Bodies to move upward than downward and that with equal force and weight According to this reasoning the Ballance supports 28 ounces of the Water E F Imagine the second Tub to be suspended as the first seing the Cylinder of Mercury D E presseth up the Tub only with the weight of 12 ounce which 28 ounce really counterpoiseth the 28 ounce of Stone in the Scale L. But why doth the Mercury A B press up with 27 ounce and the Mercury D E with 12 For answer remember according to the sixth consideration the shorter a Cylinder of Mercury is the surface upon which it rests is the stronger and more able to press it up and contrariwise the longer it is the surface is the more unable and weak therefore A B being shorter and lighter than D E the surface of Water must press it up with greater force so that if the said surface A M be able to press up the Mercury A B with 27 ounce it must press up the Mercury D E only with 12 ounce According to this rule if the Mercury A B were 15 inches high it would press up only with 26 ounce if it were 16 with 25 if 17 with 24 if 18 with 23 and so forward This leads us to a clear discovery of all the secrets here for if the Mercury A B thrust up the Pipe with the weight of 27 ounce then must the Scale K be eased of so much weight and so much must be subtracted from L. Now let us imagine the Pipe A B to be empty both of Air Water and Mercury in this case 41 ounce must be in the Scale L to counterpoise it seing the whole Cylinder B C that weighs so much does now really counterpoise it Let us imagine next these 14 inches of Mercury to rise and fill the Tub A B in this case there happens a great alteration because the rising of them are really equivalent to the subtracting of 27 ounce from the Scale L and the reason is because by so rising and filling the Tub they thrust up the said Tub and by this means easeth the Scale K of so much weight Now this Scale being eased you must of necessity
take out from L 27 ounce for making a new counterpoise And lastly the Scale K must support the whole weight of the Water H I which is 39 ounce nothing remaining to counterballance this downward Pressure and consequently to ease the Ballance How then is it counterpoised For clearing this you must remember that this Water that 's really 15 foot deep must be reckoned as I said 49 because of the Pressure of the Air upon the top that 's equivalent to 34. If then it be so it cannot raise Mercury higher in a Tub than 42 inches the one being 14 times heavier than the other so that if 14 inches of Water cannot raise Mercury higher than one inch 49 foot cannot raise it higher than 42 inches for as 14 inches are to one inch so is 49 foot to three foot and an half which is 42 inches Now I say the whole weight of the Water H I rests upon the top of the Tub and so presseth down the Scale K to which you must imagine this Tub knit by a string as the former was nothing remaining to counterpoise this downward Pressure for the top of the Mercurial Cylinder being raised as high within the Pipe as the surface of Water D G S is able to raise it the said top can impress no force upon the Tub within to thrust it up and so to ease the Scale K. For example when a man erects upon his hand a Cylinder of Timber or any such like thing which is the outmost he can support he will not be able to impress any impulse upon the seiling of a room above his head but if so be in stead of that taken away there be one lighter erected which he is able to command he can easily thrust up the seiling at his pleasure Just so it is here for the 42 inches of Mercury being the outmost that the surface of Water D G S is able to bear it cannot impress any impulse therewith upon the top of the Tub within but easily can the Cylinder D E impress an impulse and more easily the Cylinder A B seing they are lighter and so more powerful To evidence this a little more let us imagine two things first the Tub G H to be empty as if vacuity were in it In this case the top of the Tub ought to bear the whole burden of the Water and consequently the Ballance to bear it also because there is not a potentia within the Tub to counterpoise this pondus Next let us imagine the Tub to be only full of Water according to this supposition the Ballance cannot be in the least part burdened because the Water within the Pipe presseth it up with as much force as the Water I H presseth it down and if any thing should burden the Ballance it would be only the weight of the Pipe that 's not considerable From what is demonstrated we see first that though this Experiment would seem to prove at the first that a heavy Body weighs as much in the Water as it doth in the Air because the whole weight of the Mercury A B is found in the scale L yet 't is not so because the 14 ounce of Stone L doth not counterpoise any of the Mercury A B but 14 ounce of the Pillar of Water B C. Secondly there 's here a clear ground for asserting a pondus and a potentia in Fluids because this Tub A B is prest down with the VVater B C and prest up with the Mercury within it Thirdly there 's here a clear ground for asserting the Pressure of VVater even in its own place because the Water B C counterpoises by it's weight the 14 ounce of Stone L. Fourthly we see an excellent way for finding the weight of any Cylinder of Water for whatever be the weight of the Mercury in the Tub the Cylinder of Water that rests upon the top will be of the same weight exactly this is evident in comparing the weight of the Mercury G H with the weight of the Water H I. Fifthly that whatever be the height and weight of a Pillar of Water yet the Ballance can sustain no more of it than the just weight of the Mercury this is also evident because the scale of the Ballance supports no more of the weight of the Water B C than the just weight of the Mercury A B. We see sixthly the further down a Pipe with Mercury goes through Water the greater is the Pressure it makes upon the top of the Tub within for put the case this were 100 foot deep the Mercury G H that wants all upward Pressure now would press up the Tub with 40 ounce the Mercury D E with 55 and the Mercury A B with 70. We see seventhly the shorter a Cylinder of Mercury be it is the stronger in pressing and longer it be it is the weaker for there 's more strength in A B than in D E. We see eighthly that the strength decayes and grows according to Arithmetical progression as 1 2 3 4 because if you make the Cylinder G H 41 that 's now 42 it presseth up with one ounce Make it 40 inches it will press up with two ounces of weight Make it 39 it presseth up with three And contrariwise make the Cylinder D E 29 inches that 's now but 28 it will press up with 11 ounce only VVith 28 it presseth up with 12. Make it 30 inches high it will press up with 10. If it be 31 inches it presseth up with nine and so forward Lastly make the Cylinder A B 15 inches that 's now but 14 it presseth up with 26 with 14 it presseth up with 27 make it 16 it presseth up with 25 make it 17 it presseth up with 24. We see ninthly that in Fluids we may make a distinction between a sustentation and an equipondium 'T is evident here because there 's a perfect equipondium between the 42 inches of Mercury G H and the outward Water that 's 49 foot deep But 't is not so between the said Water and the Mercury D E because the said Water is able to raise the said Mercury 14 inches higher therefore the Water only sustains the Mercury D E but counterballances the Mercury G H. We see tenthly that the pondus of the pillar of Water B C is counterpoised by two distinct powers really The one is the 14 ounce of Stone in the scale L the other is the 14 inches of Mercury A B that as really thrusts up the Water as the scale K pulls it up by vertue of the opposite weight Eleventhly take away the Stone L and you will find the Pipe with the Mercury A B sink down this happens not because the surface of Water on which it rests is not able to sustain it but because the 14 ounce of the Water B C that was supported by the Stone doth now press it down Twelfthly the more a Body is unequally pressed by a Fluid the more of the weight of that Fluid is
sensible and the more equally a Body is pressed the less sensible is the weight of that Fluid this is evident because there 's a greater weight of the VVater H I found in the Ballance it takes 42 ounce to counterpoise it than of the VVater E F which is counterpoised with 28 ounce and the reason is because the top of the Tub H supports the whole 39 ounce of VVater H I the Mercury within the Tub not being able in the least to counterpoise it or thrust it up But because the Tub D E is more equally pressed the VVater E F presseth down with 40 and the Mercury D E presseth up with 12 therefore less weight of the VVater E F burdens the Ballance only 28 ounce Hence it is that because the Tub A B is more equally pressed than either D E or G H there 's less of the weight of the VVater B C found in the Ballance only 14 ounce Thirteenthly if in the instant of time while the Tubs are thus suspended in the VVater the Pressure of the Air above were taken away and annihilated then first the 42 inches of Mercury G H would fall down to about 13 inches Secondly the 28 inches of Mercury D E would fall down to as many And lastly the 14 A B would sink down to the same height The reason is because the Pressure of the Air being equivalent to 34 foot of VVater no more would remain but 15 foot which is the real height according to Z M. But 15 foot of Water cannot sustain moe inches of Mercury than about 13. And consequently first 14 ounce of Stone in the Ballance would counterpoise the whole Water B C. The reason is because the Water B C is but of 14 ounce and the Mercury A B being but 13 inches high could impress no impulse upon the top of the Tub within that 's 14 inches high Secondly 13 ounce of Stone in the Scale L would counterpoise the whole Water E F seing E F is but 13 ounce Thirdly the same weight one ounce being deduced would counterpoise the Water H I because in this case it weighs but 12 ounce To proceed a little further imagine the Pipe G H to be suspended by the ballance as the Pipe A B is and then a little hole opened in the top H to suffer the Water to come in till the Mercury subside 14 inches namely from Q to O imagine this Tub to be the other and then stop it The reason why the VVater rusheth in and presseth down the Mercury is the force and Pressure of it for the said VVater finding the Cylinder in equilibrio with the outward VVater presently by its own weight casts the scales which is easily done seeing the surface G S M supports as much burden as it can But that which is more considerable is this after the subsiding of the Mercury from Q to O the equilibrium that was between the scale of the ballance and the VVater Q R is destroyed for whereas 42 ounces were required before 29 will now do it For understanding the reason of this consider that between Q and O are 14 inches of VVater rushed in which are equivalent to one inch of Mercury Next according to former reasonings the ballance must support 29 ounces of the VVater Q R because in this case the top of the Pipe within is pressed up with the weight of 13 ounces which in effect diminisheth as much of the downward Pressure of the VVater R Q which before had the burden of 39 ounces But why is the Tub prest up with 13 ounces I answer because the Mercury that before was 42 inches is now but 28 or having the 14 inches of Water Q O above it it is 29 therefore being shorter the surface G S M is the more able to Press it up even with as much more force as it is in inches shorter In the second place let in as much Water more as will depress the Mercury other 14 inches namely from O to P. In this case 16 ounce of stone will make an equipondium because the 14 inches of Mercury P S and the 28 inches of Water P O Q being a far lighter burden by 26 than the 42 inches of Mercury the surface G S M must be far abler to press them up now than before and therefore must diminish as much of the downward Pressure of the VVater Q R that burdens the Ballance as themselves wants of weight seing then the whole Cylinder of Mercury and Water together are but equivalent for weight to 16 inches of Mercury the top of the Tub within must be prest up with 26 ounce and therefore they by their upward Pressure must diminish 26 ounce of the weight of the Water R Q that weighs 39. Lastly let in so much VVater as will depress the last 14 inches P S and you will find no more weight required in the Ballance to make an equipondium than counterpoiseth the simple weight of the Tub which is not considerable The reason is because the part S of the surface G S M being liberated of the burden of Mercury and sustaining only the VVater within the Tub in stead of it this surface presseth up the VVater within the Tub and consequently the top of it with as great force and weight as the top of the Tub without is depressed with the outward VVater R Q therefore 39 ounce depressing the Tub and 39 ounce pressing it up the Ballance must be freed of the whole weight of VVater R Q. If it be objected that the 42 inches of VVater Q S are equivalent in weight to three inches of Mercury therefore the part of the surface S being burdened with this cannot press up with as great force as the VVater R Q presseth down For answer consider that the part S is able to support 42 ounce of VVater and next that the VVater R Q weighs but 39. Then I say seing the 42 inches of VVater within the Tub weighs only three ounce the part S that 's burdened therewith being able to support 42 it must press up with the weight of 39 and so counterballance the VVater R Q. If it be inâ—uired whether or not would the 14 inches of Mercury A B fall down a small hole being made in the top of the Tub at B I answer they would If it be objected that these 14 inches of Mercury are not in equilibriâ— with the Pressure of the ambient Water as the Mercury G H and therefore they cannot be so easily depressed by the Water that comes in at the said hole I answer they must all fall down and as easily as the other and that because of inequality of weight between the Potentia of the surface of VVater and the Pondus It 's certain the part A of the surface cannot support more weight of any kind than 42 ounce but when a hole is opened in B and the VVater coâ—es in 't is then burdened with the weight of 14 ounce of
Mercury and with the weight of 41 ounce of VVater so much the VVater B C weighs which is 55 ounce but a surface that hath only the Potentia of 42 can never support a Pondus of 55 no not of 43. It may be objected thus Put the case a Cylinder of Gold or Brass were suspended in this VVater as the Pipe and Mercury G H are suspended by the Ballance would not the Ballance support the whole weight of it without supporting any part of the weight of the VVater I H that rests upon the top of it I answer there 's a great difference between the two because a Cylinder of Gold or Brass suffers both the upward and downward Pressure of the VVater but the Mercury G H suffers only the upward Pressure being freed of the downward by the top of the Tub. From this Experiment of letting in the VVater upon the top of the Mercury we see first that when two Fluids are in equilibrio one with another a very small weight will cast and turn the Scales because if the sixth part of an inch of VVater come in at Q it presently alters the hight of the Mercury from 42 inches to less Secondly 't is impossible for a surface of Water to support more weight than its own proper burden because the part S cannot support more no not a grain than 42 ounce VVe see thirdly that it is as impossible for a surface of VVater to support less than its own burden because whatever loss of weight the Pillar of Mercury S Q suffers by the ingress of the VVater Q O it s made up again by the same VVater If it be objected that the 14 inches of VVater Q O are not so heavy by far as the 14 inches of Mercury that fell down I answer its true yet the part S is as much burdened as before because what is wanting in weight it s made up and compensed by Pressure VVe see fourthly that the Pressure of a Fluid is a thing really distinct from the natural weight according to the 22 Theorem because though the 14 inches of Water Q O are not so heavy naturally as the 14 inches of Mercury that fell down yet the Pressure of them upon the surface S is as much We see fifthly that 14 inches of Water that 's â— body fourteen times lighter than Mercury may have as much weight with them as 14 ounce of Mercury We see sixthly that a Cylinder of Mercury cannot be suspended in Air or in Water unless it be guarded with a Tub to preserve it from the downward Pressure of that Air or Water for by opening an hole in Q the Meâ—cury subsides We see seventhly that 't is impossible 〈…〉 Fluids to suspend one another mutually unless there be a sort of equipondium between them because no sooner you destroy the equipondium between the 42 inches of Mercury Q S and the part of the surface S by the ingress of the Water Q O but assoon there ariseth a new one We see eighthly as we noted before the nearer a Body comes to be equally pressed with a Fluid the less is the Pressure of that Fluid sensible because less weight is required in the Ballance to counterpoise the Pressure and weight of the Water R Q after the ingress of the Water Q O P than after the ingress of the Water Q O. We see ninthly that when a Body is equally and uniformly preâ—â—ed with a Fluid the Pressure is insensible because after the Water hath thrust down all the Mercury from Q to S there 's no more weight at all of the Water R Q found in the Ballance We see tenthly that not only in Water the Pressure of Water may be found but out of it namely in the Air as is clear from the Ballance that supports the Pressure of the Water R Q. We see eleventhly a ground to distinguish between the natural Ballance and the artificial Ballance The artificial Ballance is the Ballance K L the natural is the Pipe Q S. We see twelfthly that they keep a correspondence between themselves or some Analogy for by what proportion the Water thrusts down the Mercury by that same proportion the pondus L of the Ballance is lessened and by what proportion the Mercury rises in the Pipe by that same is the weight L augmented in the Scale We may subjoyn lastly that the easiest way of explicating the Phenomena of Nature is not always the best and truest For some may think it were far easier to say that the Ballance supports the Mercury A B or D E and not any part of the Water B C or E F. But such a way would be false and absurd and contrary to all the former Doctrine EXPERIMENT XII Figure 16. THis Schematism represents a Water 100 foot deep whose first and visible surface is I H K. And L M is the ground of it C D is a piece of brass 30 inches high and 12 inches in diameter suspended upon the imaginary surface of Water A N B which is distant from the top I H K 25 foot This Brass cannot go farder down when demitted from H because it 's keeped up by the Force and Pressure of the surface of Water A N B which I prove thus The part B sustains de facto a Pillar of Water K B 1400 pound weight therefore the part N is able to sustain as much I suppose here the said piece of Brass to weigh 1400 pound The Water K B is 1400 pound because its a Pillar 25 foot high and 12 inches thick for one cubical foot weighs 56 pound Trois The connexion of the argument is evident because it is as easie for a surface of Water to sustain a solid Body as to sustain a Fluid Body therefore if the part B support the Fluid Pillar K B the part N must be able to support likewise the solid Pillar C D which is of the same weight Iâ— it be objected that the part N sustains besides the Brass C D a Pillar of Water E F 22 foot high and a half which two will weigh 2260 pound I answer upon supposition that neither Water nor Air succeeded the space E F being void of both the Brass would be suspended with the force and power of the Water N. And though this cannot be made practicable yet the Theory of it may conduce much for explicating the secrets and mysteries of the Hydrostaticks But why ought the Brass to be suspended at 25 foot from the top I answer because the potentia of the surface A N B is equal to the pondus of the Brass To evidence this consider that Brass is a Body naturally heavier then Water I shall suppose ten times that 's to say one inch of Brass will counterpoise ten inches of Water If this inequality be then must this Pillar of Brass go so much farder down than the first surface I H K as the one is heavier in specie or naturally than the other therefore it
must sink 25 foot exactly seing a piece of Brass 30 inches high requires 400 inches of Water or 25 foot to counterpoise it for if one inch of Brass require ten inches of Water then surely 30 inches must require 300. Yet it is no matter what the thickness be provided it be no higher than 30 inches To advance some farder let us make a second supposition namely while the Brass is thus suspended upon the surface A N B suppose the Air to come down and fill up the imaginary space E F then must the Brass be thrust down as far as the surface O P that 's 34 foot below the surface A N D and 59 from the top The reason of it is this because the weight of the Air superadded is equivalent to the Pressure of a Pillar of Mercury 29 inches high and 12 inches thick therefore the Brass being burdened with this it must go so farder down till it meet with a surface whose potentia is equal in weight to the pondus of both which is precisely 59 foot from the top for if one inch of Mercury require 14 of Water then 29 inches must require 405 inches or 34 foot In a word it must go as far down as that surface that sustains a Pillar of Water that would counterpoise in a Ballance the Brass C D and a Pillar of Mercury 29 inches high and 12 inches thick both which weighs 3290 pound From what is said we see first that of two heavy bodies differing in weight the lighter may go further down than the heavier This is clear because a slender Cylinder of Gold in form of an Arrow half an inch thick and 28 inches long weighing 28 pound 't is no matter though the just weight of it be not determined will go down 35 foot in Water before it meet with a surface whose potentia is equal in weight to its own pondus for if Gold be 15 times heavier naturally than Water then the said Cylinder must go down before it rest 420 inches or 35 foot But a piece of Gold 12 inches long and six inches thick that perhaps will weigh 208 pound will sink no further than 15 foot And the reason is because if one inch of Gold require 15 of VVater to counterpoise it then 12 must only require 180 or 15 foot Note that both the bodies must go down Perpendicularly and not as it were Horizontally with their sides downmost for if they go down after this manner they cannot sink so far The reason of this is also evident because a heavy body goes so far down and no further till it hath thrust â—s much Water out of its place as will counterpoise it self in a Ballance That 's to say if an heavy body weigh 100 pound it must go no further down than after it hath thrust out 100 pound of Water But so it is that a piece of Gold in form of an Arrow going down side-wise or with the two ends parallel to the Horizon will thrust as much Water out of its place as will be the weight of it self before it can go down 15 or 16 inches from the top because for every inch it goes down side-wise it expellâ— 28 inches of Water In going down two inches it expells 56. In going down three inches it expells 84 and so forward till it go down 15 inches where it expells 420 inches but 420 inches amounts to 35 foot Now take a Cylinder of Water 35 foot high and just the thickness of the Cylinder of Gold which I supposed to be of half an inch and put them in a ballance and you will find the one just the weight of the other Neither can the piece of Gold go so far down as before if it go down side-wise because for every six inches it is drowned it expells a bulk of Water 12 inches long and six inches thick therefore it must be suspended before it go beyond 90 inches or seven foot and an half now if six inches give one foot 90 inches will give 15 foot but 15 of Water in hight and six inches thick is the just weight of it in a ballance viz. 208 pound We see secondly the broader and larger the surface of a Fluid be 't is the more able and strong to support an heavy burden therefore the part of a surface of Water six inches square every way will carry a far greater weight than a part four inches square Though a surface of Water 34 or 35 foot deep be not able to sustain a Cylinder of Gold if it exceed 28 or 29 inches in hight yet take a Cylinder of Gold 10 foot high and reduce it by making it thicker to the hight of 20 inches a surface of Water little more than 24 foot deep will sustain it Or reduce a Cylinder 10 foot high which requires a surface more than 100 foot deep to a Cylinder six inches high a surface little more than seven foot deep will support it We see thirdly the reason why bodies that are broad and large move â—lowlier through Air and VVater than bodies that are more thin and slender though both be of the same weight in a ballance For example 20 pound of Lead long and slender like an Arrow will go sooner to the ground of a deep VVater than a piece of Lead of the same weight in form of a Platter or Bason The reason is because as the body is broader so it takes a broader part of a surface which broader part is stronger and abler than a narrower part and so makes the greater resistance The same is the reason why a Bullet six inches in Diameter moves â—lowlier thorow the Air shot from a Cannon than a Bullet one inch in Diameter For the same reason Ships of seven or eight hundred Tun move far slowlier thorow the Air and Water than Vessels of less burden Item large and big Fowls as Eagles move slowlier than small Birds as Swallows Yea of Fowls of the same quantity one may move quicklier than another as is evident in long-wing'd Hawks as Falcons that by the sharpness of their Wings move far more space in half an hour than Kites or Gose-Hawks whose wings are rounder We see fourthly that there 's no body how heavy soever but it may be supported by the surface of a Fluid either in Air or in VVater I grant the strongest surface of Air that can be had is not able to support more weight than a Cylinder of Gold 28 inches high yet though it were as large and broad as a Mill-stone if it do not exceed the said hight the Air is able to sustain it For the same cause if it were possible to free a Mill-stone of the Air that rests upon it the Air below would lift it from the ground and carry it up many fathoms even till it came to a surface equal in power to the weight of the Stone Or if a large Mill-stone were demitted from the top of the Atmosphere towards the Earth it could hardly
six inches thick But this seems rather to flow from the disproportion of Magnitudes seing a circular plain 4 inches in diameter cannot receive a Base of a Pillar 6 inches in diameter But this is certain from the very nature of Fluids that in a deep VVater wherein may be distinguished 100 or 1000 different surfaces each one is able to support his own burden and no more EXPERIMENT XIII Figure 17 18 19. FOr making this Experiment take two plain Bodies of Brass or Marble well polished Make them of any quantity but for this present use let each of them be four inches broad square-wise Upon the back part let each one have an handle about six inches long of the same metal formed with the plain it self in the founding if they be of Brass as is represented in this Schematism When they are thus prepared anoint their inner-sides with Oyl or Water and having thrust the one face alongst upon the other with all the strength you have till all the four edges agree two whereof are represented by A B and C D you will find them cleave so closs together as if they were but one Body The effect is this that ordinary strength will not pull them asunder and that under a surface of Water a stronger pull is required than in the Air. That we may deduce some Hydrostatical conclusions from this Experiment let us suppose these two plain Bodies to be united in the middle of the VVater I K P Q that 's 34 foot deep and suspended by a beam or long tree T V existing in the Air near the top of the VVater by a chord S E passing between the middle of the beam and the end of the handle at E. Suppose next a great weight of Lead R 350 pound to be appended to the end of the handle at H of the under plain Body C D N O. This done I affirm that the beam T V neither sustains the under plain Body C D N O G H not the 350 pound weight of Lead R that hangs down from the handle G H. If it be objected that the beam supports the upper plain Body A B L M F E therefore it must bear the weight also of the under plain C D N O G H with the weight R seing they are both united together and cleave so closs as if they were but one Body I answer it supports the one unquestionably but not the other To explicate this Hydrostatical Mystery I must aver three things first that the inferior plain is supported by the upward Pressure 〈◊〉 the lower VVater P Q N O. Secondly that the burden which the beam sustains is not the weight of the under plain but the weight of the 34 foot of Water I K L M. Thirdly that this weight is exactly the weight of the inferior plain and Lead R. But is it not more easie to say that the beam supports both the plains I answer if I say so I can neither affirm truth nor speak consequentially But may it not be said that the inferior plain is supported both by the beam and the lower water P Q N O? I answer this is impossible because one and the same weight cannot be supported totally by two distinct supporters For making these assertions evident I must suppose the superior Water I K L M to be 34 foot deep and to weigh if it were put into a ballance 400 pound and which is unquestionable that the said Water rests upon the back of the superior plain L M. I suppose secondly that the lower Water P Q N O weighs as much and thrusts up the inferior plain with as great weight as the superior plain is prest down with by the superior Water This is evident from former Experiments And lastly I suppose each plain to weigh two pound and the weight of Lead R 350. It is to be observed here that no mistake may arise in the calculation afterwards that though it be said this 34 foot of Water weighs 400 pound yet in it self it weighs but 200 but considering the Pressure of the Air upon I K which is as much it may be truly said to weigh 400. These things being premitted I say the weight that the beam T V sustains is not the weight of the inferior plain and the Lead R but 352 pound of the superior VVater I K L M and consequently that the inferior plain is supported by the lower VVater P Q N O. The reason is because the lower VVater presseth up â—â—th the weight of 48 pound It is in it self 400 pound but being burdened with 352 it cannot thrust up with more weight than 48. Now it pressing up with 48 must ease the beam of 48 and counterpoise so much of the superior VVater and consequently the beam must support only 352 pound of it But put the case you say the weight R were 130 pound 160 pound or 180 pound would the beam be less or more burdened with the superior Water I answer if R be 130 pound then the beam supports only 132 pound of the superior Water for if the inferior be only burdened with 130 the weight of R and with two the weight of the inferior plain then must it press up with 368 and by this means must ease the beam of so much it sustaining 132 pound only According to this compting when the Lead R weighs 160 pound the beam supports only 238 pound of the superior Water If it weigh 180 pound it sustains 218. And if the weight R were taken away the beam supports no more of the superior VVater than two pound To proceed a little further imagine the two Plains to be drawn up 17 foot nearer the first surface I K namely as high as Z W. This done the union breaks up and they presently fall asunder The reason is because the surface Z W is not able to support 352 pound but only 300 which I prove thus If 68 foot sustain 400 then 51 foot must sustain 300. I say 68 and not 34 because as was noted the Pressure of the Air upon the surface I K is equivalent to other 34 foot and therefore though the deepness of this VVater between I K and L M be but 34 foot really yet it is 68 foot virtually and in effect Imagine secondly the surface I K to subside 17 foot namely to Z W. In this case the union is broken also and the lower Plain falls from the upper The reason of this is the same with the former because by what proportion you diminish the high of the superior VVater by that same proportion you diminish the upward Pressure of the lower VVater Therefore if you subtract from the superior VVater 17 foot that weighs 100 pound you subtract likewise 100 pound from the inferior VVater and consequently you make it press up only with 300 but 300 is not able to counterpoise 352. Let us suppose thirdly the superior Plain and the superior Water to be annihilated then I say the
Pressure and force of the under Water would thrust up the inferior Plain and the weight R about eight foot higher then X Y and there suspend them The reason is because the surface X Y being able to sustain 400 and being burdened only with 352 must have the weight of 48. Now the upper Plain being taken away and the upper Water also and the empty space of both remaining the said weight of 48 pound must carry the under Plain as high as is said Let us suppose fourthly the Pressure of the Element of Air that rests upon I K to be taken away then must the two Plain bodies be disunited the inferior falling from the superior The reason is because in this case the superior Water would have but the weight of 200 pound and consequently the inferior would press up only with as much but 200 is not able to counterpoise 352. From what is said we see first that in all Fluids there is an upward Pressure as well as a downward and that the one is alwayes of equal force to the other because the inferior Plain is pressed up with as great force as the superior Plain is pressed down with We see secondly that in Fluids there is a Pondus and a Potentia The Potentiâ— here is the inferior Water and the Pondus is the superior Or the 350 pound of Lead R may be called the Pondus which counterpoiseth the Potentia of the surface of VVater X Y. We see thirdly that though the Pressure of a Fluid be not the same thing with the natural weight yet it is equivalent to it because the 352 pound of Lead R is sustained by the Pressure of the inferior VVater which could not be unless they were virtually the same We see fourthly that there may be as much Pressure in one foot of Water as there is weight in 100 or in 1000 foot or in 1000 fathom For put the case these two plain bodies were suspended 100 fathom below the surface of the sea and within a foot or two of the ground as much weight would be required to pull them asunder as is the weight of a Pillar of Water 100 fathom high and 4 inches thick every way which will be more then 3000 pound weight besides the weight of the Air above that will weigh 200 pound This could not be unless there were as much Pressure in the lowest foot of this Water that 's 100 fathom deep as there is weight in the whole Pillar above We see fifthly the more the potentia of a surface is burdened the more sensible is the pondus because the heavier you make the Lead R that burdens the inferior Water the more weight of the superior Water rests upon the Beam We see sixthly the more unequally a body is pressed the more the Pressure is sensible For understanding this consider that the under-face of the superior Plain is more and less pressed according to the more and less weight the Lead R is of for put the case the inferior Plain were taken away the face of the superior Plain would be equally prest with the back of it But â—hen the inferior Plain is united to it the Pressure of the Water is kept off by which means the back is prest more than the face Now as the inferior Plain becomes heavier and heavier by making the weight R more and more weighty the less and less is the face of the superior Plain prest up Hence it is that as this inequality of Pressure becomes greater and greater so the weight of the superior Water affects the Beam more and more Or if the superior Plain were a sensible body as Animals are it would find the back of it more and more burdened according as the weight R becomes heavier and heavier We see seventhly that Water weighs in Water because all the weight the Beam supports is the burden of the superior VVater and not the burden of the inferior Plain or of the weight R. It supports the weight also of the superior Plain but this is not considerable This is only to be understood when the Pressure is unequal for if the upper Plain were as much prest up as it 's prest down the weight of the superior VVater would not be found by the Beam We see eighthly that the higher a surface be it is the weaker and the lower it be it is the stronger because when the two plain bodies are pulled up 17 foot they fall asunder We see ninthly the vanity of the common opinion that maintains two plain bodies to cleave closs together for fear of vacuity and that neither Humane not Angelick strength is able to break this union without the rupture and fracture of them both It may be enquired upon supposition that the inferior plain had four holes cut thorow the middle square-wise as A B C D in the 18 Figure what Phenomena would follow Before I answer consider that this Figure represents the inner face of the Brass-plate C D N O of the 17 Figure which as was supposed is four inches from 〈◊〉 to side and consequently contains 16 square inches Now imagine the under plain C D N O while it is united to the uppermost to have four square inches cutted out of it as A B C D. These things being rightly conceived and understood I say when the said holes are cutted thorow the beam T V that now sustains 350 pound shall by this means only sustain 250 pound To make this evident consider that the under plain as was said contains 16 square inches Next that the top of the inferior Water upon which the plain rests contains as many and that every inch of the Water weighs 25 pound seing the whole as was supposed before weighs 400 pound Now I say the beam must support only 250 pound of the Water I K L M because these holes being made the top of the inferior Water comes through them and presseth up the face of the superior plain with 100 pound and so easeth the beam of so much I affirm next that though the inferior Water N O P Q be in it self 400 pound and consequently able to support the inferior plain with the weight R albeit they weighed so much yet the said holes being cut out it is not able to support more burden than 300. The reason is because of 16 parts that did actually bear up before there are only 12 now that sustains And every one of these twelve being but able to support 25 pound it necessarily follows that the greatest weight they are able to sustain is 300 pound I affirm thirdly that if a fifth hole were cut through the under plain would fall from the upper because in this case the inferior Water is not able to support 350 pound as before seing of 16 parts there are five wanting and eleven remaining cannot support more weight than 275 pound Moe questions of this kind might â—e proposed as first what would come to pass if the the upper
other I answer this only proves that two Pillars differing in weight in the Libra or Artificial Ballance may be of one weight in the Natural Ballance because in the Artificial Ballance bodies counterpoise one another according to all their dimensions but in the Natural Ballance such as this Engine is Fluids counterpoise one another according to their altitude only From the first trial we conclude first that Water even in its own place gravitats and weighs because this Water by its Pressure de facto thrusts up 6 inches of Mercury We see in the next place that the Pressure of a Fluid is as easily communicated Horizontally as Perpendicularly because the Pressure runs alongst from H to B. We see thirdly that Fluids may have as much Pressure begotten in them even while they are environed about closely with solid bodies whereby the superior Pressure immediatly and directly by perpendicular lines is keeped off as if they were immediatly under the Pressure because the Mercury A B C D is as much burdened with the Pressure that comes from H as if the upper part of the Vessel A B were open to let in the superior Pressure by perpendicular lines The Air then under the roof of a house is under as great a Bensil and Pressure as the Air without that 's directly under the Pressure of the Atmosphere VVe see fourthly that the Pressure of a Fluid may be as easily communicated thorow the parts of Heterogeneous Fluids as thorow the parts of Homogeneous because the Pressure of the VVater K I is as easily communicated thorow the Air P H thorow the Water H B and thorow the stagnant Mercury B D to the orifice E as if nothing interveened but VVater VVe see fifthly that Mercury can suffer a Pressure as well as VVater or Air because the six inches cannot rise from B to G unless the stagnant Mercury A B C D were compressed even in all the parts of it From the second trial we see that there cannot be a Pondus in a Fluid unless there be a Potentia to counterpoise it for when you take away the Water R I by lifting up the Engine to the top of the Water the Mercury B G presently falls down From the third trial we conclude that the Pressure of a Fluid cannot be communicated thorow solid Bodies for when the Engine is drowned below the Water with the orifice I stopped no ascent of Mercury follows We conclude from the fourth trial that it is impossible for two Fluids to counterpoise one another unless they be in Equilibrio because the Water K I cannot sustain the Mercury B G unless it be of the same weight From the fifth we conclude that a Fluid may be keeped under the same degree of compression after the superior weight that begat it is taken away for after the Engine is brought above the Water with the orifice I stopped the Mercury B G is still suspended even by vertue of the Pressure that 's in the stagnant Mercury This tells us that a sphere of glass full of Air may retain its Bensil even though the whole Element of Air that begat it were destroyed From the sixth we gather that a Fluid cannot abide under Pressure when the burden is taken away that begat it or that keeped it under Pressure for by opening the orifice I the Air P H extends it self and so are the VVater and Mercury within the Vessel freed of their Pressure likewise We gather from the seventh trial that in the Ballance of Nature one Scale cannot be more burdened then another or that two Fluids cannot counterpoise one another unless they be in equilibrio for when you pour in 14 inches of Water upon the top of the Mercury at G they thrust down one inch that there may be a just equipondium between them and the opposite weight K I. We gather from the eighth trial which was observed before first that there cannot be a Potentia in a Fluid unless there be a Pondus to counterpoise it for when you suck out the Air G O which was the Pondus that counterpoised the Air S K this presently in stead of it raiseth 29 inches of Mercury from G to R. We see secondly that one pillat of Air can counterpoise another Fluids of diverse kinds interveening because the Air S K counterpoises the Air within the Pipe G O the VVater K P first interveening the Air P H next interveening and the stagnant and suspended Mercury interveening also We see thirdly from this eighth trial that the Pressure of the Atmosphere may be communicated thorow diverse kinds of Fluids without the least diminution of its weight because the weight of the Pillar of Air S K is communicated and sent down thorow the Water K I thorow the Air P H thorow the VVater H B thorow the stagnant Mercury B D and up thorow the suspended Mercury B G till it suspend the 29 inches between G and R which is the just counterballance of it We see moreover that Fluids counterpoise one another according to altitude only and not according to thickness and breadth by comparing the Water K I that 's but half an inch thick to the Mercury B G that 's a whole inch thick We see from the last trial that when a Fluid is necessitated to counterpoise a Fluid of another kind in stead of a Fluid of its own kind it sustains no more of it than what is the just weight of the Fluid of its own kind because the VVater K I being under a necessity to counterpoise the Mercury B G in stead of so much VVater as would fill the Tub it sustains no more of it than the just weight of so much VVater as is said We see secondly that when two Fluids of divers kinds do counterpoise one another that which is heaviest in speciè hath alwayes the shortest Cylinder Next that the difference between their altitudes is most exactly according to the difference between their natural weights therefore B G is 14 times lower than B O because Mercury is 14 times heavier than VVater We see moreover that though two Cylinders of a Fluid can counterpoise one another in the Natural Ballance such as this Engine is yet they will not do it in the Artificial Ballance because though B G counterpoise K I in this Ballance yet in a pair of Scales the Mercury will be as heavy again as the VVater We see lastly that notwithstanding of this yet such a thing may be for if the orifice I were made as wide as the orifice F that the Cylinder K I might be equal to the Mercury B G in thickness then surely the one would counterpoise the other in the Libra or Artificial Ballance EXPERIMENT XV. Figure 21. THis Schematism represents a Water 72 foot deep as C D A B together with a crooked Pipe of glass I N H the one half whereof is I P 56 inches high and one inch wide the other half is P N R H of a
much Mercury as would fill between X O and Z F. For understanding the third remember as was noted before that Fluid Bodies counterpoise one another only according to altitude therefore 't is no matter whether the Tubs be wide or narrow If it be enquired how can one and the â—ame Water counterpoise two Fluids of different weights To say that Fluids counterpoise one another according to altitude doth not clear the difficulty for it still remains to be asked why they counterpoise one another after this manner Therefore it seems that if the Water raise the Mercury from C to E in the wide Pipe it must raise it in the narrow one from D to K. For answer consider first that as there are here two Pillars of Mercury C E and D G within the two Tubs so there are here also two Pillars of Mercury A P and B Q under the two orifices upon which the said two Pillars stand and rest Consider secondly that the Potentia or force of the Pillar A P is just equal to the Pondus of the Pillar E C A Item that the Potentia of the Pillar B Q is equal to the Pondus G D B. Thirdly that the Potentia of A P. is most exactly equal to the Potentia of B Q and the reason is because their tops A and B are parts of the same horizontal surface I say then if A P be equal to E C A and B Q equal to G D B and A P and B Q equal among themselves then must E C A be equal to G D B. The same Water then doth not counterpoise two Bodies of different weight I grant E C A to be far heavier than G D B while they are weighed in a pair of scales but the one is not heavier than the other as they are weighed in this ballance of nature From what is said we see first that in VVater there is a Pressure and a considerable weight This is evident from the rising of the Mercury VVe see secondly that Fluids counterpoise one another only according to Altitude Thirdly that when a lighter Fluid presseth up a heavier there is no more prest up of it than is the just weight of the pressing Fluid because the Mercury E C is just the weight of the VVater that presseth upon X Y O. That 's to say the part of the surface C is no more prest with the Mercury E C than the part X is prest with the VVater L Z X. Fourthly if Mercury were 28 times heavier than VVater only three inches would be prest up if it were but seven times heavier the altitude would be at S 12 inches above C. Fifthly it 's as easie for a large part of a surface to sustain a large Pillar as 't is for a narrow part to sustain a narrower Pillar because A P sustains E C A as easily as B Q sustains G D B. Sixthly that in Fluids there is a pondus and a potentia as is clear from the potentia of A P that sustains the pondus of E C A. The VVater likewise that sustains hath a potentia and the Mercury E C is the pondus of it Seventhly that there is alwayes equality of weight between the pondus and the potentia So is the potentia of A P equal to the pondus E C A. Eighthly that the pondus begets the potentia So the weight of the VVater begets the potentia that's in A P. For make this VVater deeper and you augment the potentia of A P. If you subtract from it the potentia of A P grows less by proportion Or the weight of E C A may be said to beget the potentia of A P. To proceed a little further let us suppose the Air H E to be removed In this case the Mercury rises 29 inches higher than E or 35 above C even as high as S. In the narrow Tub it will climb up to K if you take away the Air I G. This comes to pass by vertue of the Pressure of the Atmosphere that rests upon L N. From this we gather ninthly that there is a counterpoise between the Air H E and the weight of the Air that rests upon L N and that a slender Pillar of Air is able to counterpoise a thicker for H E is far narrower than L N. Tenthly that the Pressure of the Air can be communicated thorow divers kinds of Fluids because the weight that rests upon L N is sent down thorow the VVater L Z X and down thorow the stagnant Mercury and thrusts up the Liquor from A to S 35 inches Eleventhly that a lighter Fluid may be made to press with greater burden than a Fluid naturally heavier because the weight of the Air upon L N raises 29 inches of Mercury but the VVater raises only six VVe see twelfthly that Fluids have a sphere of activity to which they are able to press up themselves or Fluids of different kinds because first the stagnant Mercury can raise it self no higher within the Pipe than it is without Next the 84 inches of Water can raise the Mercury no higher than E. Lastly the weight of the Atmosphere can raise the Mercury no higher than S 29 inches above E. For another trial take out from among the Water the two Pipes and stopping closely the two under orifices fill them with Mercury to the brim Then thrust them down as before and open the said two orifices while they are below the surface X Y O and you will find the whole Cylinder fall down from H to E and there halt and the whole Cylinder in the narrow Pipe falls down from I to G. Or if you please before this be done stop closely the orifice H and the orifice I and you will find the Mercury go no further down than S by opening the orifice A and no further down than K by opening the orifice B. This leads us to a clear discovery of the reason why the Mercury subsides and sinks down from the top of the Tub in the Baroscope to the 29th inch whatever the diameter of the Pipe be And this lets us see that the Mercurial Cylinder is suspended by the Air after the same manner that the Mercury E C is suspended after and that there is no more difficulty in the one than in the other EXPERIMENT XVII Figure 23 24. THis Schematism represents a Water 30 fathom deep Under the first surface A there are six imaginary as B C D E F G every one whereof is five fathom below another There are here likewise two Glasses each one 12 inches high and 5 inches broad like unto these wherein Wine Sack or Brandy is preserved The Glass G M hath its orifice G upward The other Glass is compleatly open below without a narrow orifice For making Experiment take a long chord as long as the Water is in deepness and knit the end of it round about the neck of the Glass at G. Take another line of the same length and
Air comes out The reason is the same namely less Pressure in E than in F therefore when the inclosed Air that hath five degrees of Bensil comes to E that hath but four it must overcome and so long must it be victorious till by expanding it self it be reduced to the Bensil of four In pulling up the Glass from E to D more Air yet breaks out because a surface of three degrees of Pressure is not able to resist four degrees of Bensil In passing from D to C more Air comes yet out for the same reason till in going up to the top where there is no Pressure no more Air breaks out 'T is to be observed first that the motion of the Air up thorow the Water is but slow the medium being thick and gross Secondly that if the Glass be pulled up quickly from one surface to another or contrariwise let down quickly it presently breaks in pieces This comes to pass through the strong Bensil of the inclosed Air that must have time to expand it self otherwise it breaks out at the nearest for it being of six degrees of Bensil and coming quickly to a surface of five there happens an unequal Pressure the sides of the Glass being thrust out with greater force than they are thrust in with But if so be the Glass move slowly up the inclosed Air gets time to thrust it self out by degrees so that whatever surface the Glass comes to there is little difference between the Pressure of the Water and the Bensil of the Air. The reason why the Glass breaks in pieces while it goes quickly down is likewayes unequal Pressure upon the sides for in passing quickly from a surface of five degrees to a surface of six the sides are prest in with greater force than they are prest out with and the reason is because through the straitness of the hole G the Water cannot win in soon enough to make as much Pressure within as there is without 'T is to be observed thirdly that if the orifice G be stopped before that the Glass be sent down it will not go beyond three or four fathom when it shall be broken in pieces though the motion were never so slow and this comes to pass through the strong Pressure of the Water Fourthly the stronger the Glass be in the sides it goes the further down without breaking therefore a round Glass Bottle will sink 20 or 30 fathom before that it be broken with the Pressure of the Water If a Vessel of iron were sent down it ought to go much further An empty Cask or Hogshâ—ad will not sink beyond seven or eight fathom without breaking or bursting yet a Bladder full of wind knit about the neck with a Pack-Threed will go down 100 fathom yea 1000 without bursting It may be here inquired what sort of proportion is keeped by the unequal ingress of the Water I answer it may be known after this manner Let first down the Glass one fathom and having pulled it up again measure the deepness of the Water in the bottom of it Next having poured out that Water let it down two fathom and pulling it up measure the deepness which you will find more than afore Do after this manner the third time and the fourth time till you come to the lowest fathom and you will find the true proportion From what is said we see first that in Water there is a Pressure because through the force and power of this Water the 12 inches of Air that filled the Glass are reduced to three Secondly that this Pressure growes as the Water growes in deepness because there is more Pressure in B than in A more in C than in B and Io downward Thirdly that when Air is comprest by some extrinseck weight the Bensil is intended and grows stronger by unequal proportion as is clear from the unequal divisions 1 2 2 4 5 6. Fourthly two Fluids cannot cease from motion so long as the potentia of the one is unequal to the poâ—dâ—s of the other this is evident from the Water 's creeping in at G all the while the Glass is in going down and from the Air 's coming out all the while the Glass is in coming up Fifthly that no sooner two Fluids come to equality of weight but as soon the motion ends because if the Glass halt at D E or F in the going down upon which follows a counterpoise then doth the creeping in of the Water cease Sixthly there may be as much Pressure in a small quantity of a Fluid as in the greatest because there is as much Bensil in the small portion of Air included between K and G as there is of Pressure and weight in this whole Water that 's 30 fathom deep Seventhly that the Pressure of a Fluid is a thing really distinct from the natural weight this is evident from the Pressure of the inclosed Air G K that 's more and less as the Pressure of the Water K M is more and less but the natural weight is still the same seing the same quantity remains Eighthly one part of a Fluid cannot be under Pressure but the next adjacent must be under the same degree of Pressure this is also clear because what ever degree of bensil the included Air K G is under the Water K M is under the same Therefore when the one is under six as in the lowest fathom the other is under six likewise And when the one is under five degrees of Pressure as in the surface F the other is under as much Ninthly Bensil and Pressure are equivalent to weight because the Water K M is as much burdened with the Bensil of that small portion of Air above it as if it had a Pillar of Water 30 fathom high upon it Tenthly that the Pressure of Fluids is most uniform and equal and that two Fluids of different kinds may press as uniformly as if they were but one this is evident from the sides of the Glass that are not broken in pieces by the strong Bensil of the inclosed Air and heavy Pressure of the inclosed Water and this happens because the Pressure without is as strong as the Pressure within We see lastly that Water does not weigh in Water because when a man lets down this Glass by the chord to the lowest surface he finds not the weight of the Water K M that 's within the Glass but only the weight of the Lead Q. 'T is certain he finds not the weight of the Water I H because it rests not upon the Glass within but is sustained by ' its own surface the mouth of the Glass being downward and open When I say Water does not weigh in Water the meaning is not that Water wants weight or Pressure in it but that this weight and Pressure is not found as the weight and Pressure of other bodies are found while they are weighed in Water For example a piece of Lead or Gold hung in the Water by a
string the other end being fastened to a Ballance in the Air gravitats and weighs down the Scale and the reason is because Lead and Gold are naturally and specifically heavier than VVater but a piece of Metal of the same specifick weight with Water or VVater it self cannot gravitat in VVater or weigh down the Scale of a Ballance and the reason is because the surface of Water upon which they rest bears them up with as great weight and force as they press down with If it be said that the Water K M rests upon the bottom of the Glass within and therefore if the man above find the weight of the Glass he must find the weight of the Water within it I answer the consequence is bad because the weight of the Water within is sustained and counterpoised by the weight of the Water without whereupon the bottom of the Glass rests That 's to say as there is a Pillar of Water K M within the Glass that presseth down the bottom so there is a Pillar of Water without the Glass whereupon the bottom of the Glass rests and which bears up both But the greater difficulty is this the further down the Glass goes it grows the heavier because of more and more Water that creeps in at G. Now 't is certain the weight Q grows not heavier therefore it must be the Water within the Glass that makes the increase of the weight and therefore Water must still weigh in VVater If this argument had any strength in it it would prove the weight of the VVater I H to gravitat and weigh likewise because the further down this glass goes it grows the heavier because of more and more Water that creeps up from H to I. Now 't is certain the weight of Lead B grows not heavier Behold the difficulty is the same in both and yet it were rashness to affirm the Water I H to be found by a mans hand when he pulls up the Glass with a string seing it is sustained by its own surface and not by any part of the Glass Though this might suffice for an answer yet because the contrary is mantained by some and that with a new Experiment to prove it I shall be at some more pains to vindicat the truth of what I have said This new Experiment to prove that Water weighs in Water I found in a Philosophical Transaction of August 16. Anno 1669. Numb 50 the Invention whereof is attributed by the publisher to that honorable and worthy Person Mr. Boyl whose conclusions and trials I never much called in question but finding this opposite and contrary to what I have demonstrated I shall crave liberty to say amicus Socrates amicus Plato sed magis amica veritas and shall therefore examine it as briefly as may be The words of the Publisher are as follows The Author of this Invention is the Noble Robert Boyl who was pleased to comply with our desires of communicating it in English to the curious in England as by inserting the same in the Latine Translation of his Hydrostatical Paradoxes he hath gratified the Ingenious abroad And it will doubtless be the more welcome for as much as no body we know of hath so much as attempted to determine how much Water may weigh in Water and possibly if such a Problem had been proposed it would have been judged impracticable The Method or Expedient he made use of to perform it as near as he could may easily be learned by the ensuing accompt of a Trial or two he made for that purpose which among his Notes he caused to be registred in the following words A Glass-bubble of about the bigness of a Pullets egg was purposely blown at the flame of a Lamp with a somewhat long stem turned up at the end that it might the more conveniently be broken off This Bubble being well heated to rarify the Air and thereby drive out a good part of it was nimbly sealed at the end and by the help of the Figure of the stem was by a convenient Weight of Lead depressed under Water the Lead and Glass being tyed by a string to a Scale of a good Ballance in whose other there was put so much weight as sufficed to counterpoise the Bubble as it hung freely in the midst of the Water Then with a long Iron Forceps I carefully broke off the seal'd end of the Bubble under Water so as no Bubble of Air appear'd to emerge or escape through the Water but the Liquor by the weight of the Atmosphere sprung into the un-replenish'd part of the Glass-Bubble and fill'd the whole cavity about half full and presently as I foretold the Bubble subsided and made the Scale 't was fastned to preponderate so much that there needed 4 drachms and 38 grains to reduce the Ballance to an equilibrium Then taking out the Bubble with the Water in it we did by the help of a flame of a Candle warily applyed drive out the Water which otherwise is not easily excluded at a very narrow stem into a Glass counterpoised before and we found it as we expected to weigh about four drachms and 30 grains besides some little that remained in the Egg and some small matter that might have been rarified into vapors which added to the piece of Glass that was broken off under Water and lost there might very well amount to 7 or 8 grains By which it appears not only that Water hath some weight in Water but that it weighs very near or altogether as much in Water as the self same portion of Liquor would weigh in the Air. The same day we repeated the Experiment with another sealed Bubble larger then the former being as big as a great Hens-egg and having bâ—oken this under Water it grew heavier by 7. drachms and 34 grains and having taken out the Bubble and driven out the Water into a counter pois'd Glass we found the transvasated Liquor to amount to the same weight abating 6 or 7 grains which it might well have lost upon such accompts as have been newly mentioned Thus he Figure 24. THe design then of this Experiment is to prove that water weighs in Water but it seems there is here a very great mistake which I shall make out after this manner For which cause let this Schematism 24 represent the Experiment already described The â—lass-bubble then is E P F R. The stem is H C the weight that sinks the Glass is B. The surface of Water under which it is drowned is A D. The Ballance to which the Glass is knit by a string is N O. And lastly E F R is the Water that came in and filled the half of the Bubble Now I say it is not the weight of the Water E F R that turnes the Scales above and makes an alteration in the Ballance but ' its only the weight of the Lead B that does it For evincing this consider that all heavy bodies are either lighter in specie than Water
as corkâ— or of the same specifick weight with it as some Wood is or lastâ—y heavier in specie than Water as Lead or Gold Now 't is certain that bodies of the first sort cannot weigh in Water and the reason is because they being naturally lighter their whole weight is supported by the Water and therefore not one part of them can be born up by a Ballance above A piece of Cork that weighs 12 ounces in the Air weighs nothing in Water because as soon as it toucheth the surface the whole weight of it is supported and therefore cannot affect the Ballance above But bodies of the third sort as is clear from experience and reason does really weigh in Water And the reason is because they being naturally heavier than water their whole weight cannot be supported by it and therefore some part of them must burden the Ballance to which the body is knit A piece of Lead that weighs 12 ounces in the Air will not lose above 2 ounces when ' its weighed in Water or may be less But here there is no difficulty The question then is in order to bodies of the same specifick weight with Water as some Wood is or as Water is I say of such also that they cannot weigh in Water and the reason is because they being â—ust of the same weight must have their whole weight supported by it even as one foot of Water supports the whole weight of the foot above it It may be evidenced after this manner Take a piece of Wood that 's lighter in specie than Water and add weight to it by degrees till it become of the same weight with Water Knit it with a string to a Ballance ond weigh it in Water and you will find the whole weight supported by the Water And the reason is because being left to it self it can go no further down than till the upper part of it be level with the surface of the Water Now the whole weight being thus supported not one ounce of it can burden the Ballance In a word the Ballance can never be burdened unless the body that 's knit to it have an inclination to go to the ground when left to it self which a body of the same weight with Water can never have I conclude then if a body of the same weight with Water cannot weigh in Water neither can Water weigh in Water seing Water is of the same weight with Water And Therefore the Water E F R that 's now within the Bubble cannot in anywise burden the Ballance above but must be supported wholly by the Water I K G H upon which the bottom of the Glass rests If it be said that the Glass it self is supported by the Ballance because ' it s heavier in specie than Water therefore the VVater within that rests upon the sides of it must be supported likewise by it I answer the whole weight of the Glass is not supported by the Ballance but only a part the VVater I K G H supporting the other part And this part is just as much as is the weight of VVater that 's expelled by the Glass Now if the said VVater support so much of the Glass because it is the just weight of so much VVater why should it not also support the VVater within the Glass Seing the VVater within the Glass is just the weight of as much VVater as will fill the space E F R. I come in the next place to shew that it is the weight of the Lead B that turns the Scales when the VVater comes in at C and fills the half of the sphere For understanding this let us suppose first the weight that 's in the Scale O to weigh six ounces Secondly that the Glass takes 12 ounces to sink it compleatly under the surface A D. Thirdly the weight B to be 18 ounces namely for this cause first that 12 of it may sink the Glass next that the other six may counterpoise the six in the Scale O. Lastly that the VVater within the Glass weighs six ounces I abstract from the weight of the Glass it self which is not considerable seing the most part of it is supported by the VVater and not by the Ballance Now I say 't is six ounces of the weight B that makes this alteration and turnes the Scales For if 12 ounces sink the Glass below the VVater when ' its full of Air and no Water in it then surely â—ix are sufficient to sink it when it is half full And the reason is because there is a less Potentia or force in six inches of Air by the one half to counterpoise a weight of 12 ounces than in 12 inches of Air. Therefore this Air being reduced from 12 inches to six it must take only six ounces to sink it If this be then the other six ounces that now wants a party to counterpoise them must burden the Ballance and be supported by the Scale and therefore to make a new equipondium again you must make the weight O 12 ounces by adding six to it that it may counterpoise 12 of B the other six being counterpoised by the Air E P F. Let us suppose next this Glass to be compleatly full of VVater and the whole Air expelled In this case the Scale O must have 18 ounces in it for making a new equipâ—ndium The reason is because there being no Air in the Glass to counterpoise any part of B the whole weight of it must be sustained by the Ballance and therefore in the Scale O there must be 18. Now I enquire whether these 18 ounces are the equipondium of the VVater within the Glass or of the weight of Lead B 'T is impossible it can counterpoise them both seing the VVater is now 12 and B 18. It must then either be the counterballance of the Water or the counterballance of the Lead It cannot be the first because 12 cannot be in equipondio with 18 It must then be the second Or if these 18 ounces in the Scale O be the counterpoise of the Water within the Glass I enquire what sustains the weight of the Lead B The weight of it cannot be sustained by the Water because 't is a body naturally heavier than Water it must therefore be sustained by the Ballance I conclude then that Water cannot weigh in Water If it be objected that this conclusion seems to contradict and oppose the Pressure of the Water that 's been hitherto confirmed with so many Experiments I answer the Pressure of the Water is one thing and Water to weigh in Water is another The first is when one Pillar of Water counterpoises another or when a Pillar of Water counterpoises a Pillar of Mercury or is counterpoised by a Pillar of Air all which is in order to the Natural Ballance wherein bodies weigh only according to altitude The second is when VVater is not counterpoised by VVater or by Mercury or by Air or by any other Fluid but when ' its weighed by
Pressure that 's in the VVater not only 10 but 20 or 30 fathom without all hazard And the reason is because what Pressure soever is without to press in the sides the same degree of Pressure is within to press them out By this means there is not one part of the VVater how deep soever to which the Ark may come down but there will be found as much force in the Air within as will counterballance the whole weight without as will be infallibly demonstrated afterwards This answers a fourth objection namely if holes be cut out in the sides of the Ark in stead of windows the force of the VVater will break the Glasses in pieces that covers them There is here no hazard though the said windows were 12 inches in Diameter but it s not needful they be so large It 's sufficient if they be 2 inches wide for a mans eye near to a hole 2 inches wide will see a great way about him There 's a necessity the Glasses be joyned in with cement that Water may not have access to come in or Air to go out In such a case ther 's no hazard that the Pressure of the VVater will break through the windows or break the Glasses because the Pressure of the Air within being of the same force with the strength of the VVater without the Glasses are keeped intire It may be enquired what hazard would follow upon supposition a small hole were pierced in the head of the Ark above when it is going down I answer ther 's not so much hazard as a man would think provided the hole be not wide but narrow If it be wide not only the VVater comes in but the Air goes out the one thrusting it self by the other If the hole be no wider than the point of a bodkin is in thickness ther 's no danger at all for by reason of the strait passage the one cannot thrust it self by the other and therefore neither the VVater can come in nor the Air go out And this comes to pass by reason that the Air within is as strong as the Water is without Now if they be both of the same strength and force why ought the Air rather to go out then the Water to come in or the Water rather to come in then the Air to go out I am confident though the hole were as wide as a man might thrust in his little finger yet no irruption of Water or eruption of Air would follow This demonstrats clearly that though a small rift or leak should happen in the Ark yet no hazard or danger would follow thereupon If it be inquired whither the greatest hazard is from the ingress of the Water or from the egress of the Air I answer ther 's no danger from the coming in of the Water from above because as it comes in it falls down and so mingles with the rest below But if the Air should go out the Ark fills presently full of Water and drowns the man that is in it The next thing considerable in this Diving Instrument is the foot-stool of Lead C D that 's not only useful for a man to set his feet upon when he dives but especially for sinking of the Ark. For this being made of Timber and full of Air cannot of ' its own accord go down unless it be pulled and forced by some weight It may either be broad and round or square if square a large foot over from side to side or 16 inches will determine the breadth By this means it will happen to be pretty thick seing a great quantity of Lead is required In each corner there must be a hole for four chords by which it is appended to the mouth of the Ark. Between it and the roof within must be the height of a man and more The weight of it cannot be well determined without trial seing it depends upon the dimensions of the Ark. First then try how much weight will bring the top E F G H level with the surface of the Water When this is found add a little more weight till it begin to sink and this will surely take it to the ground though it were 40 fathom 'T is to be observed that when the top E F is level with the surface there is here a just counterpoise namely between the Lead foot-stool on the one part as a pondus and the Ark on the other part as a potentia for with what force the Ark endeavours to pull up the Lead with the same force strives the Lead to pull down the Ark. Hence it is that as a small weight will turn a pair of Scales when they are in equilibrio so a small weight added to the foot-stool will sink the Ark. Though it may seem difficult to determine the just weight of the foot-stool without trial as I said yet I purpose to essay it For this cause consider that there is no Vessel of VVood almost if it be once full of Water but the orifice of it will ly level with the surface of the VVater wherein it sweems This proposition is so evident from experience that it needs no confirmation From this I gather that as much weight of Lead or Stone will bring the top of the Ark E F G H level with the surface of the VVater as is the weight of the Water that fills it If you suppose then the Ark to be 36 inches broad and 40 inches high it must contain 30 cubique foot of Water Now supposing each square foot of this Water to weigh 56 pound 30 foot must weigh 1680 pound This is gathered from trial and experience for after exact search I found a cubique foot of Water in bulk about 16 pints of our measure to weigh 56 pound Take then a piece of Lead of that weight and you will find it make a just counterpoise with the Ark. If any be desirous to know the quantity of it I answer if lead be 13 times naturally heavier then Water you will find that a piece of Lead about 16 inches every way will do it If it be objected that when a mans body is within the Ark the weight of the foot-stool must be less even as much less as is the weight of the man whom I suppose to weigh 224 pound or 14 stone I answer the whole weight of the man is not to be deduced from the foot-stool but the one half only and the reason is because a mans body being of the same specifick and natural weight with Water it cannot preponderat or weigh in VVater because magnitudes only naturally heavier then VVater weigh in VVater as Lead or Stone therefore seing the one half of the man is within the Ark and the other without among the Water that part only must weigh that 's invironed with Air. This may seem a plausible answer and might do much to satisfy these that are not very inquisitive yet being examined it will be found unsufficient Therefore I say there 's
not one part of the mans body that weighs within the Ark or makes it heavier Yet I affirm that when the mans body is within the Ark a less weight will sink it then when his body is out of it even as much less than before as is the just weight of the one half of the man For example if 1680 pound be the just counterpoise of it without the Man then after the Man is in it it will take only 1568 pound to counterballance it supposing the one half of the man to weigh 112 pound or seven stone yet it is not the weight of the man that makes this difference For understanding what 's the cause of this alteration consider that when a mans body is within the Ark there is less Air in it then while his body is out of it even as much less in quantity as the bulk of the parts are that are within If this be then must the Ark become heavier not because the mans body makes it heavier but because there is less Air in the Ark then before and therefore there arises an inequality between the weight of the foot-stool and the weight or rather lightness of the Ark. For if 1680 pound of Lead was the just counterballance of it when it had 30 cubique foot of Air within it it must exceed when there is less Air in it But there occures here two difficulties the first is what 's the reason why as much weight must be deduced from the foot-stool as is the the precise weight of the one half of the man Secondly how shall we come to the true knowledge of that weight that is to know distinctly how many pounds or ounces it is of For answer let us suppose that the one half of the man is just as heavy as so much Water equal in bulk to his own half This may be granted without scruple seing a mans body is judged to be of the same specifick and natural weight with Water and though there should be some small difference yet it will not make or produce any insufficiency in the argument for these demonstrations are not Mathematical but Physical Therefore as much Water in bulk as is equal to that part of the man that is within the Ark must be as heavy as the half of the man Now supposing the half of the man to weigh 112 pound and consequently that Water to weigh as much I affirm the said Water to contain 3456 cubique inches but 3456 cubique inches makes exactly two cubique feet which I gather thus Seven pound of Water requires 216 cubique inches because a Cube of six inches weighs exactly seven pound therefore according to the rule of proportion 112 pound will require 3456 inches which amounts to two cubique foot The Ark then by receiving the one half of the mans body loseth two cubique foot of Air therefore if 30 foot of Air require 1680 pound weight of Lead to counterpoise it 28 foot of Air must require only 1568 pound therefore to make a new counterballance you must deduce 112 pound from the foot-stool This answers both the difficulties If it be said that the foot-stool weighs less in VVater than in Air therefore it must be heavier then 1680 pound I answer 't is needful to abstract from that difference till the just calculation be once made and that being now done I say that a Cube of Lead 16 inches weighing 1680 pound If Lead be 13 times heavier than VVater will lose about 130 pound The reason is evident because a heavy body weighs as much less in VVater than in Air as is the weight of the Water it expells But so it is that a Cube of Lead of 16 inches expells a Cube of VVater 16 inches But a Cube of VVater 16 inches weighs 130 pound which I gather thus 216 inches or a Cube of six inches weighs seven pound therefore 4032 inches must weigh 130 pound For if 216 give 7,4032 must give 130. But to return Though there be small difficulty to let it down and to sink it 20 or 30 fathom yet there is no small difficulty to pull it up again And the reason is this because the further down it goes the Air within is the more contracted and thrust up by the Pressure of the Water towards the roof By this means though near the top of the Water there was little difference between the weight of the Lead and the Ark yet 9 or 10 fathom down the difference is great the weight of the one far exceeding the weight of the other and therefore there must be greater difficulty to pull it up from 10 fathom than from 5 and yet more difficulty from 20 than from 10. However yet 't is observable that as the Ark in going down becomes heavier and heavier so in coming up it growes lighter and lighter therefore less strength is required in pulling it up from the tenth to the fifth fathom than from the fifteenth to the tenth the reason is because in coming up the Air within expands it self and fills more space in the Ark which in effect makes it lighter and more able to overcome the weight of the Lead To make these things more evident let us suppose that when the Ark is down 18 or 20 fathom the Air to be contracted by the force of the Water from L M to P Q 12 inches Next that the weight of the foot-stool is 1680 pound Now if this weight was the just counterpoise of the Ark at the top of the Water then surely it must far exceed it now when it 's 20 fathom down because the Air that was 30 foot is now reduced to 21. Count then and you will find that if 30 require 1680 21 will only require 1176 therefore the weight of the Lead will exceed the weight of the Ark at 20 fathom deep by 504 pound This will be yet more evident if we consider that while the top of the Ark E F G H is level with the surface above the VVater thrust out of ' its own place by this bulk is just the weight of both Lead and Ark. But when ' its down 20 fathom and the Air reduced from L M to P Q there cannot be so much VVater expelled now as before seing the space L M P Q is full of VVater Now I say the Lead at 20 fathom must be exactly so much heavier than the Ark as is the weight of the said VVater L M P Q which in effect will be 504. pound for ' its a square body 36 inches in thickness and 12 in deepness The weight of the rope is likewise to be considered that lets down the Ark for the longer it be and more of it goes out it 's the heavier and more troublesome to pull up There is no way to cure this difficulty but by finding out a way how to keep a just counterpoise between the Lead and the Ark all the time it is in going down If the Air within did
not contract it self no difference would happen but this is impossible so long as the Water is under a Pressure The expedient then must be found out another way namely by kniting a small rope to the iron ring N in length with the other to which at certain distances relating to the fathoms the Ark goes down must be fastned empty little Vessels of Wood or bladders which by their lightness may compense the decrement and decreasing of the Air. First then let down the Ark three fathom and see how much it is heavier than before and as you find the difference so fasten to R one Bladder or two till the Ark be brought near to a counterpoise Secondly let it go down other three fathom and observe that difference also and accordingly fasten to T as many as will reduce the two to a counterpoise again Do after this manner till it sink 15 or 20 fathom 'T is to be observed that the further down the Ark goes the difference is the less therefore less addition will serve and the reason is because there is less Air contracted in passing between the fifth and the tenth fathom than in passing from the first to the fifth The proportion of contraction is represented by the unequal divisions within the mouth of the Ark as 1. 2. 3. 4. In a word by what proportion the decrement of the Air is by that same proportion must the addition be upon the rope S N. Suppose then the Air to be diminished four inches in going down four fathom which will be 5184 square inches or three square foot then surely as much Air must be added to the rope S N by bladders In going down as far let us suppose three-inches to be contracted then less will suffice Though it cannot be determined without trial how much Air is contracted in three fathom and how much in six and how much in nine yet this is sure that the decreasing is according to unequal divisions that 's to say less in six than in four less in 8 than in six and less in 10 than in 8 and so downward and that this is the rule namely according to what quantity the Air within the Ark is contracted according to that same measure must the addition of Air be to the rope If it be said that Bladders full of wind cannot go down thorow the VVater without bursting I answer 't is a mistake because their sides being pliable and not stiff like the sides of a Timber Vessel they yeeld and therefore cannot burst It 's observable that when a bladder goes far down the sides becomes flaccid and flagging In this case the Air that before had the forme of the Bladder and was somewhat ovall must now become perfectly globular and round for 't is sure that the dimensions of it are altered by the Pressure of the VVater namely from more quantity to less if this be then the form must be round seing the Pressure of the Water is most uniform even as drops of VVater or Rain from a house side are round upon this account This second way may be thought upon also Make the Leaden foot-stool that sinks the Ark not of one piece but of many that so when the Air within it begins to be contracted by degrees in going down a proportionable weight may be subtracted for keeping a just counterpoise all the while of the descent Or because the greatest trouble is in bringing of it up let the Diver when once he is at the bottom subtract so much weight from the foot-stool as he thinks will go near to make a counterpoise at that deepness For example if the weight of the foot-stool be 40 pound heavier than the Ark then let him subtract 30 or 36 which may ly and rest upon the ground till it be drawen up at a convenient time by a chord By his means it will be easie to move the Ark from one place to another Next there shall be little or no difficulty to pull it up Nay upon supposition the rope were broken by which it was let down yet if the Diver please he may come up without any mans help And this is most easily done namely by subtracting as much weight as will make the Ark the stronger party 'T is to be observed that when you are at the bottom and if you make the Lead but one pound lighter than the Ark it will surely come up and cannot stop by the way The reason is because a very small weight will turn the Scales between two bodies thus weighing in VVater Next the further the Ark comes up it becomes the lighter because the Air within it expands it self the more But leaving this let us come to explicat the reason why the contraction of the Air is not uniform but rather difform For if in going down three fathom three inches be contracted there will not be other three contracted in going down the second three but less and yet less in going down the third three Two things then are to be explicated here First why there is a contraction Next why it is after such a manner As for the first the contraction is caused by the Pressure of the Water which gradually increaseth from the top to the bottom as is clear from the last Experiment therefore there being a greater Pressure in a surface six fathom deep than in a surface three fathom deep the Air within the Ark must be more contracted in passing between the third and sixth than in passing between the first and third When I say more contracted the meaning is that more quantity is contracted to less whereby the Bensil of it is more intended or that the Air is more bended As for the second we must remember from the last Experiment that the cause of this is not from the VVater as if forsooth the Pressure of it were according to unequal proportion but from the Air it self whose kind and nature it is to suffer compression after such a way 'T is evident in Wind-guns whose second span of Air is comprest with greater difficulty than the first and the third with greater difficulty than the second 'T is so with all bodies endowed with Benfil for ay the longer you bend you find the greater difficulty As there is a great disadvantage to the man that Dives from the contraction of the Air so there is a great advantage to him from this manner and way of contraction for if it were uniform according to the Pressure of the Water then if three fathom comprest three inches six fathom ought to compresse six inches nine fathom nine inches and so forward till by going down either the whole Air should be comprest to no inches or else very little should remain for respiration The next thing to be taken notice of is that all the while during the down going of the Ark there is still equality of weight between the Pondus of the Water and the Potentia of the Air for with what
the Tub without but the Air F H is only equal to the Tub within I answer it is so indeed but here is a solution to the difficulty I do not find the whole weight of the Air L M but only as much of it as is equal to F H. Suppose the Tub to be 12 inches within from side to side and 16 without from side to side I say then I find only the burden of so much Air as answers to the cavity of the Tub because the rest of these inches are counterpoised by as much below namely by the Air that environs the orifice E for it 's supposed that if the Tub be two inches thick above it must be as thick in the lips So that the whole Tub is not unequally prest but only so much of it within upon the top as answers to the cavity Tenthly that when the Pipe is but half full of VVater namely from E to K I find only 952 pound of the Air L M though before I found 1904. The reason is because the one half of it is now counterpoised by the Air I G and therefore the weight of it becomes insensible 'T is clear from the sixth assertion that the Air I G presseth down with 952 therefore it must press up with as much seing according to the sixth Theorem the Pressure of a Fluid is on every side Eleventhly that when there is only eight foot of VVater and a half in the Tub namely between E and N I find only 476 pound of the Air L M. Because in this case the Air N G counterpoiseth 1428 pound of it For if the said Air burden the Water N E with 1428 pound as is clear from the seventh assertion it must likewise press up the Tub with as much and so counterpoise as much of the Air L M. Twelfthly that when there is nothing within the Pipe but Air the whole weight of the Air L M becomes insensible to me The reason is evident because it is wholly counterpoised by the Air within the Pipe I affirm thirteenthly that the VVater E G is in equilibrio with the Water A B that 's to say 1904 pound is in equilibrio with 476 pound I prove it evidently by the first medium all the parts of an Horizontal surface are equally prest therefore the part A sustains no more burden then the part E therefore A B is as heavy as E G and consequently the Air C D must be as heavy as the Air F H. Lest this proposition may seem to contradict what is already said I must distinguish a twofold Ballance according to the third Theorem one Natural another Artificial In the Artificial Ballance where magnitudes do weigh according to all their dimensions viz. Longitude Latitude and Profundity the Water A B and the Water E G are not in equilibrio together seing the one is 1428 pound heavier than the other But in the Ballance of Nature such as these Pipes are all the four makes an equipondium together because they do not weigh here according to their thickness but only according to their altitude Therefore seing A B is as high as E G and seing C D is as high as F H they must all be of the same weight From the first assertion I infer that one and the same Fluid even in the Ballance of Nature may sometimes be in equilibrio with a lesser weight and sometimes with a greater because the Air C D that weighs really 476 pound is in equilibrio with the Water A B that weighs but 168. This is when A B is supposed to be only 12 foot high It 's likewise in equilibrio with it when it s 34 foot high But how can A B that 's 12 foot high press A with as much weight as when it s 34 foot high I answer by a similitude when a Cylinder of Wood 12 foot high stands upon a Table it may burden it as much as if it were a Cylinder 34 foot high For supposing it to be thrust in between it and v. g. the ceiling of the room above it must press down with more weight then if it were not thrust in So this Cylinder of Water A B that 's but 12 foot high being prest between the surface A and the top of the Tub within must burden A as much as if it were 34 foot high for being of this hight it only stands upon the surface without pressing up the top of the Tub. I infer from the second assertion that each Pillar in a Fluid hath a determinate weight This is evident from the determinate weight of A B that weighs first 168 pound being 12 foot high and 467 pound being 34 foot high and so of the rest I infer secondly that the thicker and grosser a Pillar of a Fluid be it is the heavier even in the Artificial Ballance and contrariwise the more slender and thinner it be it is the lighter This is evident from the Water A B six inches thick that weighs 476 pound and from the Water E G 12 inches thick that weighs 1904 pound So doth the Pillar of Air C D weigh less then the Pillar F H. Here is ground for knowing the certain and determinate weight of a Pillar in any sort of a Fluid whatsoever As to Air its clear and evident that a four-square Pillar thereof 12 inches every way weighs 1904. That 's to say if it were possible to take the Pillar of Air F H in its whole length from the surface of the earth to the top of the Atmosphere and pour it into the Scale of a Ballance it would be exactly the weight of 1904 pound Here is a secret though that same Pillar of Air were no longer than 6 or 10 foot yet the Pressure of it upon the body it rests upon is equivalent to 1904 pound If this be you say what is the weight of Air that rests upon this Table that 's 36 inches square I answer it must be as heavy as a Pillar of Water 34 foot high and 36 inches thick which will by just reckoning amount to 17136 pound or to 1071 stone weight It may be inquired next what 's the weight of the Air that burdens the pavement of this parlour that 's 16 foot square I answer 487424 pound Because it is exactly the weight of a bulk of Water 34 foot high and 16 foot thick 'T is to be remembred that though the Pressure of it be so much yet being poured into the scale of a Ballance it will not weigh so much for not only as much as fills the room must be taken but as much as passeth from the pavement to the top of the Atmosphere According to this method 't is easie to determine the weight of any Pillar of Air whatsoever provided a man but once know the thickness of it both the wayes e. g. there 's a planum 12 inches long and six inches broad upon which rests a Pillar of Air. The weight of it then is just the burden of
an open Trade W. C. Hydrostatical THEOREMS Containing some useful Principles in order to that excellent Doctrine anent the wonderful Weight Force and Pressure of the Water in its own Element THEOREM I. In all Fluids besides the first and visible Horizontal surface there are many moe imaginary yet real Figure 1. FOR the better understanding the following Experiments it is needful to premit the subsequent Theorems the first whereof is that in all Fluid bodies such as Air Water and Mercury or any other liquid there is besides the first and visible surface innumerable moe imaginary under that first yet real as may be seen from the following Schematism which represents a Vessel full of Water where besides the first surface A B C D there is a second E F G H and a third I K L M and so downward till you come to the bottom This holds true not only in Water but in Air also or in any other Fluid body whatsoever I call the under-surfaces imaginary not because they are not real for true and real effects are performed by them but because they are not actually distinguished amongst themselves but only by the Intellect THEOREM II. In all Fluids as it is needful to conceive Horizontal Plains so it is needful to conceive Perpendicular Pillars cutting these Plains at right Angles Figure 1. THis Proposition is likewise needful for understanding the following Doctrine anent the Pressure of the Water for in it as in all Fluids though there be not Columes or Pillars actually divided reaching from the top to the bottom yet there are innumerable imaginary which do as really produce effects by their pressure as if they were actually distinguished These imaginary Pillars are represented in the first Schematism one whereof is A E I N O P Q the other B F K R T and so forth THEOREM III. There is a twofold Ballance one Natural another Artificial BY the Artificial Ballance I understand that which the Mechanicks call Libra which Merchants commonly use By the Natural Ballance which for distinctions cause I so nominat I mean v. g. a Siphoâ— or crooked Pipe wherein water naturally ascends or descends as high or low in the one Leg as in the other still keeping an evenness or likeness of weight THEOREM IV. Fluid bodies counterpoise one another in the Ballance of Nature according to their Altitude only THis Theorem will appear afterwards most evident while we pass through the several Experiments and it is of special use for explicating sundry difficulties that commonly occur in the Hydrostaticks The meaning of it is shortly this while two Cylinders of Water are in the opposite Scales of the Natural Ballance they do not counterpoise one another according to their thickness for though the one Pillar of Water be ten times thicker then the other and consequently heavier yet is it not able to press up the other that 's more slender and so lighter beyond its own hight and therefore they weigh only according to their Altitudes THEOREM V. In all Fluids there is a Pressure Figure 1. THis is true not only of the Elements of Air and Water while they are out of their own place as they speak but while they are in it For Air and Water being naturally indued with weight the second foot cannot be under the first unless it sustain it if this be it must necessarily be prest with its burden So this Water being naturally a heavy body the foot I cannot be under E unless it sustain it and be prest with the burden of it the foot N being burdened with them both From this Pressure which is in Air ariseth a certain sort of force and power which may be called Bensil by vertue whereof a little quantity of Air can expand and spread out it self to a very large quantity and may be extrinsick force be reduced to that small quantity again Though this expansive faculty be evident in Air yet it is scarcely discernable in Water unless it be in very deep parts near the bottom where the Pressure is great This Pressure is not of the same Degree in all the parts but is increased and augmented according to the deepness of the Air and Water for the Air upon the tops of Mountains and high places is thought to be of a less Pressure then in Valleys and Water is of a less Pressure ten or twelve foot from the top then twenty or thirty So is the Water N under a far less Pressure then the Water P or Q. THEOREM VI. The pressure of Fluids is on every side Figure 1. THe meaning is that Air and Water presseth not only downward but upward not to the right hand only but to the left also and every way So the foot of water K not only presseth down the foot R but presseth up the foot F yea presseth the foot I and the foot L with the same weight And the first imaginary surface is as much prest up by the water I K L M as it is prest down by the water E F G H. Upon this account it is that when a Sphere or Glob is suspended in the midle of Water or Air all the points of their surfaces are uniformly prest After this manner are our bodies prest with the invironing Air and the man that dives with the ambient and invironing Water THEOREM VII All the parts of a Fluid in the same Horizontal Line are equally prest Figure 1. THe meaning is that the foot I is no more prest then the foot K neither is the foot L more burdened then the foot M. The reason is because each of these feet sustains the same weight for E F G H are all of them of the same burden therefore all the parts of a Fluid in the same Horizontal surface are prest most equally This holds true in Air and Mercury or in any othâ—â— Liquid also THEOREM VIII The Pressure of Fluids seem to be according to Arithmetical Progression Figure 1. THe meaning is that if the first foot of Water have one Degree of Pressure in it the second must have only two and the third must have only three and so forth which appears from the Schematism for the first foot E having one Degree of weight and the second foot I having of its self as much and sustaining E it must have two Degrees and no more So the foot N sustaining two Degrees of Pressure from I and E must have the weight only of three Degrees O of four P of five It 's evident also from Experience for while by the Pressure of Water Mercury is suspended in a glass tub we find that as the first fourteen inches of Water sustains one inch of Mercury so the second fourteen inches sustains but two and the third but three But if the Pressure were according to Geometrical progression the third foot of Water ought to sustain four inches of Mercury the fourth eight the fifth sixteen c. which is contrary to Experience
that is specifically or naturally lighter then Water I say then it must ascend to the top B and the reason is because the quadrat foot of Water K is more prest upward then the quadrat foot of Water I or L is but this cannot be iâ— Fluid bodies unless motion follow thereupon I say it is more prest up because R being lighter then N or S it must press with greater force upon K then S can do upon L or N upon I. It is still to be remembred That Fluids presseth with as much strength upward as downward according to the sixth Theorem and that an Horizontal surfaceâ—doth as really suffer unequal Pressure from below as from above THEOREM XIV Bodies naturally lighter then Water swim upon the surface and top Figure 1. THe reason of this Proposition must be taken from the nature of an equipondium or equal weight For without doubt there is a counter-ballance between the Pressure of the Water and the weight of the body that swims To make this probable let us suppose there were a piece of Timber in form of a Cube six inches thick every way without weight In this case the under-surface of that four-squar'd body being applied to the surface of the Water A would ly closs upon it as one plain Table lyes upon the face of another without any pressure and it being void of weight the part of the surface A would be no more burdened then the next part B adjacent whence no motion would follow Here is no equipondium or counter-ballance Secondly let us suppose the said body to acquire two ounces of weight then it follows that it must subside and sink two inches below the surface A B C D and that so far till it come by vertue of its new acquired weight to a counter-ballance with the Pressure of the Water Which Pressure is nothing else but as much force or weight as is equivalent to the weight of Water that is thrust out of its own place by the subsiding and sinking of that body two inches Thirdly let us suppose the same body to acquire other two ounces of weight then must it subside other two inches Lastly let us suppose that it acquires six ounces of weight then it follows that the whole body sinks so far I mean till its upmost surface be in an Horizontal line with the surface of the Water A B C D. Here it swims also because the weight of it becomes just the weight of so much Water as it hath put out of its own place I say it must swim because if the Water I was able to sustain the Water E which is put from its own place surely it must be able to sustain that body also that did thrust it from its own place seing both are of the same weight namely six ounces In this case the body immerged and the water wherein it is drowned become of the same weight specifically seing bulk for bulk is of the same weight To make this body specifically or naturally heavier then Water and consequently to sink to the bottom nothing is required but to suppose that it acquires one ounce more of weight which done it presently goes down I being more burdened then K. Note by the way a twofold weight in heavy bodies one individual the other specifick and that two bodies agreeing in individual weight may differ in specifick weight So a pound of Lead and a pound of Cork agree individually because they are both 16. ounces but they differ specifically because the one is naturally heavier then the other THEOREM XV. No Body that flots above Water even though its upper surface be level with the surface of the Water can ever be made to swim between the top and the bottom Figure 1. FOr clearing this Proposition let us suppose F to be a four-square piece of Timber of the same specifick and natural weight with Water and consequently its upper surface to be level with the surface of the Water A B C D. I say then if it be prest down to R it shall arise thence and never rest till it be where it was namely in F. The reason seems to be this because the four-squar'd body of Water R is really heavier then the four-squar'd piece of Timber F. If this be true it follows of necessity that it must ascend for if the Timber existing in R be lighter then the Water R the Water T must be less prest then the Water O or the Water V whence according to the twelfth Theorem motion must follow Again if the Timber R existing in the Water R be lighter then the same Water is then must the Water K be more prest up then the Water I or L whence yet according to the same Theorem motion must follow If it be said that the Timber F is of the same weight with the Water R because it being equal in weight with the Water F which it hath thrust out of its own place it must also be equal in weight to the Water R seeing F and R being of the same dimensions are of the same weight There is no way to answer this difficulty unless I say the four-squar'd body of water R is really and truly heavier then the four-squar'd body of Water F. The reason seems to be because the Water R is under a greater Pressure then the Water F and by vertue of this greater Pressure there are really moe parts of Water in it then in F therefore it must be heavier Even as there are far moe parts of Air in one cubick foot near the Earth then in six or seven near the Atmosphere Hence it is that a pint of Water taken from the bottom of the Sea fourty fathom deep will be heavier I mean in a ballance then a pint taken from the surface Take notice that when the vessel is once full at the bottom the orifice must be closely stopped till it come to the top otherwise the parts that are compressed at the bottom namely by the weight of the superiour parts relaxes themselves before they come to the top THEOREM XVI It is not impossible for a body to be suspended between the surface and the bottom Figure 1. FOr understanding this suppose F to be a four-square piece of Timber which though it will not rest but at the surface A B C D yet may be made to go down of its own accord and rest at T namely by making it so much heavier as the Water T is heavier then the Water F. To know this difference which is not very practicable the Cube of Water T must be brought from its own place under the same degree of Pressure it hath and put into the Scale of a Ballance and weighed with the Cube of Water F put into the other Scale Now if the Water T be half an ounce heavier then the Water F then to make the Timber F hing in T it must be made half an ounce heavier There seems to be reason for it
the parts of Water for the foot of Water R cannot be under Pressure unless the Water S and N be under the same degree of it Though this be true of Fluids while all the parts lye in the same Horizontal surface yet to speak strictly it will not hold true of the parts scituated under divers surfaces for without question the foot of VVater T must be under four degrees of Pressure if the VVater R be under three And if the Air in the lowest story of a building be under six degrees of Bensil the Air in the highest story must be under five If a man would distinguish Metaphysically and subtilly he will find a difference of this kind not only between the first and second fathom of Air nearest to the Earth but between the first and second foot yea between the first and second inch and less much more in Water as to sense However it be yet the Theorem holds true for we find no difference sensible between the compression of Air in this room and the compression of Air in the next room above it no not with the Baroscope or Torricellian Experiment that discerns such differences accurately I judge it likewise to be true in order to the next adjacent parts of Fluids of different kinds for while a surface of Mercury is burdened with a Pillar of Water or a surface of Water with a Pillar of Air whatever degree of weight and Pressure is in the lowest parts of these Pillars the same is communicated entirely to the surfaces that sustains them So then there is as much force and power in the surface of any Water as there is Weight and Pressure in the lowest foot of any Pillar of Air that rests upon it otherwise the surface of Water would never be able to support the said Pillar for a surface of six degrees of force can never be able to sustain a a Pillar of Air of eight or ten degrees of weight THEOREM XXI The Pressure of Fluids may be as much in the least part as in the whole Figure 1. THis Theorem may seem hard yet it can be made manifest by many instances for albeit the quantity of Air that fills a Parlour be little in respect of the whole Element yet surely there is as much Pressure in it as in the whole because Experience shews that the Mercurial Cylinder in the Baroscope will be as well sustained in a Chamber as without and under the whole Atmosphere directly which could not be unless the small portion of Air that 's in this Parlour had as much Pressure in it as in the whole Element Besides this it will be found in a far less quantity for though the Baroscope were inclosed and imprisoned so closs within a small Vessel that the Air within could have no communion with the Air without yet the Pressure of that very small quantity will sustain 29. inches of Mercury and this will come to pass even though the whole Element of Air were annihilated This Proposition is likewise evident in order to the Pressure of the Water for put the case the Baroscope whose Mercurial Cylinder is 29. inches by the Pressure of the Air were sent down to the bottom of a Sea 34. foot deep within a Vessel as a Hogs-head and there exactly inclosed that the VVater within could have no commerce with the VVater without yet as well after this shutting up as before other 29. inches would be sustained by the Pressure of this imprisoned VVater which proves evidently that there is as much Pressure in one Hogs-head full of VVater at the bottom of the Sea as in the whole Element of VVater above or about for an Element of VVater never so spacious if it exceed not 34. foot in deepness can sustain no more Mercury then 29. inches by its Pressure Yea though the Vessel with the Baroscope and imprisoned VVater in it were brought above to the free Air yet will the VVater retain the same Pressure and will de facto sustain 29. inches of Mercury provided the Vessel be kept closs It is therefore evident that as much Pressure may be in one small quantity of VVater as in the whole Element or Ocean 'T is to be observed that this Theorem is to be understood chiefly of the lower parts of Fluids seing there cannot be so much Pressure in the VVater P as in the VVater Q for in effect there is as much Pressure in the VVater Q as is in the whole VVater above it or about it From this Theorem we see evidently that the Pressure and Bensil of a Fluid is not to be measured according to its bulk and quantity seing there is as much Bensil in one foot nay in one inch of Air as is in the whole Element and as strong a Pressure in one foot of VVater or less as there is in the whole Ocean therefore the greatest quantity of Air hath not alwayes the greatest Bensil neither the greatest quantity of VVater the greatest Pressure But this will appear more evident afterwards THEOREM XXII The Pressure and Bensil of a Fluid is a thing really distinct from the natural weight of a Fluid Figure 1. THis may be easily conceived for as in solid bodies the Bensil and natural weight are two distinct things so is it in Air and Water or in any other Fluid The weight of a Bow is one thing and the natural weight of it is another The weight of the Spring of a Watch and the Bensil of it are two distinct things The weight perhaps will not exceed two ounces but the Bensil may be will be equivalent to two pound Though these may illustrate yet they do not convince therefore I shall adduce a reason and it 's this The natural weight of a Fluid is less or more as the quantity is less or more but it is not so with the Pressure because there may be as much Pressure in a small quantity as in a great as is evident from the last Theorem therefore they may be different The first part of the Argument is manifest because there is more weight in a gallon of Water then in a pint A second reason is because a Fluid may lose of its pressure without losing of its weight This is evident from the Schematism for if you take away the four foot of Water E F G H and consequently make the four Pillars shorter the foot of Water Q becomes of less Pressure but not of less Weight seeing the quantity still remains the same at least the loss of weight is not comparable to the loss of Pressure I say it becomes of less Pressure because there is a less burden above it Thirdly the Pressure and Bensil may be intended and made stronger without any alteration in the weight so is the Bensil of Air within a Bladder made stronger by heat without any alteration in the weight of it Likewise the Pressure of the foot of Water Q may be made stronger by making these four
pillars higher without any alteration at least considerable in the weight for it still remains a foot of water whatever be the hight of the pillars above it Lastly the weight of a Fluid is essential to it but the Pressure is only accidental because it is only generated and begotten in the inferiour parts by the weight of the superiour which weight may be taken away THEOREM XXIII Though the Bensil of a Fluid be not the same thing formally with the weight yet are they the same effectively THis proposition is true in order to many other things besides Fluids for we see that the Sun and Fire are formally different yet they may be the same effectively because the same effects that are done by the heat of the Sun may be done by the heat of the Fire So the same effects that are produced by the weight of a Fluid may be done by the Pressure and Bensill of it Thus the Mercurial Cylinder in the Torricellian Experiment may be either sustained by the Bensil of the Air or the weight of it By the Bensil as when no more Air is admitted to rest upon the stagnant Mercury then three or four inches the rest being secluded by stopping the orifice of the Vessel By the weight of it as when an intire Pillar of Air from the top of the Atmosphere rests upon the face of the stagnant Quicksilver It is also evident in a Clock which may be made to move either by a weight of Lead or by the force and power of a Steel Spring THEOREM XXIV The surfaces of Waters are able to sustain any weight whatsoever provided that weight press equally and uniformly Figure 1. THis is evident because the imaginary surface of VVater O T V X doth really support the whole sixteen Cubes of VVater above it yea though they were sixteen thousand And the reason is because they press most equally and uniformly VVhat I affirm of the imaginary surface the same I affirm of the first and visible For let a plain body of lead never so heavy be laid upon the top of the VVater A B C D yet will it support it and keep it from sinking provided it press uniformly all the parts of that surface It is clear also from the subsequent Theorem THEOREM XXV The surfaces of all Waters whatsoever support as much weight from the Air as if they had the weight of thirty four foot of Water above them or twenty nine inches of Quick-silver pressing them THis Proposition is evident from this that the Pressure of the Air is able to raise above the surface of any Water a Pillar of Water thirty four foot high For put the case there were a Pump fourty foot high erected among stagnant Water and a Sucker in it for extracting the internal Air a man will find that the Water will climb up in it four and thirty foot which Phenomenon could never happen unless the surface of the stagnant Water among which the end of the Pump is drowned were as much prest with the Air as if it had a burden of Water upon it thirty four foot high The second part is also evident because if a man drown the end of a long Pipe in a Vessel with stagnant Quick-silver and remove the Air that 's within the Pipe by a Sucker or more easily by the help of the Air-pump he will find the Liquor to rise twenty nine inches above the surface below which thing could never come to pass unless the Pressure of the Air upon the surfaces of all Bodies were equivalent to the Pressure and weight of twenty nine inches of Quick-silver THEOREM XXVI All Fluid Bodies have a sphere of Activity to which they are able to press up themselves or another Fluid and no further which is less or more according to the altitude of the pressing Fluid Figure 2. FOr understanding this Proposition let us imagine G H C D to be a Vessel in whose bottom there are five inches of Mercury E F C D. Next that above the stagnant Mercury there are thirty four foot of Water resting namely A B E F. Lastly that upon the surface of the said Water there is resting the Element of Air G H A B whose top G H I reckon to be about six thousand fathom above A B. Besides these let us imagine that there are here three Pipes open at both ends the first whereof C A G having it 's lower orifice C drowned among the stagnant Mercury E F C D goeth so high that theu pper orifice goeth above the top of the Air G H. The second whose lower orifice I is only drowned among the Water A B E F reaches to the top of the Air likewise The third whose open end K is above the surface of the VVater A N B and hanging in the open Air goeth likewise above the Atmosphere These things being supposed we see that no Fluid can by its own proper weight press any part of it self higher then it 's own surface seing the stagnant Mercury E F C D cannot press it self within the Pipe C G higher then E. Neither can the VVater A B E F press it self higher within the Pipe I L then the point N. Lastly neither can the Air G H A B press it self within the Pipe K M higher then M. But when one Fluid presseth upon another as the VVater A B E F upon the Mercury E F C D then doth the said Mercury ascend higher than it 's own surface namely from E to O which point is the highest to which the thirty four foot of VVater A B E F can raise the Mercury which altitude is twenty nine inches above the surface E I F. But if a second Fluid be superadded as the whole Air G H A B then must the Mercury according to that new Pressure rise by proportion so rises the Mercury from O to P other twenty nine inches By this same additional weight of Air the Water rises thirty four foot in the Pipe I L namely from N to R. Now I say the outmost and highest point to which the Element of Air G H A B can raise the Mercury is from O to P for by the Pressure of the Water A B E F it rises from E to O. And the highest point to which the said Air can raise the VVater is from N to R. The reasons of these determinate altitudes must be sought for from the altitudes of the incumbing and pressing Fluids for as these are less or more so is the altitude of the Mercury and of the VVater within the Pipes more or less The hight therefore of the Mercury E O is twenty nine inches because the deepness of the pressing water A B E F is thirty four foot And the hight of the VVater N R is thirty four foot because the hight of the Air G H above A B is six thousand fathom or thereabout And for the same reason is the Mercury O P twenty nine inches THEOREM XXVII
Quick-silver therefore the Pillar of Air that counterpoiseth the Pillar of Quick-silver in the Torricellian Experiment is 14000 times higher The one is 29 inches and therefore the other is 406000 inches which will amount to 33833 foot or about 6766 fathom counting five foot to a fathom And because Air is counted 1000 times lighter then Water therefore the Pillar of Air that sustains the Pillar of Water is 1000 times higher The hight of Water by the Pressure of the Air is 34 foot and therefore the hight of the Air is a thousand times 34 foot And because Water is reckoned 14 times lighter than Mercury therefore you will find even by experience that the Pillar of Water that counterpoises the Pillar of Mercury is 14 times higher For if the Mercury be ten inches the Water will be exactly 140. If it be 29 inches the Water will be thirty four foot The reason is evident because if one inch of Mercury be as heavy naturally as 14 inches of Water it follows of necessity that for making of a counterpoise to every inch of Mercury there must be 14 of Water and these in altitude each one above another Hydrostatical EXPERIMENTS For demonstrating the wonderful Weight Force and Pressure of the Water in its own Element EXPERIMENT I. Figure 6. IN explicating the Phenomena of the Hydrostaticks and in collecting speculative or practical conclusions from them I purpose to make choise of the plainest and most easie Experiments especially in the entry that this knowledge that 's not very common and yet very useful may be communicated to the meanest capacities For if at the first any mystical or abstruse Experiments should be proposed with intricate descriptions they would soon discourage and at last hinder the ingenuous Reader from making progress For if a man do not take up distinctly the Experiment it self first he shall never be able to comprehend next the Phenomena nor at last see the inferences of the conclusions Next though some of the trials may seem obvious yet they afford excellent Phenomena by which many profound secrets of Nature are discovered And if that be 't is no matter what kind they be of Then the grand design here is not to multiply bare and naked Experiments for that 's a work to no purpose for it 's like a foundation without a superstructure but the intention is not only to describe such and such things but to build such and such Theorems upon them and to infer such and such conclusions as shall make a stately building and give a man in a short time a full view of this excellent Doctrine For the first Experiment then prepare a Vessel of any quantity as A B C D near half full of Water whose surface is M H. Prepare also two Glass-pipes the one wider the other narrower open at both ends which must be thrust down below the Water first stopping the two upper orifices E and F. This done open the said orifices and you shall see the Water ascend in the wider to G and in the narrower to H. Now the question is What 's the reason why the Water did not ascend the orifices E and F being stopped and why it ascends they being opened To the first part I answer the Water cannot ascend because the imaginary surface of Water L K is equally and uniformly prest for with what weight the outward Water M L and H K press the said surface with the same weight doth the Air within the two Pipes press it To the second part I answer the Water ascends because the same surface the orifices E and F being opened is unequally prest for the outward Water M L and H K press it more then the Air within the Pipes do The difficulty only is why it is equally prest the orifices E and F being stopped and why it is unequally prest the said orifices being once opened To unloose the knot I must shew the reason why the Air within the Pipes press the surface L K with as great a burden as the outward Water press it For understanding this you must know that when the orifice I is thrust down below the Water there ariseth a sort of debate between the lower parts of the Water and the Air within the Pipes the Water striving to be in at I and the Air striving to keep it out but because the Water is the stronger party it enters the orifice I and causeth the Air retire a little up one fourth part or sixth part of an inch above I and no more which is a real compression it suffers For the orifice E being stopped hinders any more compression than what is said in which instant of time the debate ends the Air no more yeelding and the Water no more urging by which means the Air having obtained a degree of Bensil more then ordinary by the Pressure of that little quantity of Water that comes in at I presseth the part of the imaginary surface it rests upon with as great weight as the outward Water presseth the parts it rests upon But when the orifice E is opened the outward water M L and H K press the imaginary surface L K more than the Air within the Pipe can do And the reason is because by opening the orifice above the internal Air that suffered a degree of Bensil more then ordinary presently is freed and consequently becomes of less force and weight which the Water finding that hath a little entered the orifice I instantly ascends to G it being less pressed then the Water without the Pipe Now the reason why it ascends no higher then G is taken from the equal Pressure of the Body that rests upon the surface M G H For assoon as it comes that length all the parts of the horizontal Plain of Water is uniformly prest with the incumbing Air both within the Pipe and without the Pipe The Water in going up cannot halt mid-way between I and G for then there should be an unequal Pressure in Fluids without motion which is impossible for the Water is still stronger then the Air till once it climb up to G. From this Experiment we see first that in Water there is a Pressure and Force because having opened the orifice E which is only causa per accidens of this motion the Water is prest up from I to G. We see secondly that Fluid Bodies can never cease from motion till there be an equal Pressure among the parts which is evident from the ascent of the Water from I to G which cannot halt in any part between I and G because of an unequal Pressure till it once climb up to G. We see thirdly that Fluid Bodies do not sustain or counterpoise one another according to their thickness and breadth but only according to their altitude because there is not here any proportion between the slender Pillar of Water H K within the Pipe and the outward Water that sustains it I mean as to the thickness therefore 't is no
matter whither the Glass Tubs be wider or narrower that are used in counterpoising Fluid bodies one with another And this is the true reason why 't is no matter whither the Tub of the Baroscope be a wide one or a narrow one seing the Air doth not counterpoise the Mercury according to thickness that 's to say neither the thickness of the ambient Air that sustains nor the thickness of the Mercury that is sustained are to be considered but only their altitudes 'T is true the element of Air is fourteen thousand times higher then the Mercurial Cylinder yet there is a certain and true proportion kept between their heights so that if the element of Air should by divine providence become higher or lower the height of the Mercury would alter accordingly EXPERIMENT II. Figure 6. TAke out of the Water the wide Pipe E G I and stopping the orifice I pour in Water above at E till the Tub be compleatly full Having done this thrust down the stopped orifice I to the bottom of the Vessel and there open it then shall you see the Water fall down from E to G and there halt The reason is taken from unequal Pressure for the Tub being full of Water from E to I that part of the imaginary surface upon which the Pillar of Water rests is more burdened than any other part of it namely more then L or K therefore seing one part is more burdened than another the Cylinder of Water that causeth the burden must so far fall down till all the parts be alike prest in which instant of time the motion ceaseth This leads us to a clear discovery of the reason why in the Baroscope the Mercury falls from the top of the Tub of any height alwayes to the twentieth and ninth inch above the stagnant Quick-silver For example fill the Pipe N Q which is sixty inches high with Mercury and opening the orifice Q the Liquor shall fall out and fall down from N till it rest at R which is twenty nine inch above the open orifice Q. The reason is the same namely unequal Pressure seing one part of the imaginary surface of Air X S upon which the Cylinder of Mercury stands is more burthened then the other next adjacent therefore so long and so far must the Mercury subside and fall down till the part Q upon which the Basis of the Pillar rests be no more burthened than the rest of the parts in which instant of time the motion ceaseth and there happeneth an equal ballance between the Silver within the Tub and the Air without If it be said I see a clear reason why the outward Water M L ought to sustain the inward G I but cannot see why the outward Air T Z S and V R X ought to sustain the inward Mercury R X neither do I see a reason why it should halt at R as the Water rests at G. I answer though sense cannot perceive the one as evidently as the other yet the one is as sure as the other For taking up the reason why it halts at R 29 inches above X you must remember from the 25 Theorem that the Pressure of the Air upon Bodies is equivalent to the weight of 34 foot of VVater perpendicularly or 29 inches of Quick-silver The Pillars of Air then T Z S and V R X being as heavy each one of them as two Pillars of Mercury each one of them 29 inches high it follows of necessity that the Mercury within the Tub must be as high as R. 'T is no wonder to see the Silver halt at R provided R X and Z S were two bulks of Mercury environing the Pipe as the outward VVater environs the wider and narrower Pipe Neither ought any to wonder when the Silver falls down and rests at R nothing environing the Pipe but Air seing the Pressure of the Air is equivalent to the weight of 29 inches of Quick-silver This Experiment is easily made take therefore a slender Glass-pipe of any length beyond 30 inches open at both ends but the lower and Q must be drawn so small by a flame of a Lamp that the entry may be no wider than may admit the point of a small needle or the hair of ones head Then stopping the said orifice pour in Mercury above at the orifice N till the Pipe be compleatly full Next close the said orifice with wet Paper and the pulp of your finger and opening the lower orifice you shall find which is very delightful to behold the Mercury spring out like unto a small silver threed and falling down from the top N shall rest at R the motion ceasing at the narrow orifice Q. This shews evidently that there is not need alwayes of stagnant Mercury for trying the Torrieellian Experiment but only when the mouth of the Pipe below is wide for being narrow the silver runs slowly out and consequently subsides slowly above and coming down slowly to R there rests But when the mouth is wide below the silver falls down so quickly that it goes beyond R before it can recover it self which recovery would never be unless there were stagnant Mercury to run up again From what is said we see first that when one part of a surface of Water or Air is more burthened than another the burthened part presently yeelds till it be no more burthened than the other This is clear from the falling down of the Water from E to G which cannot be supported by the part I because more burthened than the rest We see secondly that the element of Air rests upon the surfaces of all bodies with a considerable weight otherwise it could not sustain the Water before it fall down from E to G for if it did not left upon the surface M H with weight the Water could never be suspended seing the application of the finger to the orifice E is only the accidental cause of this sustentation We see thirdly that according to the difference of natural weight between two Fluids so is the proportion of altitudes between two of their Cylinders therefore Air being reckoned 14000 times lighter then Mercury it followes that the Cylinder of Mercury sustained by the Air must be 14000 times lower and shorter than the Cylinder of Air that sustaines it which appears from this experiment to be true seeing by the Pressure of the Air which is thought to be about 7000 fathom high 29 inches of Mercury is supported between R and X. In a word if Air be naturally 14000 times lighter than Mercury which is very probable then must the altitude of it commonly called the Atmosphere be fourteen thousand times nine and twenty inches that is 406000 or of feet 33833. EXPERIMENT III. Figure 6. WHile the outward and inward Water are of the same altitude withdraw the inward Air E G by suction or by any other device you think fit and you will find the Water rise as high as E which I suppose to be 34 foot above
high But assoon as the Tub is reclined there arises ane inequality between the saids two parties the Pondus of the Cylinder becoming now less than before If you say the quantity of the VVater is the same namely 50 inches in the reclined Tub as well as in the Perpendicular I grant the quantity is the same but the weight is become less Now the reason why the same individual VVater is not so heavy as before is this there are 40 ounces of it supported by the sides of the Tub within which were not while the Tub was erected for in this position the whole weight of the Cylinder rests upon the surface but while the Tub is reclined the said surface is eased and freed of 40 ounces of it this 40 resting and leaning upon the sides of the Pipe within The surface then finding the said Cylinder lighter now than before instantly drives it up from R to E 40 inches And likewise when the reclined Pipe is made Perpendicular the Water falls down from I to D because of the inequality that 's between the Pondus of the Pillar and the Potentia of the surface this surface 50 inches deep not being able to support a Pillar 90 inches high for if this were then one part should be more burthened than another which is impossible It is to be observed that by how much the more the Tub is reclined from a Perpendicular towards the horizontal surface A B C by so much the more growes the inequality between the Pondus and the Potentia and that according to a certaine proportion Hence is it that the Tub being reclined from 60 degrees to 50 there arises a greater inequality between the Pondus of the Cylinder and the Potentia of the surface than while it is reclined from 70 to 60 and more yet in moving from 50 to 40 than in moving from 60 to 50 and so downward till it be horizontal in which position the whole Pondus is lost And contrariwise while the Pipe is elevated the Pondus begins to grow and growes more being lifted up from 10 to 20 than from 1 to 10 and yet more in travelling from 20 to 30 than from 10 to 20 and so upwards till it be Perpendicular in which position the Cylinder regaines the whole Pondus and weight it had This proportion is easily known for it s nothing else but the proportion of Versed Sines upon the line F B for according to what measure these unequal divisions become wider and wider from 90 to 1 according to the same proportion does the Pondus of the Cylinder become less and less and contrariwise according to what proportion the said divisions become more and more narrow from 1 to 90 according to the same measure and rate does the Pondus of the Cylinder become greater and greater EXPERIMENT VI. Figure 9. THis Schematism represents a Vessel fall of Water whose first and visible surface is H I K the second which is imaginary is E F G the third A B C D. Besides these three in Water conceive a fourth in the Air above the Water namely L M N. Upon this aërial surface rests the orifice M of the Tub T M open above Upon the surface E F G is standing the mouth F of the Pipe S F. And upon the surface A B C D stands the Pipe R B open at both ends After the orifice B is drowned below the VVater you will find the Liquor rise from B to H. Then close with the pulp of your Finger the mouth R and lift the Pipe so far up till it have the Position of the Pipe S F and you shall see the VVater hing in it between F and O. Lastly bring the said orifice compleatly above the VVater till it have the position of the Tub T M yet shall the VVater still hing in it as M P. The first question is what sustains the VVater I O for the part F I is sustained by the ambient VVater I answer it cannot be the pulp of the Finger closing the orifice S for though by taking away the Finger the VVater O I falls down and by putting to the Finger it is keeped up yet this proves not the pulp of the Finger to be the principal and immediat cause I say then the VVater O I is suspended by the weight of the incumbing Air resting upon the surface H I K. For understanding this consider as I said before 25. Theorem that the Pressure of the Air upon all Bodies is just equivalent to the weight of 34 foot of VVater Hence then is it that if the Air be able to sustain a Pillar of VVater 34 foot high it must be able to sustain the short Pillar O I that exceeds not four foot The second question is whether the part F be equally burthened with the part E or G for it would seem not seing the VVater O I F is but four foot high whilest upon E or G is resting not only more then a foot of VVater to the top H I K but the whole weight of the Atmosphere upon the said top is resting which is equivalent to the burden of 34 foot of VVater I answer there 's more to be considered than that four foot of VVater which in it self is but of small burden therefore to this we must add the weight of the Air between O and S within the Pipe remember that the orifice S is stopped with the pulp of the Finger which in effect will be as heavy as 31 foot of VVater Put the case then F to be one foot below the first surface H I K and the VVater O I to be three foot then ought the Air O S to have the weight of 31 foot because the surface E F G is able to support a Pillar of 35 foot This I prove because the part E de facto sustains 35 foot because the Air above is equivalent to 34 foot of it and there is a foot of VVater between it and the top namely between E and H. The third question is how it comes to pass that the Water still remains in the Pipe after the orifice M is brought above the surface of the Water for there is here no stagnant Water guarding it as guards the orifice F. I answer that the base M of this Pillar of Water P M as really rests upon the horizontal surface of this Air L M N as a Cylinder of Brass or Timber rests upon a plain Marble Table and after the same manner Remember that the orifice T is stopped all this time with the pulp of the Finger If it be said that the part M is more burdened then the part N seing it sustains four foot of Water which the part N supports not and the Air P T within the Pipe also which is of as much Bensil and Pressure as the Air N Y is of For clearing of this difficulty consider that the Pillar P M is shorter now than before for the orifice M coming up from
D some inches of Water falls out as will be found by experience Suppose then that of four foot six inches fall out if this be then the inclosed Air between P and T must be 〈◊〉 inches longer if this be then of necessity the Bensil of it must be proportionably remitted and slackened whence follows by Metaphysical necessity that it cannot burden the Water P M with as much weight as it had and consequently the surface of Air cannot be so much burdened It must then be no more buâ—dened with them both together than it is with the single Pillar of Air Y N. If then the Water P M be three foot and an half the weight of the enclosed Air T P must be exactly the weight of thirty foot of Water and an half From this experiment we see first the Pressure of the Air for by it the Water O I is suspended and by the same pressure is the Water P M suspended We see secondly that in Air there is a power of dilating it self and that this dilatation never happens without a relaxation of the Bensil We see thirdly that one Fluid cannot sustain another unless the Potentia of the one be equal to the Pondus of the other as is clear from the Aërial surface that cannot sustain the whole four foot of Water but suffers six inches of it to fall out that the Pondus of the rest and the Air above it may become equal to its own Potentia We see fourthly that Fluid Bodies have not only a power of pressing downward but of pressing upward likewise as is clear from the Water O I that 's suspended by the Air pressing down the surface of Water H I K. It presseth upward also while it supports the Water P M. This Experiment also answers a case namely whether or not it is alwayes needful to guard the orifice of the Tub of the Baroscope with stagnant Quick-silver I say then it is not alwayes needful provided the orifice be of a narrow diameter for experience tells that while it is such the Mercury will subside and halt at 29 inches above the orifice though no stagnant Mercury be to guard In making this trial the orifice must be no wider than may admit the point of a needle Or suppose it to have the wideness of a Tobacco-pipe yet will the Mercury be suspended though the end be not drowned among stagnant Quicksilver even as the Water P M is kept up without stagnant Water about it For trial of this you must first let the end of the Pipe be put down among stagnant Mercury and after the Cylinder is fallen down to its own proper altitude lift up the Pipe slowly till the orifice come above the surface and you will find provided you do not shake the Pipe the Cylinder to be suspended after the same manner immediatly by the Air as the Water P M is EXPERIMENT VII Figure 10 11. TAke a Vessel of any quantity such as A B C D E and fill it with VVater And a Glass-pipe such as G F D of 15 or 20 inches long of any wideness closs above and open below Before you drown the open end among the VVater hold the Glass before the fire till it be pretty hot and having put it down you will see the VVater begin to creep up till it come to F where it halts The question now is what 's the reason why the VVater creeps up after this manner 10 or 12 inches above the surface A B I answer the heat having rarified the Air within and by this means having expelled much of it and the Air now contracting it self again with cold the VVater ascends being prest up with the weight of the incumbing Air resting upon the surface of Water A B. There is here surely an inequality between a Pondus and a Potentia that must be the cause of this motion I judge then the inequality to consist between the weight of the Air within the Pipe and the surface of Water C D E. To explicate this I must suppose the Pipe to be thrust down cold in this case little or no Water can enter the orifice D. And the reason is because the Pondus of the Air within the Glass is equal to the Potentia of the surface C D E. But when the Pipe is thrust down hot much of the Air having been expelled by the heat and now beginning to be contracted by cold the Pondus of the Air becomes unequal to the Potentia of the surface and therefore this being the stronger party drives up the Air within the Glass till by this ascent the Pondus of the Air G F and the Pondus of the Water F D together become equal to the Potentia of the surface C D E that sustains them For a second trial bring a hot coal near to the side of the Glass between G and F and you will find the Water to creep down from F toward the surface A B and if it continue any space it will drive down the whole Water and thrust it out at D. To explicate this I must suppose that heat by rarifying the Air within the Glass intends and increaseth the Bensil of it and the Bensil being now made stronger there must arise an inequality between the Pondus of the said Air and the Potentia of the surface C D E the Air then being the stronger party causeth the surface to yeeld By comparing this Experiment with the former we see a great difference between the dilatation of Air of its own accord and by constraint For while it is willingly expanded the Bensil begins to grow slack and remiss and loseth by degrees of its strength even as the Spring of a Watch by the motion of the Wheels becomes remiss But when the dilatation is made by heat and the Air compelled to expand and open it self the Bensil becomes the stronger and the Pressure the greater Notwithstanding though the Bensil of this inclosed Air G F may be made stronger by heat to the expulsion of the Water F D yet if this rarefact on continue any time the Bensil becomes dull and slack And the reason is because Air cannot be expanded and opened to any quantity an inch cannot be dilated and opened to an hundred or to a thousand neither can the Bensil of it be intended and increase to any degree v. g. from one to 20 30 or 100. And therefore as the expansion grows the Bensil must at length slacken But if so be the Air were inclosed as in a bladder knit about the neck with a string then the more heat the more Bensil for in this case there is a growth of Pressure without dilatation And sometimes the Bensil may be so intended with the heat that the sides of the bladder will burst asunder From this Experiment we see first a confirmation of the 21 Theorem namely that there may be as much Bensil and Pressure in the smallest quantity of a Fluid as in the greatest as is
We see secondly that this Pressure is according to Arithmetical Progression as 1 2 3 4 5. because in going down the first 14 inches the Mercury rises one inch in going down the second 14 inches it rises two in going down the third 14 inches it rises three and so forward We see thirdly though a VVater were 100 fathom deep yea 1000 yet the Pressure of the Air above is found at the bottom for supposing this Experiment were 100 fathom deep yet would the Air from above have influence upon it to sustain so many inches of the Mercurial Cylinder A Diver then 10 or 15 fathom under the VVater must be burdened with the weight of the Air as well as with the weight of the VVater so must the Fishes though never so deep We see fourthly that the parts of a Fluid cannot cease from motion so long as there is an inequality of weight between the pondus and the potentia This is clear from the falling down of the Mercury from H to G. And assoon as equality of weight happens the motion ends This is clear from the Mercurie's halting at G. Fifthly that in Mercury as well as in Water or Air surfaces may be distinguished and that these surfaces are endowed with a Potentia or power begotten in them by superior and extrinsick weight This is clear from the imaginary surface D C E that 's made powerful to support 58 inches of Mercury in the Tub and that by the weight and Pressure of the Air resting upon A B. Sixthly that as two Fluids differ in specifick and natural weight so they differ in altitude when they counterpoise one another This is clear from the disproportion that 's between the altitude of the Mercury suspended and the height of the Water and Air suspending G F then is 29 inches and the deepness of the Water from K to N is 34 foot because Water is naturally 14 times lighter than Mercury F B is likewise 29 inches and the hight of the Air that rests upon the surface of Water is six or seven thousand fathom high because Air is 14000 times naturally lighter than Mercury Seventhly that Fluid Bodies counterpoise one another not according to their thickness and breadth but only according to their altitude This is evident for though this Tub were never so wide or narrow yet the altitude of the Mercury is unchangeable Hence it is that the thickest Pillar of Water in the Ocean is not able to suspend more Mercury than the slenderest I mean as to altitude And hence it is that the smallest Cylinder of Mercury no thicker than a silk threed is able to counterpoise a Pillar of Water of any thickness whatsoever We may conclude lastly that when a Diver is 20 fathom under the Water he is under as much burden as if he were under 14 or 15 foot of Quick-silver Suppose a man lying on his belly within a large Vessel and 14 or 15 foot of Mercury poured in upon him surely it may be thought that such a burden were insupportable But put the case the Diver were down 40 fathom then must the burden be doubled This follows because if a Pillar of Water 34 foot high with the weight of the Air superadded be as heavy as 58 inches of Mercury then surely a Pillar 20 fathom high or 100 foot must be as heavy as 170 inches which is more than 14 foot EXPERIMENT X. Figure 14. AGainst the former Experiment there occurres some difficulties which must be answered As first if it be the Pressure of the Water that sustains the Mercury in the Tub see the 13. Figure then the weight of the said Mercury ought not to be found while the Tub is poiâ—ed between a mans Fingers But so it is that when a Diver grips the Tub about the middle and raises it a little from the bottom of the Vessel he not only finds the weight of the Tub it self but the weight also of the 58 inches of Mercury that 's within it But this ought not to be if the said Mercury be sustained by the outward Water In a word it ought not to be found because the said Pillar of Mercury as really stands and rests upon the imaginary surface D C E as a Cylinder of Brass or Stone rests upon a plain Table of Timber or Stone If then it be supported by the said surface why ought I to find the weight of it when I lift up the Pipe a little from the bottom of the Vessel For clearing this difficulty consider that when the Mercury falls down from H to G it leaves a soâ—â— of vacâ—ity behind it wherein there is neither Air nor Water Consider secondly that for this cause there happens an unequal Pressure the top of the Tub without being burdened with the Pillar of Water I H which actually presseth it down and nothing within between G and H that may counterballance that downward Pressure These things being considered I answer to the difficulty and say it is not the weight of the suspended Mercury that I find but the weight of the Pillar of Water I H that rests upon the top of the Tub. If it be said the Pressure of a Fluid is insensible and cannot be found I answer it 's true when the Pressure is equal and uniform but not when the Pressure is unequal as here If it be asked how comes it to pass that the Pillar of Water I H is exactly the weight of the 58 inches of Mercury I answer besides the said Pillar there is another of Air that rests upon the top of it which two together are exactly the weight of the suspended Mercury I H being of the same weight with the Mercury G F and the foresaid Pillar of Air being of the same weight with the Mercury F B. To make it more evident remember that one inch of Mercury is exactly the weight of 14 inches of Water and that one inch of Mercury is of the same weight with 14000 inches of Air. If this be then must the Pillar of VVater I H that 's 34 foot high and of the same thickness with the 29 inches of Mercury G F be of the same weight with it seing 29 inches are to be found 14 times in 34 foot For the same reason is the Pillar of Air namely S I that rests upon the top of the Pillar of VVater I H of the same weight with the 29 inches of Mercury F B. For after a just reckoning you will find that 29 inches will be found 14000 times in the Pillar of Air that rests upon the Pillar I H. Or in a word the hight of the Air is 14000 times 29 inches But here occurrs another difficulty Let us suppose there were a Tub six foot high one inch wide having the sides 3 inches thick Imagine likewise the said Tub to be under the water 34 foot with 58 inches of Mercury in it as is represented in this 14 Figure This being supposed the Pillar of Water E A F
touch the ground being detained by the way by a surface counterpoising it Or if it did touch through the swiftness of the motion it would surely as it were â—rebound and be carried up again It is alwayes to be remembred that in such trials the Air is supposed not to follow or to be united after the Stone passeth thorow Now if the Air be able to do this far more the VVater that 's a body a thousand times heavier We see fifthly the reason why heavy bodies move so easily thorow Air and Water namely because the parts that were divided by the body that is moved are presently reunited and closed again by which means it is driven forward the Pressure upon the back being as much as the Pressure before If this were not no body whatsoever would be able to move it self one foot forward For example if when a man hath advanced one step forward the Air did not close again upon his back the force of the Air upon his belly and breast would not only stop him but violently thrust him backward We see sixthly the reason why the same body descends with more difficulty thorow Water than Air because a surface of Water is far stronger than a surface of Air. We see seventhly that a heavy body is never suspended by a surface of Water or Air in going down till once it hath displaced as much Water or Air as will counterpoise it self in a ballance This is clear from the Brass C D that goes alwayes down till it expell its own weight of Water For this cause if a Mill-stone were demitted or sent down from the top of the Air and never rested till it came within 40 fathom of the Earth then so much Air as is expelled by the descent is the just weight of the stone We see eighthly the heavier a body be naturally than Water it goes the further down and the lighter it is it sinks the less For if C D were of Gold it would go further down than being of Brass or Iron and if C D were a stone that 's lighter in specie than Brass it would not go so far down This lets us know the reason why thicker blacker and heavier clouds comes nearer to the Earth than thinner whiter and lighter VVe see ninthly that the Pressure of the Air is determinable even in its heighest degree and seemes to be the same in all places of the world but the Pressure of the Water is not so The reason of the first part is because the Element of Air seems to be of the same hight in all places and therefore we may know its outmost Pressure which is just equivalent to the weight of 28 or 29 inches of Gold or Mercury But because the deepness of the Sea is variable therefore the Pressure is variable likewise Yet if the exact deepness of the deepest place were known it were as easie to determine the greatest Pressure of it as to determine the greatest Pressure of the Air. We see tenthly that a very small weight added or subtracted in height will change and alter the counterpoise of a Fluid Because if you lay but one ounce upon the top of the brass at F it presently subsides accordingly or take one ounce from it and it rises But though never so much weight be added to it or subtracted from it in thickness no alteration follows Therefore though this piece of Brass C D that 's now but 12 inches in thickness were made 24 by which means the weight would be tripled and more yet the same surface A N B would sustain it yet add to it in altitude but one inch and presently it sinks down proportionably This evidently discovers the reason why it s as easie for the Air to support a Cylinder of Mercury 3 inches thick as to support a Cylinder half an inch thick and why it cannot support more in height than 29 inches and why it cannot support less Now the reason why a thicker Pillar is as â—asily suspended as a thinner is this because if a Pillar of Mercury be thicker and consequently heavier than it takes a broader and consequently a stronger surface of Air to rest upon if it be but slender and so but light then it takes a lesser part of a surface to bear it up and consequently a weaker by which means the Pondus of the one is alwayes proportionable to the Potentia of the other Is it not as easie for a Pillar of stone 6 foot in Diameter to support another six foot in Diameter as it is for a Pillar one foot in Diameter to support a Pillar one foot in Diameter But as a Pillar one foot in Diameter cannot support a Pillar 6 foot in Diameter neither can a surface of Air one inch in Diameter support a Pillar of Mercury 6 inches in Diameter But why should a larger part of a surface be stronger than a narrower part I answer the one is stronger than the other for that same reason why a thicker Cylinder is heavier than a thinner for what I call strength in a surface it s nothing else but weight and what I call weight in a Cylinder it s nothing else but strength The same thing hath two names because the pillar of a Fluid presseth down and the surface supports therefore in the one it s called pondus in the other potentia As when two scales are in equilibrio either this or that may be called the pondus or either this or that may be called the potentia Now I say if a part of a surface four inches broad have as much weight or force in it as a Pillar of Mercury four inches thick then surely a part of a surface eight inches broad must have as much weight and force in it as a Pillar of Mercury eight inches thick But why ought a surface to succumb when the Pillar grows in hight and not to fail when it grows only in breadth Ans. VVhen it grows in breadth the pondus never exceeds the potentia but when it becomes higher then it becomes heavier That 's to say when a Pillar grows broader there 's not one part of â—he surface that sustains it more burdened than another seing the part eight inches broad is no more prest with a Pillar eight inches thick than the part four inches broad is prest with a Pillar four inches thick as eight ounce of Lead in this Scale is no more counterpoised with eight ounce in the other Scale than four ounce in this Scale is counterpoised with four in the other But when a Cylinder grows in hight the pondus exceeds the potentia one part of a surface being more burdened than another We see eleventhly that in a large surface of a Fluid wherein are many parts each part is able to sustain its own proper burden So a part eight inches in Diameter supports a Pillar eight inches thick and a part four inches supports a Cylinder four inches thick but cannot support a Pillar
fasten it to the bottom of the other Glass at L. Next for sinking the two Glasses take two weights of Lead and fasten the one to the bottom at M and the other to the open part of the Glass at S and T. The two weights then are P and Q each one of them about 10 or 12 pound weight These things being done let first down the Glass G M till the weight Q sink it five fathom namely from A to B and if you pull it up you will find the bottom covered with Water from M to I about four or five inches Let it down next from A to C ten fathom and you will find more Water in it even as much as fills it from M to 2 about seven or eight inches In passing from C D the Water rises from 2 to 3. If you sink it from D to E the VVater rises from 3 to 4. The VVater rises from 4 to 5 when the glass is come the length of F. And lastly when the Glass is at G the lowest fathom the VVater is as high as K. Let down next the other Glass from A to B and you will find the Water rise in it from H to I four or five inches as in the other Glass In going down from B to C it rises from 1 to 2. From C to D it rises from 2 to 3. From D to E it rises from 3 to 4 and so forward till the Glass come to the lowest fathom where the Water rises as high as I. There are here several Phenomena to be considered First that the Water creeps in at the orifice G and fills the under part of the Glass from M to K. Secondly that not one particle of Air comes out all the time the VVater is in going in Thirdly that this Air is comprest from M to K nine inches Lastly that the ingress of the Water is according to unequal proportion because while the Glass passeth from A to B more VVater creeps in at G and fills the bottom then in passing from B to C. And more in going down from B to G than in going down from C to D as is clear from the unequal divisions 1 2 3 4 5 6 For understanding the reason of the first remember that in this deep Water there is a Pressure and that this Pressure grows as the VVater grows in deepness It is then by vertue of this that the VVater creeps in and fills the bottom of the Vessel for in effect every part being under a burden and being therefore desirous to liberat themselves from it they take occasion to thrust in themselves finding as it were more ease here than without the Air within the Glass being under less Pressure than the VVater without The second Phenomenon is caused by the straitness and narrowness of the hole G for this entry being no wider than the thickness of a Sack-Needle the Air cannot go out while the VVater is coming in that is the passage is so strait that the one cannot go by the other This leads us to the reason of the third for if not one particle of Air go out all the while the Glass is in going down then surely the VVater filling between M and K must compress the Air and reduce it from twelve inches to three But the greater difficulty is why the ingress of the VVater is according to unequal proportion For understanding this consider that this inequality is not caused by any unequal Pressure that 's in the VVater for if this were true then there ought to be less Pressure in the surface F than in the surface E and less in E than in D which is false and absurd This inequality then must flow from the nature of the Air it self that naturally suffers compression after such a manner 'T is evident from the compression of Air in Wind-guns for less force is required to compress the first span than to compress the second or contrariwise more strength is required to compress the third span than the second more to compress the fourth than the third and so forth 'T is evident in all bodies endowed with Bensil as in the Spring of a Watch that requires more strength to bend it in the end than in the beginning For a second trial pull up from the bottom of the Water the Glass L I H and when it comes above you will find nothing in it The reason is because the Vessel being open between T and S the whole VVater I H falls down by degrees but in effect is really thrust out by the strong Bensil of the comprest Air I L that now expands it self when it finds the Glass go up thorow the VVater whose Pressure is less and less from the bottom to the top but the contrary effect follows when the other Glass is pulled up namely the VVater remains within the Glass and the Air above it is thrust out by degrees as the Glass comes nearer to the top For understanding the reason of this consider first that while the orifice G is level with the lowest surface where it now is that 's supposed to be 30 fathom deep there is a real counterpoise between the inclosed Air G K and the ambient VVater without for with what force the one strives to be in with the same force the other endeavours to be out and because they are in equal terms therefore the one cannot yeeld to the other If you please to give the victory to the VVater then let the Glass go further down but if you desire the Air to overcome then must the Glass be pulled up Pull it then up from the place it is in till it come to F and you will find a considerable quantity of Air come out at G and after 2 or 3 minuts of time emerge and come to the top A in form of round Bells or Bubbles The deepness and groseness of the Water thorow which the Bubbles come makes their motion so slow The reason of this eruption must be less Pressure of Water in the surface F than in the lowest G from whence the Glass came Suppose then the lowest to have six degrees of Pressure F to have five E to have four D three C two and B to have one and supposing the inclosed Air K G to be equal in force to the Pressure of the lowest fathom it must then have six degrees of Bensil in it Put the case then that with six degrees of Bensil it come to the surface F that hath but five it must surely break forth and overcome the force and power of that surface for 't is impossible that two Fluids can be unequal in force and power but the strongest must overcome and the weakest yeeld therefore when the orifice comes to F the Air being stronger than the Water breaks forth and as long doth this eruption continue as inequality of power continues between the one and the other In pulling up the Glass from F to E other five fathom more
a piece of Lead or stone in an Artificial Ballance for knowing how many ounces or pounds it is of as if a man should endeavour to weigh the Water E F R by help of the Ballance above which in effect is impossible EXPERIMENT XVIII Figure 25. MAke a Wooden Ark after this following manner The Planks must be of Oak an inch thick The height 40 inches The breadth 36. Closs on all sides and above and open below And because the form is four-square there must be four Standarts of Timber in each corner one to which the Planks must be nailed Four likewise upon the top crossing the other four at right angles to which the cover must be joyned The sides must be plained and the edges both plained and gripped in all the parts that the joynings may be closs Upon the top fasten a strong Iron Ring as at N through which must be fastned a Rope of so many foot or fathom And because the use of this Engine is for Diving under the Water it must therefore be all covered over with Pitch within and without especially in the couplings And because this Instrument cannot sink of its own accord it must have a great weight of Lead appended to it for that cause whereupon the Divers feet must stand while he is in going down The precise quantity and weight of it cannot be determined because it depends upon the quantity of the Ark which if large requires a great weight if of a lesser size requires a lesser weight But whatever the dimensions of the Ark may be the weight of the Leaden-foot-stool can easily be found out by trial This Invention then is for Diving a most excellent Art for lifting up of Guns Ships or any other things that are drowned below the Water And it is in imitation of the Diving bell already found out and made use of with success It is called a Bell because of the form that represents a Church-bell indeed being round wide below and narrower in the top only the matter is of Lead It seems it is of this mettal first because Lead is weighty and will therefore easily sink secondly because it 's easily founded and will by this means being of one piece be free of rifts and leaks thirdly it being of Lead will be of a considerable strength for resisting the force of the VVater that ordinarily breaks in pieces Vessels that are weak I cannot well divine and guess the reason why first it is round and next narrower above than below unless because its more easily founded after this way than after another This device here described is named a Diving Ark first because it is of Timber and next because it saves a man from being overwhelmed with the Waters I prescribe it of Wood because of less trouble and expence in making of it 'T is four square because it contains under this Figure far more Air than if it were round even as much more as a square Vessel 30 inches wide contains more than a round Vessel 30 inches wide Now the more Air that 's in the Vessel the easier is the respiration and the longer time is the man able to abide under the VVater which two things are of great advantage to this Art For if by a guess we reckon how much more Air is in the one than in the other we will find in the Ark as before it is described 30 square foot of Air but in the Bell though it be 36 inches wide as well above as below yet little more than 23 will be found which is a considerable difference But far less must be in it seing it's narrower above than below Besides this advantage there are others very useful for being of Wood it 's more tractable Next several Knags of Iron may be fastened conveniently to the sides within to which a man fastning his hands may keep his body fixed and sure in going down and coming up Moreover if a man were in hazard to be confounded with fear or lose the right exercise of his senses and so be in danger of falling out of the Ark or if his feet should slide off the foot-stool and his hands fail him too a chord knit to one of those and fastened about his wast or middle might bring him up though he were dead Then it s far easier to cut out a window or two in the sides of it not very large but little as K and I whereby they being covered with Glass a man may see at a distance what 's upon the right hand and what 's upon the left and what is before This device is of excellent use for through the want of it the Diver sees no more but what is just below him which sometimes when he is near the ground will not exceed the compass of a large Milâ—wheel But if so be three holes be cut thorow one on every hand and one before he may see as much bounds and all things in it as if he were not inclosed and invironed with a cover A little schelf likewise may be fixed upon the one side or the other for holding a Compass with a Magnetical Needle for knowing how such and such a thing lies in the ground of the Sea In one of the corners may hing a little bottle with some excellent spirits for refreshing the stomach under VVater Many moe advantages I might name this Engine being of Timber but shall forbear leaving the collection of them to the ingenious Reader and proceeds to answer some objections that may be made against it First if this Engine be made of Wood it will not sink so easily as being made of Lead I answer this difficulty is soon overcome namely by making the Foot-stool the heavier therefore how light soever it be a weight may be found to counterpoise it in the VVater If it be judged too light in Timber it may be lined with Lead especially without Secondly if it be of VVood there must be couplings and joynings in it and so rifts and leaks in it through which the VVater may come I answer there is less difficulty here than in the former because the joynts may be made so closs in all the parts and may be so covered over with pitch or with some such like matter that it may defie either Water to come in or Air to go out Thirdly if it be made of VVood it will be in hazard of breaking by the force of the VVater for oft times its found that the strongest Hogshead will burst asunder by the Pressure of it if they go but down 7 or 8 fathom I answer this objection flows from the ignorance of the nature of Fluid bodies If so be then that a man knew that the Pressure of VVater is uniform most equal and presseth upon all the parts of a body within it alike no such scruple would occurre I say then the Ark though no thicker in the sides than a thin sawen dale will go down in spight of all the
same bladder and blow it stiff with Wind and knit the neck as afore And you will find that in the up-coming the sides of it will burst asunder with a noise When the Bladder is thus full of Wind 't is supposed that there is a sort of counterpoise between it and the Air of the Ark. But as the Ark ascends the Air of it becomes weaker and weaker while in the mean time the Air of the Bladder suffers no relaxation therefore when the Ark comes near the surface there arises a great disproportion between the one Air and the other as to strength and therefore the Air of the Bladder being the strongest rents the sides in pieces and comes out with a noise Or blow it but half full of wind and you will find before the Ark come near to the top the said Bladder to be bended to the full For a third trial take a Glass such as they use in Caves for preserving of Brandy and stopping the mouth closely take it down with you in the Ark and you will see the sides of it break in pieces before you go down four or five fathom The strong Bensil of the ambient Air is the cause of this If you take it down with the orifice open no hurt shall befal it Or if you stop the orifice in the up-coming you will find the same hurt come to it But here is the difference in the first bursting the sides are prest inward by the ambient Air in the second the sides are prest outward by the Air within the Glass For a fourth trial take a round Glass-bottle pretty strong in the sides and when it is down with you in the Ark 14 or 15 fathom stop the mouth of it exactly and when it comes above you will find a considerable quantity of Wind come out of it when the orifice is opened This evidently demonstrats that the Air within the Ark 12 13 or 14 fathom down is under a far stronger Bensil then the Air above For a fifth trial let a man apply to his skin a cold Cupping-Glass when he enters the Ark and he will find such a swelling arise within it as when it is applied hot by a Chyrurgion This tumor begins to rise assoon as the Ark begins to go down The reason is evident from unequal Pressure the parts within the Glass being less prest than the parts without For a sixth trial take a common Weather-Glass and Place it in the Ark and in the going down you will see the liquor creep up in it by degrees as the Ark goes down as if some extraordinary cold were the cause of it And as the Ark comes up by degrees the said liquor creeps down by degrees The cause of this Phenomenon is not cold as some might judge but the strong Bensil of the Air within the Ark that so presseth upon the surface of the stagnant Water that it drives it up If you take with you a Weather-Glass hermetically sealled no such thing will follow because the outward Pressure is keeped off 'T is not then cold that 's the cause but weight By the way take notice that all common Weather-Glases are fallacious and deceitful because the motion of the Water in them is not only caused by heat but by the weight of the Air which sometimes is more and sometimes less as frequently I have observed and as hath been observed by others This difference is found by the alteration of the altitude of the Mercurial cylinder in the Baroscope which is more and less as the Pressure of the Air changeth In fair weather and before it comes the Mercury creeps up In foul and rainy weather and a pretty while before it fall out it creeps down Because in fair weather the weight of the Air is more than in rainy and dirty weather December 13. 1669. I found the altitude 29 inches and nine ten parts of an inch at this time the heavens were covered with dry and thick clouds and no rain followed March 26. 1670. I found the altitude no more than 27 inches and nine ten parts at which time there was a strong Wind with rain Between these two termes of altitude I have found the Mercury move near a twelve moneth 'T is a most sure prognosticator for if after rain you find the Mercury creep up in the morning you may be sure all the day following will be fair notwithstanding that the heavens threateneth otherwayes If after fair weather the Mercury subside and fall down a little you may be sure of rain within a short time though no appearance be in the present It falls down likewise when winds do blow What the true cause is why there is such an alteration in the Pressure of the Air before foul weather and fair and in the time of it it is not easie to determine But we proceed Trial likewise might be made by fiting a great piece of Ordnance above whether the report would be heard below the Water or not This would determine the question whether Water be a fit medium for conveying sound as Air is Item whether or not the Sea water be fresher at the bottom than near the top which is affirmed by some Item whether sounds be as distinct in such a small portion of Air as they are above This might be tried with a Bell of a Watch. If need were a little chamber Bell might be hung within the Ark and a small chord might pass up from it through the cover whereby the persons above might by so many tingles speak such and such words to the Diver I have demonstrated before that though there were a little narrow hole made in the cover above yet neither Air would go out nor Water come in If a man were curious he might have a window not only in the sides but in the roof above covered with a piece of pure thin Glass thorow which he might look up after he is down two or three fathom and see whether there appeared any alteration in the dimensions of the body of Sun or not or seemed nearer EXPERIMENT XIX Figure 26. THis Figure represents a deep Water whose first and visible surface is F G. The imaginary surface is E L C 34 foot below it A D B is a Siphon working below this VVater with Mercury A E L is a Vessel with stagnant Mercury among which the orifice A is drowned the other orifice B existing among the Water D M is the hight of the Siphon above the line of level which I suppose is 58 inches For making it work stop the two orifices closely and pour in as much Mercury at a hole made at D as will fill both the legs Then stopping the said hole open the two orifices A and B and you will find the liquor run as long out at B as there is any almost in the vessel A E L. For evincing this which is the only difficulty consider that if this Siphon were filled with Water and made to work only
with Air as is clear from daily experience the liquor would run out constantly at B. Because there is here an unequal Pressure the surface of Air N B being more burdened than the surface E L C but where unequal Pressure is in Fluids according to the 12th Theorem motion must follow I prove the surface N B to be more burdened than the surface E L C because the Water B D is heavier than the Water L D as is evident to the eye The Air B therefore sustaining far more weight than the Air E L must cede and yeeld Next there is here a pondus and a potentia the pondus is the VVater L D the potentia by which it is counterpoised is the Water B D but these are unequal B D being heavier than L D therefore according to the 33 Theorem these two Fluids cannot cease from motion If it be said that the surface N B is stronger than the surface E L C seing it is lower I answer the difference is so unsensible that they may be judged but one Now I say if this Siphon work in Air with Water it must likewise work in Water with Mercury Therefore this Siphon being 34 foot below the first surface F G the liquor must run out constantly at B. Because there is here an unequal Pressure the surface of VVater N B beâ—ng more burdened than the surface E L C. Though there be more weight in N B than in E L C because it is lower yet because the difference is not so much as is between the weight of B D and the weight of L D it proves nothing Note here that so long as D is within 58 inches of E L C this Siphon will work The reason is because the Pressure of 34 foot of VVater with the Pressure of the Air upon F G are able to raise Mercury exactly 58 inches But if D exceed that hight no Art will make the liquor run out at B. Note secondly that this Siphon will operate with Air and VVater though the top D were 34 foot above M and the reason is because the Pressure of the Air is able to raise a pillar of Water to that hight Note thirdly that if there were an orifice opened at C upon the level line E L C the two Waters would become of the same weight the one not being able to move the other If you bore a hole at R the liquor ascends from R to D and goeth down from D to A and so the motion ends But if the leg A D were six times wider than B D the liquor would not run out at B. I shall answer this in the close From this Experiment we see first that the motion of Fluid Bodies up thorow Pumps and Siphons is not for shuning vacuity but because they are prest up violently We see next that when the Pressure is uniform there is no motion in Fluids but assoon as one part is more prest than another motion begins because this Siphon will not operate if the orifice be made in C but if so be it be in D then the motion begins because there is here an unequal Pressure which was not in the other We see thirdly that Fluids have a determinate Sphere of activity to which they are able to press and no further because this Water is not able to press Mercury higher than 58 inches So the Air cannot raise Water higher than 34 foot If this Water were 68 foot deep the Sphere of it's activity would be 116 inches We see fourthly that in Fluids there is a Pondus and a Potentia and that the inequality of weight between the two is the only cause of motion We see fifthly that as long as this inequality of weight continues as long continues the motion because as long as B D is heavier than L D the motion perseveres We see sixthly the possibility of a perpetual motion in Fluids because the liquor runs perpetually out at B. If it be said the motion ends when the stagnant Mercury A E L faileth I answer this stop is only accidental and not essentially from the nature of Fluids If it be enquired whether or not would the Mercury run out at B upon supposition the shank L D were twice as wide as the shank B D I answer it would If it be said that the one is far heavier than the other namely L D than D B. I answer weight in Fluids is not counted according to thickness but according to altitude EXPERIMENT XX. Figure 27. THis last is for demonstrating the precise and just weight of any Pillar of Air Water Mercury or of any other Fluid body if some of their dimensions be but once knowen A B then is a square Pipe 12 foot high and six inches in wideness full of Water resting upon the surface of Air A C. And E G is a square Pipe 12 foot high and 12 inches wide full of VVater resting upon the surface of Air E F. None needs to doubt but the two Waters will be suspended after this manner even though the orifices A and E were downward especially if they be guarded with Water but the demonstrations will be the more evident that wee suppose the two Pillars of Water to be suspended as they are From this Experiment I say first that the Pillar of Air C D is 168 pound weight at least which I prove thus The VVater A B is 168 pound therefore the Air C D must be as much I prove the Antecedent because it 's a Pillar of VVater 12 foot high and six inches thick but every half cubical foot of VVater that containes 216 inches weighs seven pound therefore seing the Pillar is 12 foot it must contain 24 half feet but 24 times 7 is 168. The only difficulty is to prove the Connexion which I do thus from the seventh Theor. all the parts of a Fluid in the same Horizontal line are equally prest but so it is that the part A and the part C are in the same horizontal surface therefore the part A and the part C are equally prest But if the part A and the part C be equally prest the Pillar of Air C D must be as heavy as the Pillar of VVater A B. I say secondly that the Pillar of Air F H weighs 672 pound I prove it thus The Water E G weighs 672 pound therefore the Air F H weighs as much The Antecedent is clear because E G is a square Pillar of VVater 12 foot high and 12 inches thick but every cubical foot of VVater weighs 56 pound but 12 times 56 is 672. I prove the connexion as before All the parts of an horizontal surface are equally prest therefore the part F must sustain as much burden as the part E. To proceed a little further let us suppose the Pipe A B to be 34 foot high and the Pipe E G to be as much I assert then thirdly the Pillar of Air C D to weigh 476 pound which I prove
as before All the parts of the same surface are burdened with the like weight but the part A sustains 476 pound therefore the part C must support as much The Connexion is evident and the Antecedent is so too because the VVater A B being 34 foot high and six inches thick must weigh 476 pound for if 216 inches weigh seven pound 14688 inches must weigh 476 pound I assert fourthly the Pillar of Air F H to weigh 1904 pound which I demonstrat by the former Medium All the parts of a Fluid that ly in the same horizontal surface are equally prest but so it is that E and F do so ly therefore F must be as much burdened as E the Water therefore E G weighing 1904 pound the Air F H must weigh as much For if 216 inches of Water weigh seven pound 58752 inches for so many are in the Water E G must weigh 1904 pound Let us suppose secondly the Tub A B to be only 29 inches high and the Tub E G of the same hight and that six inches wide and this 12 inches wide I affirm then fifthly the Air C D to weigh yet 476 pound and the Air F H to weigh 1904 pound Because the Pillar of Mercury A B weighs 476 pound and the Pillar of Mercury E G weighs 1904 pound therefore if A B be 476 C D must be as much And if E G be 1904 F H must be of the same weight I prove the Mercury A B to weigh about 476 pound though it be but 29 inches high because it is 14 times heavier than Water For the same cause doth the Mercury E G weigh about 1904 pound I say about because 34 foot containes 29 inches more than 14 times Let it be supposed thirdly the Pipe E G being 34 foot high to have the one half of it I G full of Air and the other half E K full of VVater I affirm then sixthly the part E and the part F to be yet equally burdened That 's to say the VVater E K that 's now but 17 foot makes as great a Pressure upon E as when it was 34 foot The reason of this is surely the Pressure of the Air I G that bears down the Water K E with the weight of 952 pound the half of 1904 pound If it be said according to the Theorem 21 that there is as much Pressure and weight in the least part of a Fluid as in the whole therefore the Air I G must be as heavy as E H. I answer I G is not so heavy as F H because the Water E K impending in the lower part of the Tub hath occasioned the Air I G to expand it self so many inches by which means it loseth so many degrees of it's Bensil If you remove the Water E K then will the Air I G be as heavy as F H because E K being Air it reduceth I G to that same degree of Bensil with it self but when the Air E is burdened with the Water E K it cannot make the Air I G of that same weight with it self Let us suppose fourthly that only eight foot and an half of Water are in the Tub namely between E and N. I say then seventhly that the part E is as much burdened with it as when the Pipe was full because the 25 foot and an half of Air N G is exactly as heavy as the 25 foot and an half of the Water that 's gone I prove it thus The Air E hath the weight of 1904 pound in it self seing the weight of the surface is alwayes equal to the weight of the Pillar but being burdened with the VVater E N that weighs 476 pound it cannot press up with more weight then with 1428 pound and therefore the top of the Water N must press upon the under part of the Air that 's contiguous with it with 1428. If this be the Air N G must press down with as much seing according to the 20 Theorem it is impossible that one part of a Fluid can be under Pressure unless the next adjacent part be under the same degree of Pressure Therefore I conclude that the 25 foot and an half of Air N G is as heavy as the 25 foot and an half of the Water that 's gone This makes it evident also that when the Pipe is half full of VVater as E K the Air I G hath the weight of 952 pound Because E being in it self 1904 but being burdened with E K 952 it cannot make the top of the Water K press upon I with more weight than 952 and therefore by the 20 Theorem the Air G I must weigh 952 likewise I affirm eighthly that when the Pipe is full of Water from E to G if a man poise it in his hand he doth not find the weight of the Water E G. And the reason is because it 's sustained by the part of the surface E. But if the Air E sustain it my hand cannot sustain it I find then only the weight of the Tub but not the weight of the VVater within it I say ninthly that when I poise the said Tub I find the whole weight of the Pillar of Air L M which is exactly 1904 pound I prove it thus The pondus of a Fluid is then only found when there is not a potentia to counterpoise it or at least when the potentia is inferior to the pondus but there is here no potentia counterpoising the pondus of the Air L M. Therefore I must find the weight of it when I lift up the Tub. The major proposition is clear from the tenth Theorem It 's evident also from common experience for while a ballance is hanging upon a nail with six pound in the one scale and nothing in the other you will find the whole burden if you press up that one scale with the palm of your hand But if so be there were six pound in the opposite scale you will not find the first six and the reason is because it is in equilibrio with other six 'T is just so here I must find the weight of the Air L M while I poise the Tub because it wants a weight to counterballance it I prove the minor proposition thus If any thing counterballance the Air L M it must either be the Air below namely the part E or the Water E G but neither of the twain can do it Not the Air E because it hath as great a burden upon it as it is able to support namely the Water E G that weighs 1904 pound And for this cause not the VVater it self seing all the force it can have to counterballance L M is from the surface of Air E but this is in equilibrio with it already I said that the Air L M was exactly 1904 pound weight This also is evident because it is just of these same dimensions with the Air F H. If it be said the Air L M must be thicker seing it's equal to
a magnitude of Water 34 foot in hight 12 inches in length and six inches in breadth Though the weight of any Pillar of Air may be known by knowing only the dimensions of it in breadth and length yet the weight of a Pillar of Water cannot be known unless all the three common dimensions of it be first known The reason is this the Pillars of Air are all of the same hight but the Pillars of Water in the Ocean are of different hights therefore not only must they be known secundum longitudinem latitudinem in length and breadth but secundum profunditatem that is according to deepness 'T is easie to know then what each particular Pillar weighs First then try how much weight is in a cubical foot of Water and having found this to be v. g. 56 pound you may determine that a Pillar of Water 34 foot high and 12 inches thick weighs 1904 pound A Pillar 34 foot high and six inches thick weighs 476 pound Note that in a Cube of Water six inches thick there are 216 inches which weighs seven pound In a Pillar 12 inches thick and 20 fathom or 100 foot high you will find 5600 pound weight In one of the same thickness but 200 fathom high there are 56000 fifty six thousand pound weight In a Pillar three foot square and 20 fathom deep there are 50400 fifty thousand and four hundred pound weight Make it 800 fathom high with that thickness and it will weigh 504000 five hundred and four thousand pound But if according to the Theorem 25 you consider the weight of the Air above it will weigh 521136 five hundred twenty and one thousand one hundred thirty and six pound A Pillar 12 foot square and 300 fathom deep weighs 12096000 twelve million ninety and six thousand pound Lastly suppose there were a bulk of Water 500 fathom deep and 500 fathom thick such a magnitude would weigh 8750000000 eight thousand seven hundred and fifty million of pounds But if the Pressure of the Air that rests upon a surface of Water 500 fathom in breadth and length be taken in that weighs 119000000 a hundred and nineteen million of pounds the total that the bottom of the sea sustains must be 8940000000 eight thousand nine hundred and fourty million of pounds or 558750000 five hundred fifty and eight million seven hundred and fifty thousand stone weight I infer from the fifth assertion that the lightest of Fluids may be brought to an equilibrium with the heaviest For though Mercury be 14000 times heavier than Air yet the part of the surface A is no more prest with the Mercury A B then the part C is prest with the Air C D. Secondly that 29 inches of Mercury are of the same weight with 34 foot of Water Thirdly the heavier a Fluid be naturally it hath the less altitude in the Natural Ballance and contrariwise the lighter it be it hath the more altitude This is clear from the Mercury that 's 29 inches the Water that 's 34 foot and the Air that 's counted 6867 fathom I infer from the sixth assertion that two Fluids of different gravities may make an equilibrium with a third of the same kind Because the 27 foot of Air I G and the 17 foot of Water E K are in equilibrio with the Air F H. I infer secondly that 17 foot of Air may be as heavy as 17 foot of Water because the Air I G is exactly as heavy as the Water E K. I infer thirdly that the Bensil of a Fluid is a thing really distinct from the Natural weight of it because the Pressure of the Air I G is 952 pound but the natural weight of it will not exceed if it were weighed in a Ballance two or three ounces I infer fourthly that Air cannot suffer dilatation but it must lose of it's Pressure Because the Air I G that ought to weigh 1904 pound weighs only 952. For understanding this you must know that when a Pipe is about half full of Air and half full of Water and inverted so much of the Water falls out and consequently so many inches doth the Air above it expand it self So to make this Pipe that 's 34 foot high half full of Air and half full of Water you must pour in about 19 foot of Water and the 15 foot of Air that 's in it besides will when the Pipe is inverted go up and expand it self to 17 foot two foot of Water falling out I infer from the seventh assertion that when there are two Fluids of different gravities and weights counterpoising a third by what proportion the one grows lighter by that same proportion the other becomes heavier For when the VVater E K that weighs 952 pound becomes E N that weighs 476 the Air above it that weighed 952 becomes now 1428 pound I infer from the eighth that the pondus of a Fluid cannot be counterpoised by two distinct powers Because the 34 foot of Water E G cannot be both sustained by the part of the surface of Air E and my hand I infer from the ninth that the Pressure and weight of a Fluid may be found even in its own Element by sense Because in poising of the Tub I find the weight of the Air L M. I infer secondly that the weight of a Fluid is only found in its own Element when there is not a potentia to counterpoise the pondus of it because I find only the weight of the Air L M because it wants a potentia to counterpoise it I infer thirdly that it is very possible even in the Artificial Ballance to weigh a Fluid in its own Element and to know the precise weight of it to a grain For this cause take a small chord and fasten therewith the top of the Pipe G to the Scale of a Ballance and the Lead or Stone that makes the counterpoise in the opposite Scale is the just weight of the Air L M. To put a close to this Experiment let us suppose the Pipe E G to be 68 foot high and void of Air. If then the orifice E be drowned among stagnant Water the Liquor of its own accord as it were will rise from E to K 34 foot the other half I G remaining empty This evidently shews that the Pressure of the Air hath a Sphere of Activity beyond which it is not able to raise or press up a pillar of VVater 'T is folly then to think that Water may be conveyed over high places by the help of a Siphon v. g. from the one side of a Hill over the top to the other side For if that hight exceed perpendicularly 34 foot no Art will do it Yet contrariwise it is possible to transport Water by Pipes and Siphons not only 34 foot below the source but 3400. Nay if there were a Siphon passing from the surface of the Earth to the Center and thence rising to the surface again it would convey Water from the one place to the
that most easily OBSERVATION VIII THere hath been much inquiry made by some anent the reason why the dead body of a man or beast riseth from the ground of a Water after it hath been there three or four days But though many have endeavoured to solve the question yet the difficulty remains and in effect it cannot be answered without the knowledge of the foregoing Doctrine anent the nature of fluid Bodies To find out the reason then of this Phenomenon consider that all Bodies are either naturally heavier then Water as Stone and Lead or naturally lighter as Wood and Timber If they be heavier they sink if they be lighter they swim Now I say a mans body immediatly after he is drowned his belly being full of Water must go to the ground because in this case it will be found specifically or naturally heavier then Water That 's to say a mans body will be heavier than as much Water as is the bulk of a mans body For pleasing the fancy imagine a Statue to be composed of Water with all the true dimensions of the person that 's dead so that the one shall answer most exactly to all the dimensions of the other In this case if you counterpoise them in a Ballance the real body that 's made up of flesh blood and bones shall weigh down the other But after this dead body hath lien a short time among the Water it presently begins to swell which is caused by the fermentation of the humors of the blood which goeth before putrefaction and after three or four dayes swells so great that in effect it becomes naturally lighter than Water and therefore riseth That is to say take that body that is now swelled and as much bulk of Water as will be the precise quantity of it and having counterpoised them in a Ballance you will find the Water heavier than the body OBSERVATION IX UPon Thursday the 25 of August 1670 the following Experiment was made in a new Coal-sink on the West side of Tranent When the Coal-hewers had digged down about 6 or 7 fathom they were interrupted sometimes with ill Air therefore to know the power and force of the Damp we let down within the Bucket a Dog When he had gone down about 4 fathom or middle Sink we found little or no alteration in him save only that he opened his mouth and had some difficulty in breathing which we perceived evidently for no sooner he was pulled up to the top where the good Air was but he left off his gaping We let him down next to the bottom where he tarried a pretty while but no more change we found in him than before After this we let down a great quantity of Whins well kindled with a bold flame but they no sooner came to the middle of the sink but the flame was in an instant extinguished and no sooner was the Bucket pulled up but they took fire again This was 5 or 6 times tried with the same success If we compare this Observation with the first we will find that all Damps are not of the same power and force but that some are stronger and kills men and beasts in an instant and that others are less efficacious and more feeble and doth not so much hurt and that men may hazard to go down into a Sink where ill Air is even though fire be sometimes extinguished We see next that these Damps doth not alwayes infect the whole Air of a Coal-pit but only a certain quantity for sometimes it is found in the bottom sometimes in the middle And we see lastly that they are not alwayes of long continuance for it is found that though the Air be ill in the morning yet it may be good ere night and totally evanished ere the next day We may add as was noted in the first Observation that these Damps depend much upon the scituation of the winds seing in strong Southerly winds they are frequently in these places OBSERVATION X. OF these many excellent devices that have been found out of late the Air-pump is one first invented in Germany and afterwards much perfected in England by that Honourable Person Mr Boyl who for his pains and industry in making Experiments therewith deserves the thanks of all learned persons Several trials hath been made of late by it some whereof are as follows I took a slender Glass-tub about 40 inches long closs above and open below and filled it with VVater I next inverted it and set the orifice of it just upon the mouth of the Brass-pipe that bends upward thorow the board whereon the Receiver useth to stand and cemented them together At the first exsuction the whole VVater in the Pipe fell down and ran thorow the Brass-conduit to the Pump Having for a short while stopped the passage and thrust down the Sucker I next opened it again and the Pump being full of VVater it was driven with a considerable force up thorow the Pipe yet was it not compleatly fill'd as before by reason of some Air that I saw in the top After this was done with pleasure five or six times I opened the Stop-cock more quickly than I had used but the VVater by this means was so furiously driven up thorow the Tub that in effect it broke the end of it that was Hermetically sealed and the piece that flew off did hit the seiling so smartly that it rebounded a very far way From this we see the reason why VVater falls not down from Vessels that have narrow necks though they be inverted because it 's kept in by the force and power of the environing Air. 'T is observable that though this Pipe had been 30 foot high yet the whole VVater in it would have subsided and fallen down with one exsuction The next trial was with the help of a small Receiver which in effect was a real Cupping-glass This had a hole made in the bottom of it and was cemented to the Brass-plate and the mouth of it looking upward had a lid for covering of it I took next the lately mentioned Glass-pipe and filled it with good Brandy and having drowned the end of it among stagnant Brandy I set the Vessel wherein it was within the Receiver the Pipe coming up thorow the lid and having cemented it closly I made the first exsuction and found no descent of the Liquor from the top of the Tub. At the second it fell down about an inch At the third it fell down four or five But here appeared a great multitude of small Bubbles of Air like broken VVater near the top of the Pipe within And besides this Phenomenon there ascended from the stagnant Liquor up thorow the Pipe an infinit number of small Bubbles no bigger than Pin-heads for a very large time VVith a fourth exsuction it fell down within two or three inches of the stagnant Brandy And thinking to make the one level with the other I made a fifth but here appeared a strang effect namely
that Decemb. 13. 1669 one Doctor Beal found the Mercury in the Baroscope never to be so high as it was then That same very day I found the hight of it 29 inches and nine ten parts which I never observed before And though the day here was dark and the Heavens covered with Clouds yet no rain for many dayes followed but much dryness and fair weather On Saturday night March 26 1670 I found the altitude no more than 27 and nine ten parts This night was exceeding windy with a great rain On February 1 1671. I found the altitude 30 inches and the Heavens most clear But in the most part of May following I have found the hight but 27 inches and five ten parts in which time there was abundance of rain OBSERVATION XIV NOvember 7. 1670. I made exact trial with the Magnetick Needle for knowing the variation and I found it vary from the North three degrees and a half towards the West Hevelius writes from Dantzick to the Royal Society at London Iuly 5. 1670 that it varies with him seven degrees twenty minuts west OBSERVATION XV. DEcember 17. 1669 I observed with a large Quadrant half 9 a clock at night the formost Guard-star when it was in the Meridian and lowest to have 41 degrees 22 minuts of altitude And on Ianuary 7. 1670 at 7 a clock in the morning I found it when it was in the Meridian and highest to have 70 degrees 27 minuts Hence I conclude the elevation of the Pole here to be 55 degrees 54 minuts 30 seconds and consequently as much at Edinburgh because both the places are upon one and the same Parallel OBSERVATION XVI FOr finding the true Meridian follow this method In some convenient place fix two Wyre strings with weights at them that they may hang perpendicular Then in the night time observe when the fourth star of the Plough begins to come near to the lowest part of the Meridian at which time you will find the Polar star highest Then so order the two strings by moving them hither and thither till both of them cover both the said Stars then shall they in that position give you the true South and North. This observation is the product of the seventh OBSERVATION XVII THere fell out in Mid and East-Lothian on Thursday May 11 1671 in the afternoon a considerable shour of hail with thunder and rain It came from the South-west with a great blast of wind and ran alongs from Picts-land-hills North-east towards the Sea coast The hail were big in several places as Musquet Ball and many of them rather oval than round Some persons suffered great loss of their young Pease others of their Glass Windows Eight or ten days before there was a considerable heat and dry VVeather For 20 dayes after cold Easterly winds with rain every day but especially in the end of the Moneth extraordinary rain and mist. This is so much the more to be observed because in this Countrey seldom such extraordinary hail falls out This year the Agues and Trembling Fevers have been most frequent and to many deadly OBSERVATION XVIII I Did hear lately of a curious Experiment in Germany made by a Person of note which I shall briefly in this Observation let the Reader understand And though I have heard since that it is now published in Print yet I hope it will not be impertinent to mention it here especially for their cause who cannot conveniently come to the knowledge of such things And for this reason also that I may explicat the Phenomena thereof from the foregoing doctrine and demonstrat particularly the true cause of that admirable effect that 's seen in it which I desiderat in the publisher The Auctor then takes two Vessels of Brass each one of them in form of half a sphere of a pretty large size Nothing can more fitly represent them for form and quantity than two Bee-skeps Only each of them hath a strong Ring of Brass upon the Center without and they are so contrived by the Artist that their orifices agree most exactly so that when they are united they represent an intire Sphere almost In one of the sides there 's a hole and a Brass Spigot in it through which the whole Air within is exsucted and drawn out namely by the help of the Air-pump And when by several exsuctions the Vessels are made empty the Stop-cock is turned about by which means no Air can come in And they remaining empty are taken from the Pump and do cleave so fast together that though a number of lusty fellows 12 on each side do pull vigorously by help of ropes fastned to the Rings yet are they not able to pull them asunder And because this will not do it he yokes in 12 Coach Horses six on every side yet are they not sufficient though they pull contrariwise to other to make a separation But to let the Spectators see that they may be pulled asunder he yokes in 9 or 10 on every side and then after much whipping and sweating they pull the one from the other The cause of this admirable effect is not the fear of vacuity as some do fancy for if that were all the Horses in Germany would not pull them asunder no not the strength of Angels It must then be some extrinsick weight and force that keeps them together which can be nothing else but the weight of the invironing Air. Because no sooner a force is applied that 's more powerful than the weight of the Air but assoon they come asunder And so neither six men nor six horses on each side are able to do it but nine or ten on each side makes a separation For understanding the true cause of this Phenomenon we must consider that the Vessels are 18 inches in diameter Iâ— this be then according to the last Experiment there are two Pillars of Air each one of them as heavy as a Pillar of Mercury 18 inches thick and 29 inches long by which they are united Or each Pillar of Air is as heavy as a Pillar 0â— Water 34 foot high and 18 inches in diameter For finding the weight of it in pounds and consequently the weight of each Pillar of Air by which the two Vessels are united follow this method First multiply 9 the semi-diameter of the Pillar by 54 the circumference and this gives you 486 the half whereof is the bounds of the Area namely 243. And because 34 foot contains 408 inches I multiply 408 by 243 the product whereof is 99144 so many square inches are in a Pillar of Water 34 foot high and 18 inches thick Now seing there are 1728 inches in a cubical foot I divide the number 99144 by this number and I find 57 square foot of Water and more And because every square foot weighs 56 pound Trois I multiply 56 by the number 57 and the product is 3192 pound which is the just weight of a Pillar of Water 34 foot high and 18
inches in diameter and which is the just weight also of each Pillar of Air by which the two Vessels are kept together which will be more weight than seven Hogs-heads full of Water This is easily known for seing a quart of our measure weighs seven pound or to speak strictly six pound fourteen ounces seing the Standard-jug of Striviling contains three pound seven ounces of Water a gallon must weigh 28 pound but 16 times 28 is 448. A Puncheon then full of Water weighs 448 pound If then you divide 3192 by 448 you will find more than 7. The 9 horses then upon this side have 3192 pound weight to draw or 199 stone or the weight of seven Hogs-heads full of Water The other 9 horses upon the other side have as much to pull 'T is no wonder then to see so much difficulty and pains to make a separation It is observed that before the Air be exsucted and drawn out of the two Vessels one man is able to pull them asunder with his hands only Nay which is more if he but blow into them as a man doth into a Bladder he will separat them The reason is because the Air within is of as great force as the Air without 'T is observable next that the larger the Vessels be in diameter the more strength is required to pull the one from the other Upon supposition then they were 4 foot wide I verily believe 30 yoke of oxen upon every side would hardly disjoyn them because the weight of each Pillar of Air would be no less than 22844 pound which would take 63 strong horses to overcome the force of it To pull the one Vessel therefore from the other there must be 126 horses that is 63 on every side OBSERVATION XIX THough this Observation may seem useless because the Proposals that are mentioned in it cannot be made out and brought to pass the Author having died before he had encouragment to prosecute them yet for these following reasons I have adventured to insert it here First that others may either be minded to find out if possible his inventions or set a work to find out somethings that may be as useful Next because he was one of this same Nation and a great Master of the Mathematicks not only in the Speculative but in the Practical part chiefly and admirable for invention And for this cause principally I have presumed to mention his designs and proposals which were found among his Notes after his death which are here insert as they were written with his own hand and offered to the publick not only at home but abroad to strangers There have been men in all ages famous for some one Art and Science beyond others as Apelles for Painting Hippocrates for Medicine Demosthenes for Oratry but who have been more famous in their time than some persons for their profound knowledge in Astronomy Geometry and the other parts of the Mathematicks What an admirable person was Archimedes for his divine knowledge both in the Speculative and Practical part Yet it was not his speculations simply though excellent that did so much commend him as his Inventions and admirable Engines for peace and war as is clear from the Romane Histories and others I confess the Students of these Arts are not so much in request now at least amongst some and that knowledge is not so much esteemed and the reason may be because some who profess themselves great Masters study nothing but the pure speculations which sometimes are to small purpose others before knowing the same unless for perfecting of the mind and giving to a man some private satisfaction But such things will never commend a man so much as the practical part and new Invention will do 'T is surely a small business for one to do nothing but to nibble at some petty Demonstration But when such speculations are joyned with invention and practice for the profit and use of men among whom they live then are they far more to be commended And if this be not such knowledge is of small advantage to themselves or others Many of the Ancient and late Astronomers have been and are famous for practice as witness the indefatigable pains they have been at in making their Observations What hath so highly commended Merchiston over all Europe as his inventions especially his Logarithmes And if all be true that 's reported which I am apt to believe he might have been more renowned for his many excellent Engines which though useful yet because hurtful to mankind he buried with himself I am confident if the Author of these proposals had had time to have prosecuted them he would have been celebrated in the Catalogue of the most famous Mathematicians of his time But leaving this I shall give you them in his own words but first his Apology These bold proposals will need perhaps an apology to such to whom the causes and circumstances are unknown Let it suffice that the Proposer finding himself between two extreams either to leave unprosecuted this affair for fear of being mistaken by some as impudent or to commit himself openly to the charitable judgement of others who will suspend their censure till they have seen what his endeavours will produce He hath rather chosen this last especially considering that his silence could not answer to his duty which he owes to his Countreys service seing the following Engines may be so useful to it A deduction of the fabrick causes and occasions of these new Engines that set the Inventer a-work would take a long time to discourse upon This Paper therefore is only destined for a short information of their use the rest which could not here be insert without impertinency may be supplied afterwards if need be either by a discourse or by a particular demonstration The Proposer then is of opinion if self-love of his own Inventions do not blind his Judgement that these paradoxes may be truly affirmed That if it shall please His Majesty to arm with these new Arms and Engines 500 Foot or fewer this small number shall be Masters of the Fields in France Germany Spain or where else it shall please His Majesty however encountered by the most powerful Army of Horse or Foot armed with ordinary Arms of Pistol Carabine Pike Musquet which Europe can bring to the Fields The cause of this admirable effect is in the quality of these new Arms by which the whole Horsemen and Footmen of the enemy are rendred useless and unservicable neither can they do any offence to these who are so armed The Musquetteers who can only serve against these Machins shall be put to such disadvantage as it is impossible they can stand the least time in the common way of service with the Musquet it not being able to make one shot for twenty which shall be made from these new Engines These new Arms have this advantage likewise that these who are so armed can by no force of Horse or Foot be broken
THE HYDROSTATICKS OR The Weight Force and Pressure of FLUID BODIES Made evident by Physical and Sensible Experiments TOGETHER VVith some Miscellany Observations the last whereof is a short History of Coal and of all the Common and Proper Accidents thereof a Subject never treated of before By G. S. EDINBURGH Printed by George Swintoun Iames Glen and Thomas Brown Anno DOM. 1672. G. SINCLARI P. Professoris Hydrostatica EDINBURGI Ann. Dom. 1672 Intus se vasti Proteus tegit obice saxi To my very Honourable and Noble LORD ROBERT VISCOUNT of OXFUIRD LORD MACKGILL of COUSLAND c. My Noble Lord THe first application I make is for pardon that I have adventured to prefix your name to the Frontispice of this Work which in it self cannot be thought worthy of your Trust and Protection there being no proportion between the greatness of your Merit and so mean an Oblation save what flows from the Nobleness of the Subjest and the sincerity of his respects who presents it It is truly a part of Philosophy that was never much Cultivated but of late except in a more abstract and subtil way which did render it less useful but is now more improven by sensible Manifestations of the Soveraign Mistriss of Arts NATURE her self There are indeed my Lord many excellent Sciences which do merit the favour of your Lordships studies and by which your Noble Accomplishments might be more improven yet I am bold to affirm you cannot apply your Noble Mind to any part of Philosophy where you will find more Pleasure with less Pains more evidence of Reason with less Difficulty The famous Gregorio Leti was so much an admirer of your Vertues that he sheltered under your Patrociny his Vita Di Sisto quinto Pontefece Romano And if you were able to protect an envyed Italian in Italy much more may I expect full security from your Name in Scotland where your interest and relations are so considerable And if he who only look'd upon your Vertuous Mind while it was but blossoming was so much perswaded to judge none more fit to Receive Protect and Claim his Labours much more I who have seen the accomplishment of your Vertues at home I have likewise very much confidence of your Noble and Candid Disposition to admit this into your Favour and assurance of your Affection and Skill to Love it and Understand it both which are conspicuous the first in your encouragement to all Learning the other in your Capacity and Understanding to comprehend whatever you encourage Though my Lord I have been much emboldened to offer this Dedication to your Lordship upon the account of your own Heroick Vertues yet I must not pass over in silence a most special Motive which to me shall be the last sparing to express all the great Causes oblieging me so to do and that is the Memory of your VVorthy and nearest Relations who are my Lord your Father Grandfather and Great-Grand-father not only memorable for their Vertue and Learning and peculiar Endowments whereby they were thought worthy to serve their King and Countrey in Council and Honourable Courts of Iustice for these many years but for the Dignity and Antiquity of their famous Ancestours How old your Lordships Name is Buchanan testifies in the close of the Second Book of his History who writeth thus Certè Gildus vetus est in Scotia Nomen ut vetus Mackgildorum sive Mackgillorum gens indicat è cujus posteris honestae adhuc in Scotia Anglia sunt familiae That is Surely Gild is an ancient Name in Scotland as witness the old Family of Mackgilds or Mackgills of whose Posterity there are yet in Scotland and England many Families of good account And as an instance of this the same Author tells us of the Great Thane of Galloway Mackgillum Gallovidiae longè Potentissimum in the life of Mackbeth who by this Vsurper was put to death for his adherence to his Prince from whom your Lordship and your worthy Progenitors are Lineally descended and of whom Buchanan meant in the foregoing passage since our Predecessors flourisht in his time your Great-Grand-Father having then been His Majesties Advocat his Brother Lord Register Having now my Noble Lord laid before you so many considerable Motives which I humbly desire may prevail I cannot but make my next Application for Acceptance and seriously intreat this Work may be received into the Tuition of your Favour and get a full Protection from the Censorious and being enlightned with the splendor of your Name and receiving the impression of your Authority upon it may safely pass thorow the VVorld for which singular Favour I shall fervently wish to your Self and Noble Family all Prosperity and Happiness and shall think my self very happy under the Character of Edinburgh May 20. the day of your Lo. Birth and Majority 1672. My Noble Lord Your Lo. most humble and much oblieged Servant GEORGE SINCLAR TO THE READER Courteous Reader I Shall not detain thee entry with a long Preface but give a short account of what is needful to be known of the Cause Occasion and Matter of the following Treatise After the publication of my last Piece about the Weight and Pressure of the Air I found it needful to treat of the Pressure of the Water because of the near relation between the two the operations and effects of both depending almost upon the same Principles and Causes And that there are many things which cannot throughly be understood of the Pressure of the Air without the knowledge of the Pressure of the Water therefore to make the first the more evident I have spoken of the second the effects and operations of Hydrostatical Experiments being more conspicuous and sensible then the effects and operations of the other The Occasion was some spare time I had now and then for making some Trials part whereof are published here the rest being rather some productions of Reason attentively exercised on that Subject which notwithstanding may be called Experiments though never actually tried nor haply can be because of some accidental impediments yet supposing they were I make it evident that such and such Phenomena would follow whence many necessary conclusions are inferred As for the subject matter there are first moe then thirty Theorems in order to the Pressure of Fluid Bodies as Air Water and Mercury which in effect are nothing else but so many conclusions rationally deduced from various and diverse effects of Aerostatical Hydrostatical and Hydrargyrostatical Experiments which for the most part I have tried my self There are next twenty Experiments briefly described by their own distinct Schematisms their Phenomena according to the Laws of the Hydrostaticks are salved and several new conclusions inferred A Proposal is likewise made of a more convenient Engine for Diving Here several difficulties are proposed and answered and all the obvious Phenomena of Diving explicated If the Lead which sinks the Ark be judged too weighty and big which may render it not
A lighter Fluid is able to press with as great burden as a heavier Figure 2. THis Proposition is true not only of VVater in respect of Mercury but of Air in respect of them both for albeit Air be a thousand times lighter then VVater yet may it have as great a Pressure with it as VVater as is evident from this second Schematism where by the Pressure of the outward Air G H A B twenty nine inches of Mercury O P are supported as well as the twenty nine inches E O by the Pressure of the VVater A B E F. So doth the same Air sustain the thirty four foot of VVater N R which are really as heavy as the twenty nine inches of Mercury O P. Now if the weight of the Atmosphere be equivalent to the weight of thirty four foot of Water or of twenty nine inches of Mercury 't is no wonder to see Water press with as great weight as Mercury which is likewise cleaâ— from this same Figure where by the Pressure of the Water A B E F twenty nine inches of Mercury E O are suspended as truly as the Mercury C E within the lower end of the Pipe is supported by the outward invironing Mercury The reasons of these Phenomena are taken from the altitudes of the pressing Fluids for though a Body were never so light yet multiplication of parts makes multiplication of weight which multiplication of parts in Fluids must be according to altitude for multiplication of parts according to thickness and breadth will not do it Observe here that if as much Air as fills the Tub between N and L were put into the scale of a Ballance it would exactly counterpoise the thirty four foot of Water N R poured into the other scale Item that as much Water as will fill the Tub between E and A is just the weight of the Mercury E O. Lastly that as much Air as will fill the Pipe between O and G is just the weight of the Mercury O P. THEOREM XXVIII The Pressure of Fluids doth not diminish while you subtract from their thickness but only when you subtract from their altitude Figure 1. FOr understanding this let us look upon the first Schematism where there are four Pillars of Water Now I say though you cut off the three Columes of Water upon the right side yet there shall remain as much Pressure in the quadrat foot of VVater Q as was while these were intire But if you cut off from the top the VVater E F G H then presently an alteration follows not only in the lowest parts nigh to the bottom but through all the intermediat parts for not only the VVater Q loseth a degree of its Pressure but the VVaters P and O suffer the same loss This Theorem holds true likewise in order to the Element of Air. For if by Divine Providence the Air should become less in Altitude than it is then surely the Bensil of the ambient Air that we breath in and out should be by proportion weakned also And contrariwise if the Altitude became more then stronger should the Bensil be here with us in the lowest parts both which would be hurtful to creatures that live by breathing For if the Altitude of the Air were far more then it is our bodies would be under a far greater Pressure which surely would be very hurtful And upon the other hand if the Altitude of the Air were far less then it is we should be at a greater loss for then by reason of the weak Bensil we would breath indeed but with great difficulty THEOREM XXIX A thicker Pillar of a Fluid is not able to press up a slenderer unless there be an unequal Pressure Figure 3. FOr understanding this let us suppose this third Schematism to represent a vessel with VVater in it as high as A B among which is thrust down to the bottom the Pipe G H open at both ends I say then the two thicker Pillars of Air E A and F B pressing upon the surface of the VVater A B are not able to press up the Water H I or the slender Pillar of Air I G within the Pipe the one higher then I the other higher then G. If it be said they are heavier because they are thicker I answer they are truly heavier for the Pillar of Air F B apart will be thrice as heavy as the slender Pillar of Air I G. But if you reckon the Pillar of Air E A upon the left hand both together will be six times heavier then the Air I G yet are they not able either severally or conjunctly to press up the Water H I higher then I or the Air I G higher then G. For solving this difficulty I must say conform to the fourth Theorem that Fluid Bodies counterpoiseth one another not according to their thickness and breadth but according to their altitude only therefore seing the slender Pillar of Air I G is as high as either F B or E A it cannot be prest up by them For by vertue of this equal hight all the three press equally and uniformly upon the surface of Water A B and therefore according to the twelfth Theorem there can be no motion But if so be the Pillar F B were higher then the Pillar I G then surely would the Water H I be prest up for in such a case there is an unequal Pressure Or if the Pillar I G were higher then the Pillar F B then surely would the Water I H be prest down there being again an unequal Pressure the Water within the Pipe being more burdened then the Water about the Pipe In a word there 's no more difficulty here then if the Pipe were taken away in which case there would be but one Pillar of Air resting upon the surface of Water A B. If it be said the Pipe being thrust down makes of one Pillar three distinct ones and consequently a formal counter-ballance or mutual sustentation Be it so yet because all these press uniformly there can be no motion THEOREM XXX Fluids press not only according to perpendicular Lines but according to crooked Lines Figure 4. FOr proving this Proposition let us suppose A B C D to be a large Vessel full of VVater as high as A N B and a little Vessel lying within it near to the bottom closs above at M but with an open orifice downward as G and having other two passages going in to it upon the right and left side as E O and F P. Now I say the Pressure of this VVater is not only from N to M in a Straight line downwards but from E to O and from F to P by crooked lines Nay put the case this Vessel had no passage in to it but by a Labyrinth or entry full of intricate windings yet the Pressure will be communicated thorow all these even to the middle of it and which is more the VVater H or I within the Vessel would be under the same
degree of Pressure with the VVater E or L without or with the VVater K or F. And which is strange let us suppose both the entries E and F stopped and nothing remaining open but the hole G which I judge no wider then may admit the hair of ones head yet thorow that smal hole shall the Pressure be communicated to the parts of the Water within in as high a degree as if the upper part of the Vessel E M L were cut off to let the Pressure come down directly What is true in order to Water the same is true in order to Air or Mercury or any other Fluid For though a house were built never so closs without door or window yet if there remain but one smal hole in it the Pressure of the whole Atmosphere shall be transmitted thorow that entrie and shall reduce the Air within the house to as high a degree of Bensil as the Air without THEOREM XXXI The Pressure and Bensil of a Fluid that 's in the Lowest foot is equivalent to the weight of the whole Pillar above Figure 5. FOr understanding this Proposition let us suppose E F to be the lowest foot of a Pillar of Air cut off from the rest and inclosed in the Vessel E F six inches in Diameter or wideness and twelve inches high Now I say the Bensil and Pressure that 's in that one foot of Air is exactly of as great force and power as is the weight of the whole Pillar of Air from which it was cut off Let A B be that Pillar of Air which I suppose is six inches thick and six thousand fathom high Take it and weigh it in a Ballance and say it weighs 500 pound yet the Pressure and Bensil that 's in the Air E F is of as much force and if the one be of strength by its weight to move v. g. a great Clock the other by its Bensil will be of as much This proposition is true also in order to Water For put the case E F were the lowest of 34 foot of Water in it will be found as much Pressure and force as will be equivalent to the weight of the whole thirty three foot from which it was cut off But here occurreth a difficulty for if the Pressure and Bensil of the foot of Air E F be equivalent to the weight of the whole Pillar of Air A B which weighs 500 pound then must the slender Pillar of Air C D that 's but two inches in diameter be as heavy weighed in a ballance as the thicker Pillar A B which is absurd I prove the connexion of the two parts of the Argument thus as the Bensil of the Air G H is to the Bensil of the Air E F so is the weight of the Pillar C D to the weight of the Pillar A B but so it is that the Bensil of the Air G H is equal in degree to the Bensil of the Air E F according to the Theorem 21. Where it 's said that the Pressure of Fluids may be as much in the least part as in the whole therefore the Pillar C D and the Pillar A B must be of equal weight when both are weighed together in the opposite scales of a Ballance which is false seing the one is far thicker and so heavier then the other There 's no way to answer this objection but by granting the Air G H and E F to be equal in Bensil and yet the two Pillars unequal in weight because according to the 22 Theorem the Bensil of a Fluid is one thing and the natural weight is another THEOREM XXXII In all Fluids there is a Pondus and a Potentia a weight and a power counterpoising one another as in the Staticks THat part of the Mathematicks which is called Staticks is nothing else but the Art of weighing heavy Bodies in which two things are commonly distinguished viz. the pondus and the potentia the weight and the power 'T is evident while two things are counterpoising one another in the opposite scales of a Ballance as Lead and Gold the one being the pondus the other the potentia The same two are as truly found in the Hydrostaticks for while the Mercurial Cylinder is suspended in the Torricellian Experiment by the weight of the Air the one is really the pondus the other the potentia Or while into a Siphon with the two orifices upward Water is poured there arises a counterpoise the Water of the one Leg counter-ballancing the Water of the other this taking the name of a pondus the other the name of a potentia 'T is evident also while a surface of Water sustains a Pillar of Water this being the pondus that the potentia Or while a surface of Water sustains a Pillar of Air the Pillar of Air being the pondus and the surface of Water the potentia Or while a surface of Quick-silver sustains a Pillar of Water or Air the surface is the power and either of the two is the pondus or weight as you please THEOREM XXXIII Fluid Bodies can never cease from motion so long as the pondus exceeds the potentia or the potentia the pondus THis is a sure Principle in the Hydrostaticks which will appear most evident while we pass thorow the subsequent Experiments I shall only now make it appear by one instance though afterwards by a hundred In the Torricellian Experiment lately mentioned 't is observed that though the Pipe were never so long that 's filled with Mercury yet the Liquor subsides and falls down alwayes till it come twenty nine inches above the surface of the stagnant Mercury below The reason whereof is truly this so long as the Mercury is higher then the said point as long doth the pondus of it exceed the potentia of the Air therefore the motion of it downward can never cease till at last by falling down and becoming shorter it becomes lighter in which instant of time the motion ends both of them being now in equipondia or in evenness of weight THEOREM XXXIV When two Fluids of different kinds are in aequilibrio together the height of the one Cylinder is in proportion to the height of the other 〈◊〉 the natural weight of the one is to the natural weight of the other FOr understanding this Theorem we must consider that when two Cylinders of the same kind as one of Water with Water or as one of Mercury with Mercury are counterpoising one another both are of the same altitude because both are of the same natural weight But when the two are of different kinds as a Cylinder of Air with Mercury or as a Cylinder of Air with Water or as a Cylinder of Water with Mercury then it will be found that by what proportion the one Liquor is naturally heavier or lighter then the other by that same proportion is the one Cylinder higher or lower then the other For example because Air is reckoned 14000 times lighter then
M G H. The same Phenomenon happens in taking the Air out of the narrow Pipe F K. The reason is still unequal Pressure for in removing the Air that 's within the Pipe the part of the surface M and the part H remaines burthened while the part G is freed of its burden therefore this part of the surface being liberated of its burden that came down through the Pipe instantly rises and climbs up as far as the outward Air resting upon M and H can raise it which is to E 34 foot for the Pressure of the Air upon the surfaces of all Waters according to the 25 Theorem being equivalent to the weight of 34 foot of Water must raise the said Water in the Pipe 34 foot You do not wonder why it rises from I to G as in the first experiment no more ought you to wonder why it rises from G to E seing the weight of the Air doth the same thing that 34 foot of Water resting upon the surface M H would do From this experiment we see first that the Pressure of the Air is the proper cause of the motion of Water up thorow Pumps and Siphons or any other instrument that 's used in Water-works of that kind for if the weight of the Air resting upon the surface M H be the cause why the Water climbs up from G to E the same must be the cause why the stagnant Water followes the Sucker of the Pump while it 's pulled up And the same is the cause why Water ascends the Leg of a Siphon and is the cause why motion continues after suction is ended We see secondly that every Pressing Fluid hath a Sphere of activity to which it is able to raise the Fluid that is pressed This is evident in this experiment because the Pressure of the Air resting upon M H is able to raise the Water the hight of E in the wide Pipe and the hight of F in the narrow and no further even though the said Pipes were far longer and this altitude and highest point is precisely 34 foot between Air and Water We see thirdly that 't is all one matter whether Pumps and Siphons be wider or narrower whether the tub of the Baroscope be wherein the Mercury is suspended of a large Diameter or of a lesser Diameter This is also evident from the same experiment seing there is no more difficulty in causing the Water ascend the wide Pipe than in causing it ascend the narrow one And the reason is because the pressing Fluid repects not the pressed Fluid according to its thickness and breadth but only according to its altitude Therefore ' its as easie for the Air to press up Water through a Pump four foot in Diameter as to press it up through a Pump but one foot in Diameter EXPERIMENT IV. Figure 7. THis Schematism represents a large Vessel full of Water whose first and visible surface is D E H K. The second that 's imaginary is L I six foot below it The third of the same kind is M G six foot lower The fourth is N F O six foot yet lower The last and lowest is A B C. There are here also four Tubs or rather one Tub under four divers positions with both ends open After this Tub D A is thrust below the Water till it ascend as high as D in it lift it up between your fingers till it have the position of the second Pipe E F and then you shall see as the orifice of the Pipe ascends the Cylinder of Water fall out by little and little until it be no longer than E F. Again lift it further up till it have the position of the Pipe H G then shall you find the Cylinder of Water become yet shorter Lastly if it be scituated as the Pipe K I the internal Water becomes no longer than K I. The reasons of these Phenomena are the same namely unequal Pressure for the Orifice A being lifted up as high as F it comes to the imaginary surface N O which is not under so much Pressure as the other is therefore one part of it being more burdened than another namely the part upon which the Cylinder of Water rests it presently yeelds and suffers the Cylinder to become shorter and lighter till it become no heavier then is proportionable to its own strength To make this reason more evident it is to be noted that no surface of Water is able to support a Cylinder higher then its own deepness that is to say if a surface be 40 foot deep it is able to sustain a Cylinder 40 foot high and no more therefore the surface N O being but 18 foot deep it cannot sustain a Cylinder 24 foot long for if that were then the Potentia should be inferiour to the Pondus which is impossible in the Hydrostaticks In effect it were no less absurdity then to say 18 ounces are able to counterballance 24. For a second trial lift up the same Pipe higher till it acquire the position of the Tub G H in this case the Cylinder of Water within it becomes yet shorter even no longer than G H. The reason is the same namely unequal Pressure for when a Cylinder of Water 18 foot high comes to rest upon this surface that is but 12 foot deep it makes one part of it more burdened then another therefore the part that is more prest presently yeelds and suffers the Cylinder to fall down till the Pondus of it become equal to its own Potentia For the last trial lift up the Tub till it acquire the position of the Pipe K I in this case the Water within it becomes no longer then K I the surface L I that is but six foot deep not being able to sustain a Cylinder 12 foot high From this Experiment we see first that in all Fluid Bodies there is a Pressure which is more or less according to the deepness of that Fluid this is evident from the four several surfaces there being more Pressure and force in the lowest A B C then in the next N O and more in this then in the surface M G and more in this then in L I. We see secondly that in all Fluids there is a Pondus and a Potentia which two are alwayes of equal force and strength the Potentia is clear and evident in the surface by supporting the Pillar which Pillar is nothing else but the Pondus supported And that they are alwayes of equal strength is most evident also for when you endeavour to make the Pondus unequal to the Potentia in making a surface 18 foot deep to support a Pillar 24 foot high they of their own accord become equal the Pillar becoming shorter and suitable to the strength of the surface that sustains it We see thirdly that 't is impossible for one part of the same Horizontal surface to be more burdened then another for when you endeavour to do it by setting a longer Pillar upon it the part burdened
instantly yeelds till it be no more prest then the next part to it We see fourthly that the inequality that is between the Pondus and the Potentia in Fluids is the proper cause of the motion of Fluids For when you endeavour to make a surface 30 foot deep sustain a Pillar 40 foot high this inequality is the true cause why the Pillar subsides and falls down and why the surface yeelds and gives way to it And this inequality is the true cause why the motion of Water thorow Siphons continues For understanding this you must conceive a Siphon to be nothing else but a crooked Pipe with two legs the one drowned among Water the other hanging in the open Air. The use of it is for conveying Wine or Water from one Vessel to another which is easily done by suction Now after suction is ended the motion of the Water continues till the surface become lower then the orifice out of which it runs The true reason then why the Water flows out is the inequality between the Potentia of the Air and the Pondus of the VVater the Pondus being stronger then the Potentia For in Air as in VVater we must conceive Horizontal surfaces and these surfaces to be endowed with Pressure and force as are the surfaces of VVater Now when the leg of a Siphon is hanging in the Air it must rest upon one surface or another and consequently the VVater in it must rest upon the same surface If the Potentia of the surface be stronger then the Pondus of the VVater the VVater is driven backward which alwayes comes to pass when the orifice is higher then the surface of the VVater of the Vessel among which the other leg is drowned If the Potentia of the surface of that Air be of equal power and strength with the Pondus of the VVater the VVater goeth neither backward nor forward but stands in equilibrio this happens when the orifice is neither higher nor lower than the surface of the VVater in the Vessel But if the Potentia of the surface of the Air be weaker than the Pondus of the VVater in this case the Air yeelds and suffers the VVater to run out even as a surface 30 foot deep yeelds to a Pillar of VVater 40 foot high The same inequality is the reason why VVater climbs up the Pump why VVater climbs up a Pipe when a man sucks with his mouth Before suction the Potentia that 's in the surface of VVater among which the end of the Pipe is drowned is of equal force with the Pondus of the Pillar of Air that comes down thorow the Pipe or Pump but assoon as a man begins to suck the said Pillar of Air becomes lighter and the VVater finding this presently ascends The same is the reason why the Mercury falls down to 29 inches in the Baroscope and no further for as long as the Pondus of the Pillar of Mercury exceeds the Potentia of the surface of Air so long doth the motion continue and when both are become equal in force the motion ceaseth VVhen the Glass-tub is 40 inches long and filled with Mercury and inverted after the common manner you are endeavouring as it were to cause a surface 29 inches deep sustain a Pillar 40 inches high which is utterly impossible in Fluids It is judged by many a wonder to see the deflux of the Mercury in the Baroscope but in effect there 's no more cause of admiration in it than to see the Cylinder of Water grow shorter by lifting the Pipe up from one surface to another From this Experiment we see the true reason why the Mercurial Cylinder of the Baroscope becomes shorter and shorter according as a man climbs up a mountain with it For at the root of the hill the surface of Air that sustains the Pillar of Mercury is of greater force than the surface at the middle part and this is stronger than any surface at the top The Pipe therefore being carried up from one surface to another the Mercury in it must subside and fall down even as the Water falls down and becomes shorter by lifting the Pipe from the surface A B C D to the surface N O. And as the whole VVater would fall down if the orifice I were lifted above the surface D E H K so if the Baroscope could be carried so high till it came above the top of the Air the whole Mercurial Cylinder would surely fall down And as by thrusting down the said Pipe to the bottom of the Vessel again as the Pipe D A the VVater ascends in it so by bringing down the Baroscope to the earth again the whole 19 inches would rise again EXPERIMENT V. Figure 8. FIll the Vessel A D G H with VVater to the brim Next thrust down the open orifice of the Tub D A to the bottom and you shall see the VVater ascend in it as high as D according to the first experiment When this is done recline the said Pipe till it ly as B E and you shall find the Pipe compleatly full of VVater Next erect the same Tub again as D A and you shall see the Cylinder of VVater fall down and become shorter as at first For salving this Phenomenon and such like I must suppose this VVater to be 50 inches deep and the Tub I A and B E 90 inches long and the said Tub in reclining to describe the quadrant of a Circle F E G. Now the question is why there being but 50 inches of Water in the Tub while erected there should be 60 in it when it is reclined Secondly why there should be 90 inches of Water in the Tub B E and but 50 in it when it stands Perpendicular as D A If you reply because there are 90 inches in recta linea between the point B and the point E and but 50 between A and D. But this will not answer the case because if you stop the orifice E with the pulp of your Finger before it be erected you will find the Tub remain full of VVater even while it stands Perpendicular and fall down when the orifice is opened Or while the Tub stands Perpendicular stop the orifice I and recline it as B E yet no more Water will be found in it than 50 inches but by unstopping the said orifice the VVater climbs up from R to E and becomes 90 inches Now what 's the reason why it runs up from R to E and why it falls down from I to D I answer then the VVater must runâ—up from R to E because of the inequality that 's between the Pondus of the Cylinder B R and the Potentia of the surface of VVater A B C that supports the said Cylinder For understanding this know while the Tub is erected there is a perfect equality between the weight of the Pillar A D and the force or Power of the surface that sustains it seing a surface 50 inches deep supports a Pillar 50 inches
clear from the Bensil of the Air G F which in effect counterpoiseth the weight of the whole Atmosphere resting upon the surface of Water A B. We see secondly that when the pondus and the potentia of two Fluids are in equilibrio or of equal strength a very small addition to either of them will cast the ballance For if a man should but breath softly upon the side of the Glass between G and F or lay his warm hand to it the said Air will presently dilate it self and by becoming thus stronger thrust down the Water and so overcome the potentia of the surface We see thirdly a confirmation of the sixth Theorem namely that the Pressure of Fluids is on every side as is clear from the inclosed Air G F that not only presseth down the Water F D but with as great force presseth up the top of the Glass within and presseth upon all the sides of it within with the same force This Experiment also leads us to the knowledge of two things First of the reason why with cold the Water ascends in the common Weather-glasses and why in hot weather the Water descends Secondly from this Experiment we may learn to know when the Air is under a greater Pressure and when under a lesser because when the Air becomes heavier as in fair weather the Water creeps up in some measure it may be two or three inches when there is no alteration as to heat and cold and in foul weather or in great winds when the Air is really lighter the said Water creeps down as much If it be asked how shall I know whether it be the cold of the Air or heaviness of the Air that causeth the Water to ascend and whether it be the heat of the Air or the lightness of the Air that causeth the Water to descend I have proposed this question of purpose to let you see a mistake Many believe that the ascent and descent of Water in common Weather-glasses is allanerly from the heat and coldness of the Air and therefore they conclude a cold day to be because the Water is far up whereas the Water hath ascended since the last night by reason of a greater weight in the Air which alwayes is when the weather is dry and calm though there hath been no alteration of heat to cold If it be asked how come we to the knowledge of this that the pressure and weight of the Element of Air is sometimes less and sometimes more I answer this secret o Nature was never discovered till the invention of the Torricellian Experiment otherwise called the Baroscope For after the falling down of the Quick-silver to 29 inches if you suffer it to stand thus in your Parlour or Chamber according as the Pressure and weight of the Element of Air becomes more or less so will the Altitude of the Mercury become less or more and vary sometimes above 29 inches and sometimes below This alteration is very sensible which is sometimes the tenth part of an inch sometimes the sixth and sometimes the third according as the weight of the Air is less or more From December to February I found the alteration become less and more from 30 inches to 28 which will be three fingers breadth The common Weather-glasses then are fallacious and deceitful unless they be so contrived that the Pressure of the Air cannot affect them which is easily done by sealing them Hermetically and in stead of common Water to put in Spiritus Vini rectificatissimus or the most excellent Spirit of Wine and strongest that can be made It may be here inquired whether or not Mercury would ascend in this Glass as the Water does I answer it would because the ascent depends only upon the Pressure of the Air incumbing upon the stagnant Liquor in the Vessell that 's able to drive up Mercury as well as Water It may be inquired secondly how far Mercury will ascend and how far Water will creep up I answer Mercury can ascend no higher in a Tub than 29 inches and Water no higher than 34 foot and this onely happens when there is no Air above the tops of the Cylinders to hinder their ascents But when there is Air as G F above the liquor it can go no higher than the point to which the cold is able to contract the inclosed Air which is in this Glass the point F. It may be inquired thirdly which is the greater difficulty whether or not Mercury will rise as easily in a Tub as Water for seeing it s 14 times heavier it seemes the Air should have greater difficulty to press it up than to press up Water I answer 't is greater difficulty for the Air to press up 20 inches of Mercury than to press up 20 inches of Water yet it s no greater difficulty for the Air to press up 20 inches of Mercury than to press up 23 foot of Water because the burden and weight is the same It may be inquired fourthly whether or not it be as easie for the Air to press up a thick and gross Cylinder of Water as to press up a thin and slender one For example whether is it as easie for the Air to press up a Cylinder of Water 10 inches in Diameter and 10 foot high as it is to press up one two inches in diameter and 10 foot high I answer there is no more difficulty in the one than in the other and the reason is because Fluid bodies do not counterpoise one another according to their thickness but only according to their altitude according to the fourth Theorem Therefore seeing the slender Cylinder is as high as the grosser it must be no more difficult to the Air to press up the one then the other There is one difficulty yet remaining which is truely the greatest of all namely what 's the reason why its more difficult to the Air to press up 20 inches of Mercury than to press up 20 inches of Water or more difficult to the Air to press up 20 inches of Mercury than to press up 10 I answer this comes to pass because the Air is more burthened with 20 inches of Mercury than with 10. Now if this be then surely it must be more hard to the Air to do the one than to do the other even as it is more hard for a man to lift up from the ground 20 pound of iron than to lift up 10 or 15. The case may be better illustrated after this manner Suppose a man standing on the ground with a rope in his hand coming down from a Pulley above drawing up a weight to the top of the house put the case likewise the weight be a stone of 20 pound and the weight of it to increase successively as it is pulled up Now its easie for the man to pull up the stone the first fathom because it is but 20 pound weight but the stone becoming 40 pound in the second fathom and 60 in the third and
80 in the fourth and so forth untill it become 1000 he will find the greater difficulty the longer he pulls 'T is just so with Air or Water raising Mercury in a Tub for as the Cylinder of the Mercury grows higher by rising so it becomes heavier and consequently the imaginary surface upon which the Base of the Pillar rests is more and more burdened and so becomes less and less able to press it up This leads us to a clear discovery of the reason why 't is more difficult by suction to pull up Mercury in a Pipe than to pull up Water and more hard to suck up ten foot of Water then to suck up five For trial of this which is soon done take a slender Glass-pipe 30 or 40 inches long open at both ends and drown the one end among Quick-silver and put your mouth to the other and having sucked you will find greater difficulty to pull up thorow the Pipe 15 inches of Mercury than to pull up 10 or 8 and far greater difficulty to suck up 20 than to pull up 15. It may be objected that if a man had strength sufficient in his Lungs to suck out the whole Air of the Pipe thirty inches of Mercury would come as easily up as three which seemes to prove that the difficulty of the Mercurie's up-coming depends not upon the weakness of the Air but upon the weakness of the Lungs and want of strength to suck I answer though a man were able to suck out the whole Air of the Pipe yet 30 inches will never ascend so easily as ten nor ten so easily as three and that for the reasons already given But why is it then say you that the stronger the suction be the higher the Mercury ascends in the Pipe I answer the suction serves for no use but to remove the impediment that hinders the Mercury from coming up which is nothing else but the Air within the Pipe Now the more of this Air that 's taken away by suction the stronger the suction is the more Air is taken away the â—arder up comes the Mercury But why ought there to be difficulty in the suction of Mercury to the altitude of 15 or 20 inches more than in the suction of Water to that altitude I answer when I suck Water up thorow a Pipe the suction of the Air above it is easie because the ascending Water helpes much to drive it up to the mouth the outward Air driving up both But the suction is difficult in Mercury because the ascending liquor does not help so much to drive up the Air to the mouth as the Water does And the reason is because the Air being more burdened with 15 inches of Mercury than with 15 inches of Water cannot so easily drive up the one as the oâ—her and so Mercury cannot so easily drive up the Air of the Pipe to the mouth as Water does In a word according to the difference of specifick weight between Water and Mercury so is the difficulty of suction therefore because Mercury is 14 times heavier than Water there is 14 times more difficulty to pull up the one than the other Note that suction is not taken here strictly as contradistinguished from pulsion but in a large sense as it may comprehend it To proceed a little further let us suppose the Pillar of Mercury see the 11. Figure G H that 's raised by the surface of Air F G to be 29 inches and every inch to weigh one ounce Secondly that the said surface has 29 degrees of power or force in it for in all counterpoises the Pondus and the Potentia are equal therefore if the Mercury be 29 inches the Potentia of the surface must have 29 degrees of strength or force in it to counterballance the Pondus These things being supposed which are evident let us imagine the surface of Air to raise the Mercury one inch above F G. In this case the surface is weaker than it was which I prove evidently because it is now but able to raise 28 of Mercury Imagine next the said surface to have raised the Mercury two inches above F G then it follows that it must be yet weaker because it 's now but able to raise 27 inches for by supporting two ounce of the Pondus it loseth two degrees of it's own Potentia In raiâ—ing three inches of Mercury it is three degrees weaker and in raising four it is four degrees weaker and so forth therefore having raised 28 inches there is but one degree of force remaining in the surface And when it hath raised the whole namely 29 it is no more able and can no more press For confirmation put the case that the surface of Air F G were as able and had as much Pressure in it after it hath raised 29 inches of Mercury as it is after the raising of 10 then it follows of necessity that after the raising of 20 it shall raise 19 moe which is impossible seing the greatest altitude is 29. It follows of necessity I say because after the raising of 10 it is able to raise 19 moe therefore if it be as able after 20 as after 10 it must raise 19 after 20. Yea if it be as able after 20 as 10 it must be as able after 29 as 10. If this be then it may raise other 29 and a third 29 and so in infinitum Therefore I conclude that when two Fluid Bodies are in equilibrio one with another or when the pondus is equal to the potentia none of them doth actually press upon another at least the surface hath lost all its Power and Pressure which is also evident in the Pillar For understanding this let us suppose A C B Figure 11. to be a Pipe 58 inches long and full of Mercury and every inch of it to weigh one ounce Now when the orifice D is opened there is here as great an inequality between the pondus and the potentia of the surface of Air E B on which it rests as was between the surface F G and the pondus of Mercury H G. For as F G had 29 degrees of power to raise G H so the Pillar A B has 29 ounce of weight to overcome the surface E B. And as the surface F G became one degree weaker by raising one inch of the Mercury H G and two degrees weaker by raising two inches and so forward till it lost all its Pressure so the Pillar by falling down one inch loseth one ounce of the weight by falling down two it loseth two ounce and so forward till by falling down from A to C it loseth all its Weight and Pressure But here occurreth a difficulty for if the surface F G hath lost all its Pressure by raising the Mercury from G to H and if the Pillar C B hath lost all its Pressure by falling down from A to C it follows that when a Pillar of a Fluid and a surface of a Fluid are in equal termes or brought to
plain had as many holes cut through it answering to the four of the nether Secondly what would folow if the nether plain were intire and four bored through the upper But I shall supersede and leave these to be gathered by the judicious Reader From this Experiment we see first that the broader and larger a surface of a Fluid be it 's the more able to sustain a burden and the narrower it be 't is the less able Secondly that each part of a surface is able to sustain so much weight and no more and no less From what is said we shall only inâ—err this conclusion that equality of hight between Pillars of a Fluid makes equal Pressure and inequality of hight makes unequal Pressure Therefore 't is no matter whether they be gross or small thick or slender provided they be all of the same Altitude EXPERIMENT XIV Figure 20. THis Schematism represents a Vessel full of Water 8 foot deep E F is a Glass-Pipe open at both ends about 9 foot high and one inch in Diameter A B C D is a Vessel of Glass or of any other metal thorow whose orifice above the said Pipe comes down B H I is a Pipe going out from the said Vessel crooked with a right angle at H that the orifice I may look upwards That some Hydrostatical conclusions may be inferred from this Experiment fill the lower Vessel A B C D with Quick-silver almost then pour in as much Water above it as will fill the space A B H leaving from H to I full of Air. Next thrust down the orifice of the Pipe E below the said Water and Mercury till it rest upon the bottom C D. Lastly stop well with cement the passage of the lower Vessel through which the Pipe came down that neither Air nor Water may go out or come in These things being done let down this Engine to the bottom of the large Vessel which as was noted is full of VVater from M N to K L 8 foot and you will find the Mercury to rise in the Pipe from A B to G 6 inches and more The reason is because there is a Pillar of VVater K I that enters the orifice I and presseth down the Air from I to P 3 inches which before was 6. This Air being so burdened instantly presseth forward the VVater H B A and this pressing the surface of the stagnant Mercury A B causes the liquor run up the Pipe from A B to G 6 inches The reason why it riseth 6 inches is this between the surface of the stagnant Mercury A B and the top of the Water L O K are 84 inches Now Water being 14 times naturally lighter then Mercury there must be 14 inches of Water required for sustaining one inch of Mercury and consequently 84 for supporting 6. For a second trial lift up the whole Engine to the top of the Water and you will find the 6 inches of Mercury B G sink down and become no higher within the Pipe than the surface of the stagnant Mercury A B without The reason is because by coming up above the Water the Pressure of the Water K I is taken away from the orifice I by which means the comprest Air H P extending it self to I liberats the Water A B H of the Pressure it had and this freeth the Mercury of its Pressure and so the 6 inches falls down For a third trial stop closely the orifice I and let all down as before In this case you will find no ascent of Mercury from B to G because the Water K I cannot have access to thrust down the Air from I to P as formerly For a fourth open the said orifice I while the Engine is below the Water and you will find the Mercury rise from B to G because the Pillar of Water K I hath now access to press For a fifth trial stop the orifice I and bring up all to the top and you will find the six inches of Mercury B G suspended as if the Engine were under the Water The reason is because the stopping of the orifice keeps the inclosed Air P H under the same degree of Pressure it obtained from the Water K I. For a sixth proof open the same orifice I while the Engine is above the Water and you will find the six inches of Mercury fall down because the imprisoned Air H P obtains now its liberty and expanding it self from H to I eases the Water B H of the burden it was under For a seventh pour in 14 inches of Water at the orifice F till it rest upon the top of the Mercury at G and you will find one inch fall down Pour in as much and two inches falls down In a word pour in as much Water as will fill the Pipe to O and you will find the whole six inches fall down The reason is because the Water K I is not able to sustain both the six inches of Mercury and the Water that 's poured in any one of them being able and sufficient to counterpoise it For an eighth trial empty the Pipe of the said Water and after the Mercury is ascended from A B to G as formerly suck out the whole Air between G and F and you will find the Mercury to rise from G to R 29 inches The reason of this is evident from the Pillar of Air S K that rests upon the top of the Pillar of Water K I for by sucking out the said Air you take away the pondus or weight that counterpoised the weight of the Pillar S K therefore it finding its counterpoise removed presently causeth the Water K I to enter farder within the crooked Pipe till it hath prest up the liquor to R. For a ninth trial take the six inches of Mercury B G and put them into the scale of a ballance then take as much Water as will fill the Tub between A B and O and put it into the other scale and you will find a most exact counterballance between them The reason is because if the Water K H or a Pillar of that hight be able to raise and counterpoise the Mercury B G then must as much Water as fills the Pipe betwen B and O be the just weight of it The reason of this consequence is because these two Waters are of the same weight therefore if the one be the just weight of it the other must be so too If it be said that the Water that fills the Pipe between B and O is far thicker then the Water K H therefore they cannot be both of one weight I answer equality of altitude in this Ballance of Nature is equality of weight therefore seing the one Water is as high as the other they must be both of one weight If it be said that a Pillar of Water between K and H cannot counterpoise the six inches of Mercury B G both being put into a ballance and the reason is because the one is thicker than the
far narrower diameter with an orifice H. There is also an orifice at L with a neck about which is knit a small chord M L for letting down this Engine to the bottom of the VVater A B. For trials cause fill the wide glass with Mercury from P to K and you will find it rise in the narrow Pipe as high as the orifice H. This being done close hermetically or with good cement the orifice L then by help of this chord let all go down from the surface C D till it be exactly 17 foot from the top and you will find the Mercury thrust down in the narrow Pipe from H to R 14 inches and an half Let it down next as much and the Mercury will be yet further thrust down namely from R to N the part H R N being full of Water For understanding the reason of this consider that between N and E are 34 foot for so high is the slender Pillar of Water that comes from the top and entring the orifice H comes down thorow the Pipe to N. Consider next that between the said Pillar of Water and the Mercury N P K there is a counterpoise but this counterpoise cannot be unless the Pillar of Water be 34 foot high seing between N and K are 29 inches of Mercury for each inch thereof requires 14 of Water Upon this account it is that when the glass is 17 foot drowned 14 inches and an half are thrust down from H to R. If it be objected that the Pressure and Bensil of the inclosed Air I K is equivalent to the weight of other 29 inches and therefore the Pillar of Water E H R N must be 68 foot high before a counterpoise can happen I answer 't is true that 's said but you do not consider that there is a Pillar of Air F E resting upon the top of the Pillar of Water that makes a compensation exactly To speak then truely and really the 29 inches of Mercury N P K have the weight of 58 inches and the 34 foot of Water E H R N have the weight of 68 foot For a third trial let down the glass 6 foot further and you will find the Water pierce up thorow the thick Cylinder of Mercury P K and rest upon the top K. The only difficulty is to determine how much will spring up before the motion of it cease 'T is evident that the Water will ascend because coming to the Base of a thick and gross Cylinder that it cannot intirely lift it must pierce thorow it seing the force of such a Pillar of Water is now much stronger than the Mercury for in effect the glass being drowned 6 foot further the Pillar that comes down thorow the slender Pipe hath the just weight of 34 inches of Mercury but 29 cannot resist 34 therefore the Water not being able to lift it by reason of the disproportion that 's between the thickness of the one and the slenderness of the other it must pierce up thorow it For clearing this difficulty consider that this glass cannot go down from one imaginary surface to another v. g. from 34 foot where it was till it come to 40 where it now stands but there must be an alteration in the equipondium seing by going down the Pillar of Water E H R N grows higher and consequently heavier and therefore some VVater must pierce up thorow the Mercury for making a counterpoise for 't is impossible for two Fluids to counterpoise one another unless they be in equilibrio Consider secondly that after the Water is come to the top of the Mercury at K it will find difficulty to find a room for it self seing the space between S and I is full of Air. Notwithstanding of this it must ascend I say then after the glass is gone down from 34 to 40 foot there will be about four inches of VVater above K which have reduced the 29 inches of Air K I to 25 S I. If it be asked between what two things is the equipondium now I answer the first was at R between E H R and R N P K. The second was at R between N R H E and N P K. The third is now at S between the 25 inches of inclosed Air I S as one Antagonist and the four inches of Water S K with the 29 inches of Mercury K P and the Water P N R H E as the other To make a fourth equipondium sink the Glass other six foot till it be 46 foot from the top C D then must some more VVater spring up thorow the Mercury this of necessity must be seing the Cylinder of VVater N R H E is six foot higher and so far heavier than it was if this be then must the 25 inches of Air I S be reduced to less quantity seing 'tis impossible for one Fluid to become heavier unless its opposite and antagonist become heavier too for an equipondiums sake Note that the Air I S will not lose other four inches with this six foot of VVater as it did with the former The reason is because if for every six foot the Glass goeth down the Air were comprest four inches it were easie at last to reduce it to nothing for if six reduce it to four and 12 to eight 38 ought to reduce it to no inches which is impossible Therefore I judge it must suffer compression by a certain proportion as we see upon a Scale the divisions of Artificial or Natural Sines grow less and less there being more space between 1 and 2 than between 2 and 3 more between 2 and 3 than between 3 and 4 and so upward till you come to 90. Therefore the second six foot must reduce the 25 inches not to 21 but to 23 circiter and so forth By the which means though the Glass should go down in infinitum yet the Air shall never be reduced to nothing and there shall still some small quantity of VVater come up Or in such a case the Air may be so comprest that it can be no more all the disseminate vacuities being expelled But suppose this to be at 1000 fathom then at 1500 where the Pressure is stronger there can be no equipondium which is absurd for where the pondus becomes stronger the potentia ought to grow stronger likewise I answer the motion of condensation ceaseth indeed but there still remains a potentia or rather in such a case a perfect resistentia whereby the Air is able to resist the greatest weight imaginable before it can be reduced to nothing or suffer a penetration of parts that 's to say two parts to be in one space From the explication of these Phenomena we conclude first that in Water there is a considerable Pressure seing in letting down the Glass 17 foot the Mercury is prest down from H to R and from R to N in going down other 17 foot Secondly that 29 inches of Mercury are as heavy as 34 foot of VVater because the Mercury
K P N makes a just equipondium with the VVater E H R N. Thirdly that Fluids not only of the same kind but of different kinds do counterpoise one another according to altitude and not according to thickness because though the Mercury K P N be far thicker than the VVater E H yet they counterballance one another because a proportion is kept according to their altitudes Fourthly that a Fluid naturally lighter may move a Fluid naturally heavieâ— and thrust it out of its own place because the Water coming in at H thrusts down the Mercury to R and from R to N and so forth Fifthly that of two Fâ—uids unequal in strength debating together the weaker of necessity must yeeld to the stronger though the weaker be far heavier naturally than the stronger as is evident in the Mercuâ—y that yeelds to the Water Sixthly that it is impossible for two Fluids so long as they are unequal in strength to cease from motion till they come to an equipondium because the Water alwayes springs up thorow the Mercury till an equal Ballance happen Seventhly that one Fluid of this kind can counterpoise another Fluid of the same kind though there be divers Fluids interveening because the Air F E counterpoiseth the Air I K or I S notwithstanding of Water and Mercury interveening Eighthly that there may be as much Pressure in one inch of a Fluid as in a million because the 29 inches of Air I S have as much Bensil in them as is in the whole Pillar of Air E F that goeth up from the top of the VVater to the top of the Atmosphere Ninthly that when one Fluid is under Pressure the next must be under the same degree of Pressure though they be not of the same kind but of different sorts because the Air I S the Water S K and Mercury K P are surely under the same degree of Pressure otherwise the motion could not end Tenthly that when two Fluids of divers kinds do press one another that which is naturally lighter ascends alwayes to the higher place and the heavier to the lowest because the Air I S is above the Water S K and the Water S K is above the Mercury Note that this is not universal but only happens when the lighter Cylinder is slenderer than the other for if the Mercury K P were no thicker than the Water P N R H this would raise it intirely Eleventhly that the compression of Air to less space is not according to Arithmetical progression 1 2 3 4 5 but according to some other proportion which may be called Uniform-difform Note here that though this be true of the Air while it is comprest from a more quantity to a less as here or in a Wind-Gun yet it is not true of the Pressure of the Element of Air which is more and more from the top of the Atmosphere to the Earth according to Arithmetical Progression as in Water We see lastly that the heaviest of Fluids such as Mercury press upward as well as downward because the top of the Mercury K thrusts up the Water K S as well as it thrusts down the Water P N R H. It may be enquired here how far this Glass would go down before the 29 inches of Air I K were reduced to one inch I answer its hard to determine but it seems it ought to go down more than 300 fathom In this case there would be 28 inches of Water above K. Let us suppose the orifice H to be stopped at that deepness and the Glass brought above the Water then when the said orifice is opened in the Air you will find the whole VVater P N R H thrust out and not only this but the whole Mercury P K spring out at the orifice H likewise except a little that remains between N and H the reason is because the 29 inches of Air being reduced to one would be under a very great Bensil therefore the weight being taken away that begat it of its own accord it would expand it self to its old dimensions which it could not do unless both the 28 inches of VVater that 's supposed to be above K and the Mercury K P were thrust out of their places EXPERIMENT XVI Figure 22. THis Schematism represents a vessel full of VVater 84 inches deep namely from L N the first surface to M R the bottom From M to R in breadth are 20 inches There are here also two Glass-Pipes open at both ends the one two inches wide the other half an inch wide Both of them are 85 inches long X Y O is a surface of stagnant Mercury among which the two ends of the Pipes are drowned E C is a Pillar of Mercury six inches in height and so is G D both of them raised to that altitude by the Pressure of the Water upon the surface X Y O. The Pillar E C A is supported by and rests upon the imaginary Pillar A P. And so is the Pillar G D B supported by the Pillar B Q. There are three things that occurres here from this operation of nature to be enquired after First why ought the Mercury to rise in the two Tubs after the Vessel is filled with Water Secondly why rather six inches then seven or eight Thirdly what 's the reason why it rises as high in the wide Tâ—b as in the narrow I answer the Mercury rises from C to E and from D to G by the Pressure of the Water that rests upon the surface X Y O. Before that the Water is poured into the Vessel there is here a most equal and uniform Pressure upon the surface X Y O both without and within the Tub namely from the Air that rests upon it But no sooner is the Water poured in but as soon the Pressure becomes unequal the parts of the surface without the Tub being more burdened then the parts C and D within Therefore the part that 's less prest must rise and climb up till the Pressure become equal for it 's impossible that a Fluid can cease from motion so long as there is inequality of weight between the pondus and the potentia If any doubt let him pieâ—ce the side of the Vessel and when the whole Water is run out he will find E C and G D to have fallen down which clearly proves the climbing up of the Mercury to depend upon the in-pouring of the Water For understanding the reason of the second remember that Mercury as we have often noted is counted 14 times heavier then Water therefore E C must be six inches seing X Y O is prest with the altitude of 84 inches of Water It would be judged no marvel to see the Mercury rise from C to E and from D to G provided the face of the stagnant Mercury were as high as Z F. No more strange it is to see the two Mercuries rise with the Pressure of the Water for in effect and really the said Water is the just weight of as
degree of weight the Water presseth up the Air with the same degree of force and power doeth the Air press down the Water If this were not it would be impossible for a man to go down because of pain For when one part of a mans body is less prest than another there ariseth a considerable pain which sometimes is intolerable as is evident from the application of Ventoso-glasses This equality of weight is the true reason why respiration is so easie Yet 't is to be observed that a man cannot breath so easily in the Ark under the Water as above in the Air not because there is any inequality between the weight of the VVater and the force of the Air but only because the quantity of it is little For when a man sucks in as much Air as fills his lungs the quantity must be diminished if this be the Water must ascend by proportion though insensibly When a man thrusts out the same Air again the quantity is increased if this be then the Water must subside a little both which cannot be without difficulty seing there is a sort of ebbing and flowing both of the Air and of the Water in every respiration But it rather seems you say that this difficulty flowes from the strong extraordinary bensil that the Air is under I answer as long as the pressure of a Fluid is uniform though in a high degree yet there can be no trouble in respiration because with what force soever it is driven in upon the lungs with the same force it is driven out again therefore though the Air we live in were as much again bended as it is yet as is probable we would find no more difficulty in breathing than now There is one thing makes breathing easie under the Water in the Ark namely this when a man sucks in the Air to his lungs his breast and belly goes out and so fills the space deserted by the Air that goes in This makes the ebbing and flowing far less From this equality of weight between the pressure of the VVater and the pressure of the Air we see good ground to say that though the Ark were no thicker in the sides than a thin sawed dale yet there would be no hazard of breaking I am confident though it were no stronger in the sides than a wine-glass that 's soon broken yet it might go down 40 fathom without hazard or danger of bursting This affords good ground likewise to make windows in the Ark covered with glass for if the Pressure be uniform and equal its impossible they can be broken The VVater cannot thrust them inward because the Pressure of the Air is as able to thrust them outward It 's certain the more Air be in the Ark the more easie is respiration therefore it s more easie to breath when the Ark is but down 5 fathom than when it is down 10 or 15. It 's probable a man might live within the Ark it being 40 inches deep and 36 inches wide at the deepness of ten fathom near two houres whereas if it were round and narrow above in form of a Bell he could not continue an hour It were very easie to try how long other creatures might live in it for example dogs and such like or fowls as hens pheasants or doves They might easily be inclosed from coming out for though the whole mouth of the Ark were shut up except as much passage as would receive a mans fist yet it will operate as well that way as the other And there a little door might be made to open and shut at pleasure 'T is observed that by long tarrying under the Water in the Bell the Air becomes gross and misty which hinders a man from seing about him The cause of this are vapors that come from the stomach lungs and other parts of the body especially from the stomach when the ventricle is full of meat It 's not fit then that a man about to dive should eat too much or drink too much especially such liquors as Sack or Brandy that beget many fumes and vapors If a man were necessitated to tarry a pretty while below fresh Air might be sent down from above in bottles or bladders even as much as might fill up the place deserted by the contracted Air. 'T is observed by some that have been under the VVater that their eares have been so troubled that for a long time they have found difficulty to hear distinctly The reason of this must be from the great Pressure the tympanum hath suffered from the imprisoned Air of the Bell. The Organ of hearing is soon troubled especially when a man is near to a great gun when it 's fired And surely when a man is but 34 foot down the Air within the Ark will be of double Bensil put the case the man go down 68 foot or 13 or 14 fathom the Bensil is tripled that 's to say if the Air above have five degrees of Pressure in it the Air of the Bell at 68 foot deep will have 15 degrees of Pressure therefore the tympanum of the ear that 's but a small and thin membran must be sore distressed that is overbended and prest inward even as while a man sets upon a drum head a great weight v. g. a Bullet of Lead or Iron of 20 or 30 pound the skin by this suffers an extraordinary Pressure whereby it is in hazard to be rent 'T is probable if a man should go very far down the tympanum might be in hazard of breaking or being rent in two pieces there being a greater Pressure upon the one side from the Air without than upon the other side from the internal Air within which is thought to be within the tympanum There remains another Phenomenon to be explicated and it 's this the further up the Ark comes from the ground of the Water towards the top the Water within it subsides and settles down more and more towards the mouth The reason of it is because the further up the Pressure of the Water is the less and therefore the contracted Air gets liberty to expand and dilate it self and so thrusts down the Water from P Q to L M. In a word by what proportion the Air is contracted in going down by that same proportion it dilates and opens it self in coming up This lets us see as there is disadvantage in going down from the contraction of the Air so there is advantage in coming up from the dilatation of it Some think that the coldness of the Water is the cause why the Air is contracted in the Ark such are those who deny the Pressure of it But this fancy is easily refuted because in asserting this they must maintain the further down the cold is the greater If this be then far more Air must be contracted in going down from 10 to 15 fathom than in passing from 5 to 10 seing as they say the further down the cold is the greater and therefore
the contraction of the Air must be the greater that 's to say there must be more quantity of Air contracted in the one space than in the other But so it is that the further down the contraction is the less They judge likewise the coldness of the Water to be the cause why the sides of empty Vessels are broken in going down But if this be then a strong Vessel should go no further down than a weak Vessel seing cold can pierce thorow the sides of the one as well as thorow the sides of the other And why is it that a bladder full of wind will go down 40 or 50 fathom without bursting yea 100 and yet a stone-bottle or glass-bottle cannot go beyond 20 or 30 If cold have in it that power to break the sides of a strong bottle it must be far more able to burst the sides of a thin Bladder This difference is clearly explicated from the Pressure of the Water but I defy any man to shew the difference from the coldness of it 'T is to be observed that in all such Experiments of sinking of Vessels as Hogs-heads Barrels and Bottles they must be closs on all sides Therefore if a man desire to know how far down a Glass-bottle is able to go without bursting he must stop the mouth of it exactly with a piece of wood and cement In setting down the dimensions of the Ark I have restricted them to 40 inches high and 36 inches wide But if any man be desirous to enlarge them or make them less he may do it Only 't is to be observed that the larger the Ark be the Foot-stool that sinks it must be the heavâ—er Yet it hath this advantage that it contains much Air which is the great perfection of it One of a lesser size hath this advantage that it 's more tractable and easier to let down and to be pull'd up But these things are best known from Experience or if a man please he may calculate As the Ark is a most useful device for profit so 't is excellent for pleasure and recreation if a man were disposed to see the ground and channels of deep VVaters or were inclined to find out Hydrostatical conclusions a knowledge very profitable and which few have attained to Though it seem somewhat difficult to enter the Ark and go down below the Water yet a little use will expell all fear Then a man may go down with less hazard and fear in the Ark then in the Bell because he may conveniently fasten his hands to each side of the Ark if need were He may conveniently sit as in a Chair all the time of down going and up-coming by fixing a little seat in it he may have windows to look out at his body may be so fixed that there needs be no fear of falling out If a man were desirous to make Hydrostatical conclusions by Diving under the VVater the dimensions of the Ark might be enlarged so that it might conveniently cover a mans whole body by which means having much Air in it a Diver might continue under Water half a day if need were Let us suppose then the hight of it to be 8 foot and the breadth 3 foot or more In such a case a man might continue under the VVater many hours and yet not one part of his body wet for if the Ark be 8 foot high and the man 5 foot in stature at the deepness of 10 fathom the Water can scarce rise 3 foot in it But why may not a man come up every half hour when he finds difficulty to tarry down in a little Ark I answer he may but it 's trouble and pains to pull him up and let him down so frequently And it may so happen that through want of Air in a small Ark he be necessitated to come up before he end his work And leaving the work imperfect he may find difficulty in the second down going to find sometimes the place where he was or the thing he was about to lift v. g. a chest of Gold If it be said that a great weight of Stone or Lead is required to sink an Ark 8 foot high which will amount to 4032 pound weight I answer 't is so indeed but here is the advantage when it is once below the Surface there 's little more trouble then with an Ark of lesser dimensions because of the equipondium that's between it and the weight that sinks it In such a Vessel many trials might be made As first that of the Torricellian-Experiment which is nothing else but a Glass-Tub so many inches long with a Mercurial Cylinder in it of 29 inches high that 's supposed to be kept up at that hight by the Pressure of the Air. If this were taken down about 34 foot 't is very probable the Mercury would rise other 29 inches The reason is because the Air within the Ark that presseth upon the Surface of the stagnant Mercury must be under as much pressure again as the Air above but the Air above is able to support 29 therefore this Air must sustain 58. The reason why the Bensil is exactly doubled is this 34 foot of Water hath exactly as much Pressure in it as the whole element of Air therefore the Air within the Ark being 34 foot down must not only have in it the Pressure of the Air above but the Pressure of the Water likewise this necessarily follows because when two Fluids touch or are contiguous to other the one cannot be under five degrees of Pressure unless the other be under as many According to this reasoning if the Ark go down 68 foot the Mercury will rise from 58 to 87. If to 102 it rises 116. This reckoning is founded upon this namely that Water is 14 times lighter than Mercury and therefore one inch of Mercury requires 14 of Water to support it in a Tub and therefore before Water is able to raise 29 inches of it the Pipe must be 34 foot deep For a second trial blow a Bladder as full of wind as it can hold and having knit the neck about with a Pack-threed place it in the Ark and you will find the sides that hath been stifly bended become flaccid and feeble as if the one half of the Wind had gone out and this will come to pass before the Ark can go down eight or nine fathom The strong bensil of the Air within the Ark is the cause of this for as the Ark goes down the Air grows stronger and so at length becomes of that power and force that it easily overcomes the force and Bensil of the Air of the Bladder and reducing it to less room causes the sides become flagging In this case the said Air that was oval and had the form of the Bladder must become round in form of a Globe because of the uniform Pressure that it suffers from the Air of the Ark. When once the Ark is down 14 or 15 fathom take the
by the agitation of a mans body that sometimes abundance of Air is seen to ascend up thorow the Pipe which in effect makes the Cylinder shorter than it ought to be But if so be the end of the Pipe be immerged among Quick-silver contained in a Glass with a narrow orifice so that it may be stopped compleatly you will find no reciprocations at all And to make all things the more sure the Glass may be filled up either with Mercury or with Water above the Mercury by which means the Cylinder in the down-coming or in the up-going shall remain immoveable Besides the stopping of the orifice of the said Glass you may have a wider Vessel that may receive the same Glass into it and it being full of Water may so cover the sealed orifice that there shall be no hazard of any Air coming in Or this Experiment may be first tried at the root of the Hill and having stopped compleatly the mouth of the Vessel the whole Engine may be carried up to the top where you will find the Mercury subside and fall down so much namely after the said orifice is opened for as the stopping of the orifice at the root of the Hill is the cause why that same degree of Pressure remains in the stagnant Liquor so the opening of it upon the top of the Hill is the cause why it becomes less This Experiment lets us see that the Pressure of the Air seems to be as the Pressure of the Water namely the further down the greater and the further up the less and therefore as by coming up to the top of the Water there is no more Pressure so by coming up to the top of the Air there is no more weight in it which in effect sayes that the Air hath a determinat hight as the Water hath From this Experiment we cannot learn the determinat hight of the Air because the definit hight of the Mountain is not known I know there are some who think that the Air is indefinitly extended as if forsooth the Firmament of fixed Stars were the limits of it but I suppose it is hard to make it out OBSERVATION V. JUne 5. 1670. I observed the Sun within 3 minuts of setting to have a perfect oval figure the two ends lying level with the Horizon His colour was not red as ordinarily but bright and clear as if he had been in the Meridian neither was the Sky red but clear also And by the help of the Pendulum Clock I have observed his body to be longer in setting than it ought by eight minuts and sometimes by ten and his Diameter longer in going out of sight than it ought by two and sometimes by three minuts The reason of these Phenomena must be the Refraction unquestionably OBSERVATION VI. UPon Saturday evening the 30 of Iuly 1670 and the night following till about two a Clock in the Sabbath morning there fell out a considerable rain with great thunder and many lightnings About Sun-set the convocation of black clouds appeared first towards the Horizon in the South-west with several lightnings and the wind blowing from that point carried the clouds and rain over Mid and East-Lothian towards the Firth and Sea-coast About 9 a clock the whole Heavens almost were covered with dark clouds yet the rain was not very great neither were the thunder claps frequent but every fifth or sixth second of time a large and great lightning brake out But before the thunder crack was heard which happened every fourth or fifth minut the lightning was so terrible for greatness and brightness that it might have bred astonishment And because the night was very dark and the lightning very splendid a man might have perceived houses and coâ—n-fields at a great distance And if any had resolved to catch it in the breaking out it did so dazle the eyes that for half a minut he was not able to see any thing about him Sometimes the lightning that went before the thunder brake forth from the clouds like a long spout of fire or rather like a long flame raised high with a Smiths Bellows but did not continue long in sight Such an one above the Firth was seen to spout downward upon the Sea Sometimes there appeared from the one end of the cloud to the other an hiatus or wide opening all full of fire in form of a long furrow or branch of a River not straight but crooked I suppose the breadth of it in it self would have been twenty pace and more and the length of it five or six hundred pace the duration of it would have been about a second of time Sometimes a man might have perceived the nether side of the cloud before the crack came all speckled with streams of fire here and there like the side of an Hill where Moor-burn is which brake forth into a lightning But there was one after which followed a terrible thunder crack which far exceeded all the rest for quantity and splendor It brake out from the cloud being shot from North to South in form of fire from a great Cannon but in so great quantity as if a Gun ten foot wide with 500 pound weight of Powder in it had been fired And surely the lightning behoved to be far greater in it self seeing it appeared so great at so great a distance It did not evanish in an instant like the fire of a Gun but continued about a second and an half by reason it seems that it could not break out all at once This did so dazle the sight that for half a minut almost nothing was seen but like a white mist flying before the eyes The whole Countrey about was seen distinctly All these great lightnings were seen a considerable time before the crack was heard Sometimes 30 seconds numbered by the Pendulum Clock interveened namely when the thunder was at a distance about 7 or 8 miles Sometimes 15 or 16 only interveened But when the thunder was just above our head no moe passed than 7 or 8 which seems to demonstrat that these thick black clouds out of which the thunder breaks are not a Scottish mile from the earth when they are directly above us 'T is observable that in all lightnings and thunderings there is no smoke to be seen which seems to evince that the matter whereof they are generated must be most pure and subtil Who knows but this Countrey that abounds with Coal may occasion more thunder and lightnings than other places namely by sending up sulphurious exhalations to the middle region of the Air wherewith the Coal-mines abound OBSERVATION VII THis is a method for finding out the true South and North Points which are in effect very difficult to know Take therefore four pieces of Timber each one of them five foot long and about six inches thick square-wise Sharpen their ends and fix them so in the ground that they may stand Perpendicular and as near to South and North by a Magnetick Needle
Mistri◠Low who had a real and true Horn growing upon the right side of her Head three inches above her righ 〈◊〉 The length of it is eleven inches and two inches about The form is crooked spirally It is convex on the outer side and somewhat guttered in the inner side It is hard and solid and all very near of the same greatness It is not hollow within as horns are ordinarily but full yet it seems to be spongious as a Cane is It was seven years in growing and was cut off in May 1671 by Mr. Temple an expert Chirurgeon here at Edinburgh OBSERVATION XXII THis Observation is for finding the Primum vivens in Animals Albeit I doubt not but the red Spirit or Blood in most Terrestrial Animals is the first product of the Primigenial juice and therefore not improperly named the true Callidum Innatum of these Creatures by the Noble and Ingenious Harvey in his Book de Generatione Neither do I scruple to yeeld that the Heart and appendent Vessels are the first formed and perfected parts in the hotter kind of Animals yet I am confident to affirm that in many of the colder and moifter kinds of Aquaticks if not in all neither the redness and heat of the Vital Spirits nor the formation of the Heart Liver c. are previously requisite to the structure and existence of the other parts seing the light of life which at first inhabited the clear and Cristalin radical moisture before the formation of any particular part doth alwayes move in every living creature according to their particular exigency without any absolute dependency upon any one part or member excepting singular conditions wherein they may be stated as to its substance light and motion there being in some Animals a simple undulation in others a slow creeping but in the more perfect an impetuous running or rather flying of the Vital Spirits necessarily required for illumination and vivification of the whole For confirmation I shall give you this singular Experiment About the middle of March the sperm of Frogs according to the number of Prolifick Eggs therein contained sends forth a multitude of small round Creatures covered with a black and moveable Frock which about the end of March and beginning of April by the Gyrations of a Tail behind like a Rudder do slowly move their bodies in the Water At this time having opened severals of them I found nothing apparent to the naked eye but a clear thin Membran under the fore-named black Frock within which were contained a clear Water and some small Fibres like Intestines and in the fore-part a small orifice like a mouth About the middle of April its motion is more vigorous and the Tripes within are most evident lying in a very fine circular order but as yet there is no Vestige of Heart Blood or Liver c. About the middle of May the feet formed like small threeds appear thorow the black Coat within the Breast the Heart is then visible of a white and Fibrous substance the Liver is white and the Gall therein easily discerned But which is the head of this Experiment the Vital Spirit in form of a clear and pure Water is manifestly received by the Nervous Heart and by the contraction thereof transmitted to all the Body thorow white transparent Vessels which being full of this Liquor do represent the Lymphatick rather than the Sanguiferous Veins Last of all do the Pneumatick Vesicles which in this Amphibium supply the place of the Lungs arise in the Breast after whose production the Lympid and Crystalin Liquor while the Heart is turgid therewith seems to be red and fiery but in the other Vessels it is of a faint pale colour untill about or near the end of Iune the Frock being cast off and a perfect Frog formed the whole Vessels are full of Blood or a red substance very thin and clear the Liver and Pneumatick Vesicles c. become red and Rosy so that the Blood in this Amphibium which in the more perfect Animals is first compleat seems to be the last part in attaining its perfection That Salmonds and great Trouts have an aqueous liquor which runs thorow their Arteries and Veins before their Blood attain the true consistency and saturat tincture I am certain whether it hold in many others I suspect but dar not affirm Hence it may be if mens observations were frequent in all kind of Anatomical inspections in several Embryo's of every species it would be found evident that the Blood in all these called 〈◊〉 〈◊〉 〈◊〉 〈◊〉 〈◊〉 hath its immediat original from a simple homogeneous and uniform liquor and doth by gradual and frequent influences of the vital ferment of the heart receive at length the full tincture essence and subsistence requisite for vivification and illumination of the whole members Whether this Experiment doth not sufficiently impugn the universality of the hearts first living the original of the Gall from the fervour and ebullition of the Blood the production of the Blood by the Liver and many other ancient errors let any judge who will but take pains to make and compare Harveys trials de ov◠with this of the Porwigl or Gyrinus ab ovo Yea if the aqueous liquor be not one with the vital Spirit and subsequent Blood then my eyes and taste are altogether erroneous Moreover it were to be wished that Physitians would not simply stand upon the Galenick suppositions of the four alledged Components of the Blood nor any such or equivalent fancies of the latter Chymists but that they would seriously examine the first original and rise thereof from the Primigenial juice or liquamen the progress and perfection of its tinctures how many renovations or new tinctures it is capable of the vast difference between the Blood of old and young Animals though it may be they are both univocal substances while in their integrity within the Vessels with the specifick discriminations not only of that of any one Aquatick from any Volatil or Terrestrial but likewise of any one Species living in the same Element with these that enjoy the same Aliments but of a different Species And lastly the variety of particular constitutions and singular properties of individual Animals radicated in the fountain of life or first original of the Blood If these things and many more were truly inquired after though the Cook be sometimes necessitated to throw away some of the Broth with the Scum I doubt not but the Neoterick Invention of Transfusion of Blood would prove altogether ridiculous and the ancient mistake of too much Profusion of this treasure by Phlebotomy might suffer some reasonable checks from infallible Experience and sound reasons not here to be mentioned There are truths in Natural Philosophy which I doubt not but sound reason and experience will convince the vain world of in due time OBSERVATION XXIII THis Observation is concerning the aliment and growth of Plants The inquisitive wits of this and the last
age having rejected the old opinion of the earths nourishing of Plants or being converted into their aliment have made many laudable Experiments for finding out the materials and means of their growth and vegetation such as Sir Francis Bacon's Observe of Germination Helmonts of a Willow and the Noble Mr. Boyl's of a Gourd c. For though a Tree be cut down and the root thereof wax old in the earth and the stock die in the ground yet through the sent of Water it will bud as Iob speaketh Chap. 14. 7 8 9. I shall add a short remark of a Willow growing without earth Upon the 13 of April 1662 I set a top branch of the Peach-leaf'd Willow in a Glass-viol among 12 ounces of pure Spring Water with three small buds upon the top thereof scarce yet discernable The first ten or twelve dayes little white specks appeared upon the sides of the Willow like small drops of Quick-silver or like the first Bubbles that arise upon the fermentation of Ale or Wine but no consumption of the Water all this time Indeed the Gemms which stood three inches above the Water did visibly swell about the twelfth day About the fifteenth day I perceived small white roots within the Water upon several places of the Plant and observed the Liquor grow somewhat thick and decay in bulk considerably Having perceived this I took another Glass of the same bigness with that wherein the Willow grew and having filled both top-full with Spring Water I observed clearly the consumption of the Water wherein the Plant stood to be so great that during May Iune and a great part of Iuly every week at least an ounce and an half or two ounces of it were insensibly spent whereas the other Water standing by in an open Vessel of the same size made not waste of one spoonful in a whole moneth About the middle of August the Water turned very thick and green like that whereon Duck-weed useth to grow and the fair white roots were all obscured from the sight although the Vessel by the multitude of roots was not capable of the third part of Water it received at first At this time the branches were advanced to half the bigness and a much greater length than the whole stock at its first planting and the leaves of as fresh a verdure as any Willow in the fields Thus having observed that a tree of four ounces weight could in three moneths time and little more consume insensibly seven or eight times its own weight of pure Water without the warm preservation of the earth and by its own proper digestion to thicken the remnant of the Water that it might serve for lorication of the tender fibres of the roots I took the Glass the Tree and all and threw them over a Window supposing it needless to recruit the Water any more and judging it impossible without the warm guard of the earth that the naked Tree could be preserved in Winter yet it had the good fortune to fall among some thick Herbs in the corner of a little Garden where after it had lien all Winter it was found and brought back to me the branches fairly budding in April the whole Tree fresh and green yet very little Water was left in the Glass by reason as I judged it had fallen upon its side Then I endeavoured to keep Water about it but the Stock filling the neck of the Viol and the Roots the whole body thereof the starved Plant died in May after it had lived a whole year without earth From this it would seem that this kind of Tree and it may be many moe doth dissipat insensibly six times more Liquor than it doth assimilar and by consequence that a great quantity of moisture is necessary for maintainance of great Woods Neither is there any way so advantagious for draining moist ground where there are no living Springs as that of planting abundance of Timber which will best agree with that kind of soyl for by this means what was formerly noisome and superfluous is now converted partly into the useful aliment of the Timber and partly sent abroad in insensible exhalations which according to the nature of the emitting Plants prove either very noisome or wholsome to the Neighbour-Inhabitants Great care therefore would be had in the choise of such Trees as are to be planted in such moist ground as are near to mens dwellings or places of concurse They are not fools who prefer Firs and Lime-trees in their Avenues to Oak and Elme Let the effects of the Atomical exhalations of Alder and Oak upon fine Linnen and white Skins be more particularly noticed Having spoken somewhat of the aliment and growth of Plants I shall in the next place give a short hint at the motion of their aliment especially of Trees That the alimentary juice of Plants is much thinner than that of Animals no man I suppose will deny seing that is conveyed thorow the trunck or body of the Plants by inperceptible pores but this for the most part is sent thorow all the members through patent and manifest Vessels But how the nourishing and vital juice in Plants doth move and by what passages hath not yet been made known by any that I have seen I made once a few Observations for trying of the motion of the aliment of Trees which bred in me this conjecture The nutritive juice of Trees is transmitted both to the roots and branches through the heart or pitch and woody pores of the Timber and when it is come to the extream parts it returns again from the tops of the roots and branches between the bark and timber into these forenamed interior passages and so back to the extremities again and that continually so long as the life remains And because the substance of that skin or bark which invests the fibres of the root is more open and porous than that which is upon the outward branches therefore it seems that so much as is superadded to the stock of the former aliment from the earth is conveyed to the heart and pitch by means of and together with that part of the retrograd juice which returns from nourishing and enlivening the timber of the root-branches for it is an easie Experiment to make the top of any Tree become root by laying it down and receives the impressions of the life of the Tree common to the whole mass of alimentary juice like the I hyll in Animals mixed with the blood of the Veni-cave before it come to the heart This motion is not to be thought alwayes alike swift or of equal celerity for the vital juice of the Tree becomes so thick and oleagenous in the Winter that the motion thereof to the outward is scarce discernable though the preparation of the Gemmes both for leaves and flowers are observed by the curious and can be distinguished even in the coldest seasons and the returns inward are in so small quantities that they are rather like
where four Mills goes with the Water that comes from under ground out of the Coal which kind of Levels are only found where the Coal lyes in a Field which hath a considerable Rise or ascent above ground there being a necessity to make use of the other two wayes spoken of for drying the Coal when the Field in which it lyes is a Plain Further of these Coals which are dryed by the Free-level for so they term the Level that runs unforced there are some to which this kind of Damp is more incident than to others The cause of which difference is found to be the solidity and clossness of the Metals whether of Coal or Stone wherein some exceeds another There being some that are full of rifts or empty spaces I mean empty of any part of the same body where they are which will sometimes serve to convey a considerable quantity of Water in place of an aquae-duct or level which spaces are termed by the vulgar Cutters which sometimeâ— proves very profitable in the ground where they are found both in regard of the use they serve for in stead of Level and for rendring the Metals wherein they are found more easie to work in making them yeeld easily to the force of the wedge and leaver Other Metals there are wherein few of these Cutters are to be found and if water be to be conveyed through them there is a necessity of cutting a passage through them for that effect Now this Damp whereof we speak is found most frequently and most violent in the first sort of Metals viz. in these which are full of Cutters or Rifts which gives some ground to this conjecture of its cause These Spaces which are found in Coal or other Metals as Stone or Till before the Coal begin to be dryed by a Level are full of water which is still in motion as are all subterraneous springs whereof some are more violent some more slow conform to the passage they have to the fountains above ground where they discharge themselves Now for drying these Coals and rendring them workable there is a necessity to cut a passage thorow which that water discharges it self quickly it being large and admitting a great quantity at once by vertue whereof a great field is drained at once and the Sourse not being able to furnish so much water as the Conduit is able to convey these Spaces in the body of the Metals being emptied of Water must needs be filled with Air which Air having little contact and commerce with the great body of Air above ground and so hath little or â—o motion corrupts in these places and thereby becomes poisonable so that when any Animal is necessitat to draw it and respire by it it choaks them on a sudden just as standing Water which being without motion corrupts and becomes poisonable though haply not in so great a degree as the Air the Air being a body much â—iner and purer than Water that holding good in it corruptio optimi pessima This is much confirmed by what is before asserted that in the Coals whence the Water is drawn and they drained but not by free-course but by Force as Pumping and drawing by buckets these Damps are seldom or never found because the passage of the Water being forced it does not so suddenly dry the Metals as the other whereby there is alwayes left in these Spaces some Water which being it self in motion keeps the Air also in motion with it and thereby the Air is kept from corruption at least in such a degree as it is in the other Hence we find that in these kinds of Coals the Rooms under-ground are alwayes wet or for the most part they are so whereas in the other there will be no Water found to wash a mans hands and sometimes the Coal through want of Water becomes so dry that it cannot be wrought in great pieces as others but crushes in the very working and when wrought is rendered useless and will not at all burn This puts me in mind of a very pleasant conception of a worthy and learned Person Doctor George Hepburn of Monk-ridge with whom I had occasion one day to discourse on this Subject He is of opinion that the Water is the Mother of the Coal whereby it is preserved fresh and incorrupted and that when the Water is drawn off and this Damp follows it is not the Air which succeeds in place of the Water and is corrupted for want of motion that occasions it But as we see when the corruption of a Liquor within a Vessel when the Mother is gone corrupts the Vessel it self and occasions an ill savour or taste in the Vessel so that the Coal being corrupted by the want of its Mother the Water corrupts the Air in the subterraneous Spaces as in Coal-Mines Sinks Caves and other such like He had likewise another pleasant conception about the generation of Coal judging it to be formed gradually out of another Metal as of Till by the help of Water of which he himself may perhaps give an account And though I be not of his opinion in that matter yet I must acknowledge I was taken with it and shall be glad to see a more full account of it from him than he had access to do in the short conference we had The effects of this Damp are first it hinders the burning of all combustible matter as Candle Coal Pitch Sulphur c. so that if you take a Torch lighted and let it down to a Sink where the Ill Air is prevalent in the time it shall straightway extinguish it Or take a Coal which is burning and let it down it shall not only extinguish the Flame but shall make the Coal in an instant dead and as cold as never heat had been in it But the most dangerous effect is its killing of living Creatures whereby many persons have been suddenly killed Some in going down to a Sink where it hath been powerful have fallen out of the Rope and perished Others have been choaked and yet have gotten out by the help of others in a sudden and have remained a considerable time without the least appearance of life but yet have at last recovered Yet it hath been observed that some of these persons that have been so struck with the Damp and recovered have had alwayes some lightness of Brain thereafter and never so settled as formerly This I know to have happened to one whom I have seen so many times thereafter What hath been its effects on some Animals whereof you have made Experiment I leave to the account you have given One thing I shall only mention which to me seems somewhat strange that notwithstanding these Damps are so effectual and causeth so suddenly the death of Animals yet the Ratts which are in some of these places where the Damps are most violent are not reached by them For sometimes when they are so powerful that nothing that lives can enter under ground
without sudden death yet they continue there and are not found to diminish even where they have no access to escape by coming above ground Or if it should be imagined they removed to some other place of the ground where the Damp is not how is it they are not as quickly choaked with it as Dogs are and other Animals which at the first encounter are killed If it be inquired how comes it to pass that in these Fields of Coals which are dryed fully as was said and to which these Damps are incident because of corrupted Air that remains within the Body of the Coal or other Metals how comes it to pass I say that they are but sometimes incident and are not alwayes found For clearing this it is certain that even in the grounds where these Damps are most frequent for the reasons above-mentioned yet they are only powerful when the Wind blows from such a certain Point as some Chimneys that do only smoke when the Wind is in such an Airth This is so generally and well known that the Work-men observe it and when they find the Wind in such a Point whence they fear the Damp they will not enter under ground till trial be made of the Air which they do in Sinks by first letting down a lighted Candle or some burning Coals which if they do not burn then there is no access to enter Secondly the wind in which this Ill Air is most noxious and hurtful blows from that Point where the Field of Coal lyes that 's not yet wrought which seems somewhat strange and yet when duely considered it will appear abundantly consonant to reason An example of this is to be found in the Coal of Tranent and Elphingston the Streek whereof goes to the rise of the Hill above ground from N E to S W as hath been formerly observed So that the beginning of their Level is at the N E point of the Streek from which the Coal hath been wrought up along the Streek towards the S W the Wastes lying all towards the N E. Yet when the Wind blows from N E or N or almost from any other Point of the Compass they are not troubled with this Damp. But if it blow from S W and blow hard they are in hazard to encounter it And though the Damp is not alwayes found when that Wind blows whereof there may be some particular cause yet it is never observed in another Wind whether it blow less or moâ—e the reason whereof may probably be that the Wind blowing from other Points as from N or N E hath more access to enter the Wastes under ground and move the Air that is in them towards the face of the unwrought Coal whence is supposed to proceed the corrupted Air that lurks in the Rifts and Cutters thereof from which the Water is drawn away and occasions the Damp Now this Air being moved by the force of the Wind keeps the corrupt Air from coming out it being stronger then the other Whereas upon the contrary while the Wind blows from S W it entering the empty Rooms drives the Air under ground from the face of the unwrought Coal down towards the old wastes which have their course from the beginning of the Level By which means the Air that is corrupted within the bowels to speak so of the Coal comes out to the Wastes without resistance it being certain that Fluid Bodies as Water and Air inclines to move towards that place where they meet with the least resistance Hence is it that the more direct the Wind be in blowing against the â—ace of the unwrought Coal as is the Wind from N E the Ill Air is the more repelled and driven back but the more oblique it be as are the Winds from these Points that are nearest to S W the Air is not so good and free which difference is known by the burning of Candles they burning with greater difficulty in these Winds than in others which blow from these Points nearest to N and N E. Some are of opinion this Ill Air in those places we have been speaking of comes from the great Wastes that ly above the un-wrought Coal and by strong S W Winds is driven thorow the Cutters thereof Or the Wind blowing from that Point and coming thorow these Cutters brings the corrupted Air alongs with it even as after a showr of Rain a spait of Water comes and carries alongs with it both the foul Water and the clean it meets with Though this may be probable which seems to be your own opinion yet the other seems to be more probable The other sort of Damp is that which they call want of Air and though the term be not altogether proper there being no space without some Air yet there is a want of Air which is sufficient for respiration of Animals or for the burning of fire This is ordinarily â—ound in the vunning of Mines under ground for coâ—veying of Water from Coal or other Metals or in the waste Rooâ—s of Coals where the Sinks are very deep and to evite the charge thereof there is some necessity to work as far under ground for winning of Coal as is possible without new Sinks The cause seems to be that the Air under ground in such cases wants communication with the Air above ground because it is found that by giving more communication the evil is cured Whence comes the necessity of Air-holes in Levels which are so many Sinks set down for no other use but for giving Air to the Workers Some are of opinion that this defect might be supplied by the blowing of Bellows from above ground through a Stroop of Leather or of some other thing which must run along to the end of the Level for keeping the Air thereâ—in motion But I have not yet heard that it hath been made practicable The effects of this Damp are not so dangerous as these of the other 'T is true it will kill Animals and extinguish burning Coals and Candles but not so suddenly as the former and so people are not so readily surprized by it The other seems to kill by some poisonous quality in this Animals dies for want of sufficient Air for respiration Therefore in advancing in a Coal Room or Level where this is you shall see the flame of the Candle grow less and less by degrees till at last it be totally extinguished and the person entering shall find the difficulty of breathing grow greater as he advanceth forward till at last he cannot breath at all Hence it is that few or none are killed by this kind of Damp and all its prejudice is that it renders the work more chargeable when there is a necessity to remove it For that which they call Wild-fire it being a thing not incident but to very few Coals is less known than any of the rest of the accidents that follows Coals The account I have heard of it is that in some Coals which naturally are
Crops of the Metals the body whereof lies in it whether of Coal or Stone in that case there is no way to try but by sinking or boaring The way of ranging is conspicuous in the following figure Figure 11. The piece of ground to be tried is P N where there are several Seams of Metals that Cropps out at the Points K L M N. Suppose the lowest to be the Coal viz. I N for which you are to make trial You Digg first at K without the Cropp of the Seam F K and you dig till you find the other Seam of Stone G L at the Point C. Following the Rule before given you advance before its cropp and diggs at L and finds the other Seam of Stone H M at the point D from which you also advance and diggs before its cropp at the point M and finds your Coal at the point E. But if by advancing over the cropps of these Metals which comes out from under one another you find no Coal then you are to range backward for the cropps of Metals lying above these where haply the Coal may be as at O and P. This in my opinion is the most certain and exact way of trying Fields for Coal or any other Metal of that nature and least chargeable of all others The second of this last part I promised to speak of was in order to Levels or Coal-Mines which are nothing else but Conduits or Gutters made under ground for conveying of the Water from the Coal and so rendering it workable It seems that a very little time before this that way of Mineing under ground hath not been fallen upon For there are to be found Coals wasted in their Cropps only for conveying the Water whereof they have made a Conduit or Level which hath been open to the Surface like a great Ditch some whereof have been ten or twelve fathom in their deepness The beginning of the Level to keep the term used must alwayes be at the lowest part of the Field where the Coal lyes to be dryed Some whereof by the rising of the ground and the Streek of the Coal rising that way as we shew before gives the advantage of a Free Level that is when the Water comes above ground of its own accord without being forced by drawing In others there is a necessity of Engines to draw the Water from the lowest part of the Level and bring it above ground which Engines are of several sorts As when men drew with ordinary Buckets or when there is a horse-work or water-work and that either by a Chain with Plates and a Pump or with a Chain and Buckets all which are very common especially those we have in Scotland they being capable to draw but a very small draught making only use of one Sink for that effect But there are to be seen in the North of England in Bishoprick Water-works by which Water is drawn above 40 fathom in perpendicular but not all in one Sink The manner whereof is thus there being a Sink from the end of their Level to the surface of the earth where their Works are going 40 fathom deep which must dry the Coal-Sinks at 60 or 70 which ly above the Banks of the River where the Water-works are scituated there is first one 40 fathom deep from the Grass Another in a right Line from that of 24. Another of 12 upon all which there are Water-works In the first Sink the Water is drawn from the bottom 12 fathom and thence conveyed into a Level or Mine which carries it away to the second Sink By the second â—ork the Water is drawn out of the second Sink 14 fathom from the bottom and set in by a Level to the third Sink which being only 12 fathom deep the Water-work sets it above ground The form of the Engine is after this manner In the first Sink there is an Outter-wheel moved as other Milns are by the Water of the River upon the end of the Axle-tree of which Wheel there is a Ragg-wheel turning vertically as doth the Outer-wheel This Ragg-wheel by a Nutt or Trinle turns another which moves horizontally the Axle-tree whereof goes right down in the Sink and may be is 8 or 10 fathom at the end whereof there is another Ragg which by a Nutt turns another Wheel which goes vertically as the first Ragg and causeth another Wheel with a long Axle-tree turn as the first and so down till it come to the Wheel which turns the Axle-tree by which the Chain is drawn The second Sink hath such another Engine but not so many Wheels in regard it is not so deep The third hath only one single Wheel whereby the Water is drawn above ground The most curious of these Engines that are to be seen are at Ravensworth near to Newcastle which belongs to Sir Thomas Liddel a most ingenious Gentleman who for procuring a Fall of Water which may serve the Wheels of all the three Sinks hath erected the first work upon Pillars like a Wind-Mill pretty high above ground from which the Water falling makes the second go closs above ground And to make the Water fall to the third the whole Wheel is made go within the surface of the ground which terminats at a River under the Works which Mine is of a considerable length Where Water cannot be had to make such Works go they use Horse-works but not wâ—th so good success being more chargeable and not having so much force and power as the Water-works But I am of opinion that Wind-works might serve well where Water cannot be had and when no Wind should happen to blow the same Works might be supplied by Horse and that the Wind when it blows but ordinarily hath as much force as so much Water which is made use of for turning such Wheels is to me unquestionable For I have seen in Holland a Wind-Mill that by the motion of the Outter-wheel caused seven pair of Mill-stones to go at once besides another motion for bringing the Victual from the ground four or five Stories high to be Grund And several Saw-Mills which besides six or seven great Saws they caused go did by another motion bring up from the Water great Trees like Ship-Masts to be fawen and placed them right against the Saw all which could not be but of greater weight than 10 or 12 fathom of Chain with Buckets or Plates for drawing of Water But to return for the right making of a Level the true hight of the ground where the Coal lyes must be first taken that it may be known how much of the field can be drained by it which must be done either with a Quadrant or with an Instrument made express Then care must be taken to take the lowest part for the mouth of the Level that the field can afford and from that it must be carried in a straight line towards that part of the field where the Coal is thought to be encountered by the Mine In working