Atmosphere resting upon the surface of Water AB 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 GF that not only presseth down the Water FD 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 GF 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
they do not counter poise 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 by 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 IKLM as it is prest down by the water EFGH 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 I. 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 EFGH 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 other Liquid also THEOREM VIII The Pressure of Fluids seem to be according to Arithmetical Progression Figure I. 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 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 force 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
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 HI to AB and so the Cylinders AC and BD being higher press with greater weight upon the bottom CD 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 MPVX and fill it with VVater to QR Next take a large bladder WY 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 QR to MP 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 WY makes the water swell from QR to MP by which means the Pillars of Water MV and PX becomes higher and so presseth with greater weight upon the bottom VX 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 QR to MP 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 MV and PX 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 ABCD 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 AB by which means the Pillars AC and BD 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 STVX 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 MP by taking out the bladder settle down to QR 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 FG. 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
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 fiâ—st 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 LIH 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 IH falls down by degrees but in effect is really thrust out by the strong Bensil of the comprest Air IL 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 GK 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 KG 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 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 peices 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
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 Bensil 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 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
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 not only the whole Brandy in the Pipe subsided and was mingled with the stagnant Brandy but at this exsuction there came a great quantity of Air from the mouth of the Pipe and rose up thorow the stagnant Liquor in Bubbles Having made another exsuction there came yet more Air out and so copiously that I thought there had been some seak in the Tub through which the outward Air had entered but knowing the contrary I continued Pumping a very long time till I found less and less come out and at length after near 30 exsuctions it ceased This Air to appearance was so much as might have filled twenty Tubs every
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 sound 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 no 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 finer 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 straight 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
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 draw 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 Work 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 with 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 sawen 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 whereof two things are in a special manner to be reguarded First that the Level be wrought without ascent or descent the best way for trying this being by the surface of the Water passing through it which ought to be as little moving as can be for the loss of one foot of Level which the ground gives is a loss of a considerable parcel of Coal to be digged especially if it be state If there occur any Metals which are impregnable in the course of the Level so that it is impossible to follow so straight a line in regard the Mine must be wrought over the top of that stone which is unworkable in that case there is but one of two to serve the loss of Level either the Coal rises in Streek towards which the Mine is carried and if that be then after that stone is past the Level must be carried as low as it was before it encountered the same and the course of the Water shall not be obstructed because the sourse viz. the Coal from whence the Water comes rising higher than the Stone the Water shall easily pass over that hight Hence it is that we see in some Coals that have been wrought at the lowest point of their Streek by a drawing-sink and the Streek rising from that point the Water that hath come off the Coal being in its Sourse higher than the mouth of that drawing-sink hath made it to over-run and serve to discharge all the Water that comes therefrom But if the Mine be run to a Coal that after it hath overtaken it rises no higher in Streek than the Mine it self the Water that comes from it will not pass over any hight in its way but will be unquestionably stopped Therefore in case such an impediment could not be removed as many times such Metals will fall in which are unworkable in a direct line the use of a Siphon might be tried which would unquestionably supply the loss of about 32 foot of Level this being the hight in Perpendicular to which the Pressure of the Air is able to raise Water up thorow a Siphon The next thing to be observed in carrying on of Levels are the Air-holes for which there is a necessity indispensable In setting down whereof care must be had that they be not directly upon the Mine lest rubbish falling thorow from above ground should stop and obstruct the same and so obstruct the course of the Water and therefore it 's better they be set down at a side their only use being to communicate fresh Air to the Work-men which if it could be otherwise supplied as I think it not utterly impossible would render the charge of the Coal-works a great deal more easy Other things might be spoken to of Levels as that some run with the course of Metals they pass thorow and that some run against that course and of bringing Level from the Dip of an upper-Coal which hath a Level of its own to dry a Coal lying under it which cannot be otherwise done But these things being common and obvious to any who have but the smallest skill and experience I shall forbear This confused account your importunity hath drawen from me for which if your Book suffer censure which I grant it may do as to this part of it you are to blame your self and so I rest and am c. FINIS
by the least conceivable Power as the Earth by the force of a mans hand But how is it possible to contrive Artificially an Engine for that purpose which will do that by Art which the demonstration makes evident by reason It was thought a great enterprize when Pope Sixtus the fifth transported an Obelisk which had been long since dedicated to the memory of Iulius Cesar from the left side of the Vatican to a more eminent place 100 foot distant but to raise a Ship of 1000 Tun intirely nay a weight 100 times greater is surely a far greater enterprize This Invention is so much the more admirable that not only by it any supposed weight may be lifted but from any deepness Though this perhaps cannot be done Mechanically because of some Physical or Moral impediment yet according to the Laws of the Hydrostaticks it can be demonstrat and made evident by reason And if this be then surely when the Weight is determinat as the burdens of all Ships are and the deepness known to be within so many fathoms this Invention cannot but be successful Though the strength of Mechanical Inventions may be multiplied beyond the bounds of our Imagination whereby the greatest Weight may be moved by the least Power yet the Wisdom of God hath thought it fit so to confine that knowledge that it cannot teach how both of them can move with the same quickness and speed For if that were the very works of Nature might be overturned Therefore it is observable that when a great Weight is moved by a small Power the motion of the one is as much slower than the motion of the other as the Weight of the one exceeds the Force of the other If it were possible Mechanically to move the Earth with the Force of a mans hand the motion thereof would be as much slower than the motion of the hand as the Weight of the one exceeds the Force of the other which is a great disadvantage And as the Weight and Power do thus differ as to swiftness and slowness in motion so also as to Space For by how much the Power is in it self less than the Weight by so much will the bounds or Space the Weight moves thorow be less than the Space the Power goes thorow If it were possible keeping the same instance to move the Earth with a mans hand the Space thorow which it passeth would differ as much from the Space the hand goes thorow as the one exceeds the other which is another disadvantage It may be thought that if this Invention depend upon Mechanical Principles it may be obnoxious to these abatements I answer though there be in it a Pondus and a Potentia a Weight and a Power this moving the other yet it will evidently appear from Experience that the motion of the one is as swift as the motion of the other and that the one moves as much Space and bounds in the same time as the other which is a great advantage In this it excells all the Mechanical Powers and Faculties that have ever yet been invented and practised If any think that such a device cannot be effectuat without a considerable expence I answer the expence is so small that I am ashamed to mention it The method and manner of doing this is most easie likewise Neither ought this to be a ground why any man should contemn it since the most useful Inventions ordinarily are performed with the greatest facility As it commends this part of Philosophy to all ingenious Spirits as most pleasant and most profitable so it gives a check to the ignorant who look upon it as a Science long ago perfected In praise of the AUTHOR and his WORK 1. WHilst Infant-Art no further did pretend Then to flat notions and a bare desiâ—e What by small toyl we now do comprehend Our Predecessors only did admire 2. Now fruitful Reason arm'd with powerful Art Uncovers Nature to each knowing eye Our Author to the World doth here impart What was before esteem'd a mystery 3. The various motions of that Element Whose liquid form gives birth to much debate By demonstration he doth represent Unfolding th'intrigues of that subtil state 4. The Waters Course and Sourse from whence they flow By him to th'sense so clearly are display'd Their current Weight and Measure now we know 'T is no more secret but 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 ABCD there is a second EFGH and a third IKLM 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 AEINOPQ the other BFKRT 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 Siphon 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
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 Cylinder 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 BCD descend As this Proposition is true in order to the first and visible surface ABCD so it is true in order to the imaginary surface IKLM 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 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 in 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 surface 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 ABCD 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 ABCD. 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 ABCD. 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 ABCD 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 also for if a Cube of Timber resting in the space T be just the weight of the Water T the imaginary surface OTV 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
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 EFGH 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 OTVX 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 ABCD 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 Phoenomenon 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 that pressing Fluid Figure 2. FOr understanding this Proposition let us imagine GHCD to be a Vessel in whose bottom there are five inches of Mercury EFCD Next that above the stagnant Mercury there are thirty four foot of Water resting namely ABEF Lastly that upon the surface of the said Water there is resting the Element of Air GHAB whose top GH I reckon to be about six thousand fathom above AB Besides these let us imagine that there are here three Pipes open at both ends the first whereof CAG having it 's lower orifice C drowned among the stagnant Mercury EFCD goeth so high that the upper orifice goeth above the top of the Air GH The second whose lower orifice I is only drowned among the Water ABEF reaches to the top of the Air likewise The third whose open end K is above the surface of the VVater ANB 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 EFCD cannot press it self within the Pipe CG higher then E. Neither can the VVater ABEF press it self higher within the Pipe IL then the point N. Lastly neither can the Air GHAB press it self within the Pipe KM higher then M But when one Fluid presseth upon another as the VVater ABEF upon the Mercury EFCD 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 ABEF can raise the Mercury which altitude is twenty nine inches above the surface EIF But if a second Fluid be super-added as the whole Air GHAB 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 IL namely from N to R. Now I say the outmost and highest point to which the Element of Air GHAB can raise the Mercury is from O to P for by the Pressure of the Water ABEF 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 EO is twenty nine inches because the deepness of the pressing water ABEF is thirty four foot And the hight of the VVater NR is thirty four foot because the hight of the Air GH above AB is six thousand fathom or thereabout And for the same reason is the Mercury OP twenty nine inches THEOREM XXVII 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 GHAB twenty nine inches of Mercury OP are supported as well as the twenty nine inches EO by the Pressure of the VVater ABEF So doth the same Air sustain the thirty four foot of VVater NR which are really as heavy as the twenty nine inches of Mercury OP 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 clear from this same Figure where by the Pressure of the Water ABEF twenty nine inches of Mercury EO are suspended as truly as the Mercury CE 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 NR 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 EO Lastly that as much Air as will fill the Pipe between O and G is just the weight of the Mercury OP 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 EFGH 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
of Water LK is equally and uniformly prest for with what weight the outward Water ML and HK 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 ML and HK 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 LK 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 ML and HK press the imaginary surface LK 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 MGH 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 HK within the Pipe and the outward Water that sustains it I means 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 EGI 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 NQ 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 XS 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 ML ought to sustain the inward GI but cannot see why the outward Air TZS and VRX ought to sustain the inward Mercury RX 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 TZS and VRX 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 RX and ZS 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 end 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 Torricellian 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 rest upon the surface MH 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 EG 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 MGH The same Phenomenon happens in taking the Air out of the narrow Pipe FK 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 MH 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 MH 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 MH 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 DEHK The second that 's imaginary is LI six foot below it The third of the same kind is MG six foot lower The fourth is NFO six foot yet lower The last and lowest is ABC There are here also four Tubs or rather one Tub under four divers positions with both ends open After this Tub DA 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 EF and then you shall see as the
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 farder 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 other 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 strictâ—y 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 GH that 's raised by the surface of Air FG 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 FG. 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 FG 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 raising 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 FG 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 suâ—face hath lost all its Power and Pressure which is also evident in the Pillar For understanding this let us suppose ACB 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 EB on which it rests as was between the surface FG and the pondus of Mercury HG For as FG had 29 degrees of power to raise GH so the Pillar AB has 29 ounce of weight to overcome the surface EB And as the surface FG became one degree weaker by raising one inch of the Mercury HG 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 FG hath lost all its Pressure by raising the Mercury from G to H and if the Pillar CB 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 bâ—ought to an equipondium there is no Pressure in them at all For answer consider first that in all counterpoises there aâ—e 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 pondus 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 FG 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 FG still remains of the same force and power while it suspends the Mercury GH that it was of before Likewise the Pillar AB cannot be said to have lost all its pressure absolutely by falling down from A to C but only respectively because the said Pillar CB 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 pressing 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 ABCD and fill it with Water as high as HI Take next a Cylinder of stone FG and drowning the half of it among the Water suspend it with a chord to the beam NO 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 fiâ—st the weight of the Water before the stone be drowned 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 KL 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 in stead 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 HI to AB the VVater of the Vessel would become
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 FG 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 MN where I suppose is standing the Vessel ABDE with stagnant Mercury and drown the end below the surface AB This being done the Mercury falls from the upper end H to the point G and there halts the space HG 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 DCE For while the Tub is compleatly full the weight is so great that the surface DCE 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 AB 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 LIK 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 MN 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 LIK 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 AB 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 DCE 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 DCE is of the same strength with the weight of the Pillar GFB And this lets us see the reason why the whole 70 inches cannot be suspended for if the outward Pressure that 's upon AB be but equivalent to the Pressure of 58 it can never make the surface DCE 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 FB 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 AB 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. 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 DCE 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 AB 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 GF 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 FB 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 poised 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 DCE 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 sort of vacuity 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 IH 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 IH that rests upon on 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 IH 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 IH being of the same weight with the Mercury GF and the foresaid Pillar of Air being of the same weight with the Mercury FB 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 IH that 's 34 foot high and of the same thickness with the 29 inches of Mercury GF 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 SI that rests upon the top of the Pillar of VVater IH of the same weight with the 29 inches of Mercury FB 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 IH 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 EAFCGD must be far heavier than the 58 inches of Mercury HB 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 EAFCGD is not found while a man poises the Tub between his fingers but only the weight of the part GA which is exactly the weight of the Mercury HB But here occurrs the great question namely why I find only the weight of the Water GA and nothing of the weight
of the Water CE or DE I answer I cannot find the Pressure of the Water CE because it is counterpoised with the upward Pressure of the Water IK And for the same reason I cannot find the weight of the Water DF because it is counterpoised by LM but because there is nothing between H and A to counterpoise the downward Pressure of the Water GA therefore I find that If it be objected that the Water IK cannot counterpoise the Water CE because the one is farder down than the other and consequently under a greater Pressure than the other I answer though IK be stronger than CE yet a compensation is made by the weight of the Tub. For understanding this let us suppose the Water CE and DF to press downward with the weight of six pound and the Water KI and LM 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 IL. And if this be then must the Water IK and LM be four pound weaker with the Tub than without it and must only have six pound of upward Pressure Fig. 9 Pag. 5â— Fig. 10 Fig. 1â— Pag. 7â— Fig. 13 Pag. 81 Fig. 14 Pag. 86 EXPERIMENT XI Figure 15. AMZC is a Water 15 foot deep AB a Glass-tub 14 inches long and full of Mercury BC 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. DE is a Tub full of Mercury 28 inches long with a Pillar of Water above it EF 12 foot and eight inches GH a Tub 42 inches long with a Pillar of Water above it HI 11 foot and six inches high And lastly ADGSM 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 AB to weigh 14 ounce and the 28 inches of Mercury DE to weigh 28 ounce the 42 inches GH 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 DE 28 ounces will be required in the Scale L and 42 if you weigh the Tub and Mercury GH 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 GH 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 HG 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 AB 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 BC that does this Neither doth the weight of the 28 ounces of Mercury DE burden the Ballance but only 28 ounces of the Water EF. Neither doth the Ballance support the weight of the 42 ounces of Mercury GH but it is only burdened with 42 ounces of the Water HI The reason is most evident because according to the Principles of the Hydrostaticks already laid down the Cylinder of Mercury AB within the Tub AB rests immediatly upon the imaginary surface of the Water ADG 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 BC and 28 of the Water EF and 42 of the Water HI To make this seem probable consider first as was noted that this VVater is 15 foot deep and consequently the Pillar of VVater BC 13 foot 10 inches The VVater EF 12 foot eight inches And HI 11 foot and a half Consider secondly though this be true yet we must count the Pillar of VVater ZM 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 BC is 47 foot ten inches the Water EF 46 foot eight inches And lastly the Water HI 45 foot six inches Thirdly for easie counting I must suppose the whole Cylinder ZM to weigh 42 ounces every 14 inches one ounce and consequently the Water BC to weigh 41 ounces the Water EF to weigh 40 ounces the Water HI 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 BC being the pondus and the Mercury AB 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 found 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 counterballance the opposite Pressure and the more it is burdened it is the less able Consider seventhly that the Mercury AB which is evident in all Fluids not only presseth downward and burdens the surface ADG but also presseth upward and therefore actually endeavours to thrust up the Tub and so it is that the Tub is pressed between two namely between the Water CB and the Mercury within it Now from these considerations I say the scale K must support and bear up 14 ounce of the Water BC 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 BC 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 BC must press it down with 14 ounce only and so the Cylinder BC 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 AB 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 EF Imagine the second Tub to be suspended as the first seing the Cylinder of Mercury DE 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 AB press up with 27 ounce and the Mercury DE 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 AB being shorter and lighter than DE the surface of Water must press it up with greater force so that if the said surface AM be able to press up the Mercury AB with 27 ounce it must press up the Mercury DE only with 12 ounce According to this rule if the Mercury AB 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 AB 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 AB 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 BC that weighs so much does now really counterpoise it Let us imagine next these 14 inches of Mercury to rise and fill the Tub AB 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 HI 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 HI 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 DGS 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 DGS is able to bear it cannot impress any impulse therewith upon the top of the Tub within but easily can the Cylinder DE impress an impulse and more easily the Cylinder AB seing they are lighter and so more powerful To evidence this a little more let us imagine two things first the Tub GH 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 IH 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 AB 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 AB but 14 ounce of the Pillar of Water BC. Secondly there 's here a clear ground for asserting a pondus and a potentia in Fluids because this Tub AB is prest down with the VVater BC 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 BC 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 GH with the weight of the Water HI 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 BC than the just weight of the Mercury AB 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 GH that wants all upward Pressure now would press up the Tub with 40 ounce the Mercury DE with 55 and the Mercury AB 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 AB than in DE. We see eighthly that the strength decayes and grows according to Arithmetical progression as 1 2 3 4 because if you make the Cylinder GH 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 DE 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 AB 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 GH and the outward Water that 's 49 foot deep But 't is not so between the said Water and the Mercury DE because the said Water is able to raise the said Mercury 14 inches higher therefore the Water only sustains the Mercury DE but counterballances the Mercury GH We see tenthly that the pondus of the pillar of Water BC 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 AB 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 AB 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 BC 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 HI found in the Ballance it takes 42 ounce to counterpoise it than of the VVater EF which is counterpoised with 28 ounce and the reason is because the top of the Tub H supports the whole 39 ounce of VVater HI the Mercury within the Tub not being able in the least to counterpoise it or thrust it up But because the Tub DE is more equally pressed the VVater EF presseth down with 40 and the Mercury DE presseth up with 12 therefore less weight of the VVater EF burdens the Ballance only 28 ounce Hence it is that because the Tub AB is more equally pressed than either DE or GH there 's less of the weight of the VVater BC 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 GH would fall down to about 13 inches Secondly the 28 inches of Mercury DE would fall down to as many And lastly the 14 AB 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 ZM 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 BC. The reason is because the Water BC is but of 14 ounce and the Mercury AB 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 EF seing EF is but 13 ounce Thirdly the same weight one ounce being deduced would counterpoise the Water HI because in this case it weighs but 12 ounce To proceed a little further imagine the Pipe GH to be suspended by the ballance as the Pipe AB 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 GSM 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 QR 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 QR 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 RQ 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 QO above
it it is 29 therefore being shorter the surface GSM 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 PS and the 28 inches of Water POQ being a far lighter burden by 26 than the 4â— inches of Mercury the surface GSM must be far abler to press them up now than before and therefore must diminish as much of the downward Pressure of the VVater QR 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 RQ that weighs 39. Lastly let in so much VVater as will depress the last 14 inches PS 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 GSM being liberated of the burden of Mercury and sustaining only the VVater within the Tub instead of it this surface presseth up the VVater within the Tub and consequently the top of it with as great force and wâ—ight as the top of the Tub without is depressed with the outward VVater RQ therefore 39 ounce depressing the Tub and 39 ounce pressing it up the Ballance must be freed of the whole weight of VVater RQ If it be objected that the 42 inches of VVater QS 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 RQ presseth down For answer consider that the part S is able to support 42 ounce of VVater and next that the VVater RQ 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 RQ If it be inquired whether or not would the 14 inches of Mercury AB 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 equilibrio with the Pressure of the ambient Water as the Mercury GH 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 comes 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 BC 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 GH 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 IH 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 GH 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 SQ suffers by the ingress of the VVater QO it s made up again by the same VVater If it be objected that the 14 inches of VVater QO 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 QO 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 a 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 Mercury subsides We see seventhly that 't is impossible for two 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 QS and the part of the surface S by the ingress of the Water QO 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 RQ after the ingress of the Water QOP than after the ingress of the Water QO We see ninthly that when a Body is equally and uniformly pressed 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 RQ 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 RQ We see
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 slowlier 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 slowlier 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 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 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 CD 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 CD were of Gold it would go further down than being of Brass or Iron and if CD 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 CD 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 ANB 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 easily suspended as
a thinner is this because if a Pillar of Mercury be thicker and consequently heavier than iâ— takes a broader and consequently a stronger surface of Air to â—est 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 weakeâ— 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 the 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 six inches thick But this seems rather to slow 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 AB and CD 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 IKPQ that 's 34 foot deep and suspended by a beam or long tree TV existing in the Air near the top of the VVater by a chord SE 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 CDNO This done I affirm that the beam TV neither sustains the under plain Body CDNOGH nor the 350 pound weight of Lead R that hangs down from the handle GH If it be objected that the beam supports the upper plain Body ABLMFE therefore it must bear the weight also of the under plain CDNOGH 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 of the lower VVater PQNO 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 IKLM 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 PQNO 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 IKLM 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 LM I suppose secondly that the lower Water PQNO 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 IK which is as much it may be truly said to weigh 400. These things being premitted
edge B is only burdened with 50 therefore 50 ought to yeeld to 400. I answer according to the 29 Theorem namely that a thicker Pillar of a Fluid is not able to press or move a slenderer unless there be an unequal Pressure therefore the thick Pillar that presseth the face cannot move the slender Pillar that presseth the edge but there is here no unequal Pressure seing the Water XYZV is of the same hight with the four Pillars that rests upon the face of the Butter I grant if the said Water were not so high as the other is by the one half then surely the Butter would be squeezed out at B because the shorter a Pillar be the less Pressure is in the surface under it therefore there must be less Pressure according to that supposition in the Water BC then now is Or put the case the Pillar IK were shorter then GH or LM the same effect would follow namely a squeezing out of the Butter from K. Or let us suppose the Pillar IK to be higher than GH or LM In such a case the weight of the said Pillar would press through the Butter From what is said we shall only inferr 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 Fig. 12 Pag. 81 Fig. 15 Pag. 100 Fig. 16 Pag. 109 Fig. 17 Pag. 119 EXPERIMENT XIV Figure 20. THis Schematism represents a Vessel full of Water 8 foot deep EF is a Glass-Pipe open at both ends about 9 foot high and one inch in Diameter ABCD is a Vessel of Glass or of any other metal thorow whose orifice above the said Pipe comes down BHI 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 ABCD with Quick-silver almost then pour in as much Water above it as will fill the space ABH 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 CD 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 MN to KL 8 foot and you will find the Mercury to rise in the Pipe from AB to G 6 inches and more The reason is because there is a Pillar of VVater KI 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 HBA and this pressing the surface of the stagnant Mercury AB causes the liquor run up the Pipe from AB to G 6 inches The reason why it riseth 6 inches is this between the surface of the stagnant Mercury AB and the top of the Water LOK 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 BG sink down and become no higher within the Pipe than the surface of the stagnant Mercury AB without The reason is because by coming up above the Water the Pressure of the Water KI is taken away from the orifice I by which means the comprest Air HP extending it self to I liberats the Water ABH 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 KI 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 KI 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 BG suspended as if the Engine were under the Water The reason is because the stopping of the orifice keeps the inclosed Air PH under the same degree of Pressure it obtained from the Water KI 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 HP obtains now its liberty and expanding it self from H to I eases the Water BH 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 KI 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 AB 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 SK that rests upon the top of the Pillar of Water KI for by sucking out the said Air you take away the pondus or weight that counterpoised the weight of the Pillar SK therefore it finding its counterpoise removed presently causeth the Water KI 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 BG and put them into the scale of a ballance then take as much Water as will fill the Tub between AB 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 KH or a Pillar of that hight be able to raise and counterpoise the Mercury BG 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
going down other 17 foot Secondly that 29 inches of Mercury are as heavy as 34 foot of VVater because the Mercury KPN makes a just equipondium with the VVater EHRN 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 KPN be far thicker than the VVater EH 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 heavier 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 Fluids 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 Mercury 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 FE counterpoiseth the Air IK or IS 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 IS have as much Bensil in them as is in the whole Pillar of Air EF 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 IS the Water SK and Mercury KP 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 IS is above the Water SK and the Water SK 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 KP were no thicker than the Water PNRH 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 KS as well as it thrusts down the Water PNRH It may be enquired here how far this Glass would go down before the 29 inches of Air IK 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 PNRH thrust out and not only this but the whole Mercury PK 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 KP were thrust out of their places EXPERIMENT XVI Figure 22. THis Schematism represents a vessel full of VVater 84 inches deep namely from LN the first surface to MR 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 XYO is a surface of stagnant Mercury among which the two ends of the Pipes are drowned EC is a Pillar of Mercury six inches in height and so is GD both of them raised to that altitude by the Pressure of the Water upon the surface XYO The Pillar ECA is supported by and rests upon the imaginary Pillar AP. And so is the Pillar GDB supported by the Pillar BQ 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 Tub 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 XYO Before that the Water is poured into the Vessel there is here a mâ—st equal and uniform Pressure upon the surface XYO 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 pierce the side of the Vessel and when the whole Water is run out he will find EC and GD 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 EC must be six inches seing XYO 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 ZF 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 much Mercury as would fill between XO and ZF 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 same 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 CE and DG within the two Tubs so there are here also two Pillars of Mercury AP and BQ under the two orifices upon which the said two Pillars stand and rest Consider secondly that the Potentia or force of the Pillar AP is just equal to the Pondus of the Pillar ECA Item that the Potentia of the Pillar BQ is equal to the Pondus GDB Thirdly that the Potentia of AP is most exactly equal to the Potentia of BQ and the reason is because their tops A and B are parts of the same horizontal surface I say then if AP be equal to ECA and BQ equal to GDB and AP and BQ equal among themselves then must ECA be equal to GDB The same Water then doth not counterpoise two Bodies of different weight I grant ECA to be far heavier than GDB 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 EC is just the weight of the VVater that presseth upon XYO That 's to say the part of the surface C is no more prest with the Mercury EC than the part X is prest with the VVater LZX 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 AP sustains ECA as easily as BQ sustains GDB Sixthly that in Fluids there is a pondus and a potentia as is clear from the potentia of AP that sustains the pondus of ECA The VVater likewise that sustains hath a potentia and the Mercury EC is the pondus of it Seventhly that there is alwayes equality of weight between the pondus and the potentia So is the potentia of AP equal to the pondus ECA Eighthly that the pondus begets the potentia So the weight of the VVater begets the potentia that's in AP. For make this VVater deeper and you augment the potentia of AP. If you subtract from it the potentia of AP grows less by proportion Or the weight of ECA may be said to beget the potentia of AP. To proceed a little further let us suppose the Air HE 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 IG This comes to pass by vertue of the Pressure of the Atmosphere that rests upon LN From this we gather ninthly that there is a counterpoise between the Air HE and the weight of the Air that rests upon LN and that a slender Pillar of Air is able to counterpoise a thicker for HE is far narrower than LN Tenthly that the Pressure of the Air can be communicated thorow divers kinds of Fluids because the weight that rests upon LN is sent down thorow the VVater LZX 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 LN 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 fiâ—st 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 XYO 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 EC is suspended after and that there is no more difficulty in the one than in the other EXPERIMENT XVII Figure 23 24. Fig. 18 Pag. 116 Fig. 19 Pag. 119 Fig. 20 Pag. 126 Fig. 21 Pag. 132 Fig. 22 Pag. 137 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
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 Hogshead will not sink beyond seven or eight fathom without breaking or busting 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 so 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 pondus 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 GK that 's more and less as the Pressure of the Water KM 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 KG is under the Water KM 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 KM 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 KM that 's within the Glass but only the weight of the Lead Q. 'T is certain he finds not the weight of the Water IH 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 KM 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 KM 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 IH 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 IH 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 broken 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 counterpois'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 Glass-bubble then is EPFR The stem is HC the weight that sinks the Glass is B. The surface of Water under which it is drowned is AD. The Ballance to which the Glass is knit by a string is NO And lastly EFR is the Water that came in and filled the half of the Bubble Now I say it is not the weight of the Water EFR 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 cork 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 EFR that 's now within the Bubble cannot in anywise
burden the Ballance above but must be supported wholly by the Water IKGH 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 IKGH 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 EFR 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 AD. 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 suppoâ—ted 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 six 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 EPF 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 equipondium 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 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 EFR 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 mâ—y 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 dâ—vine 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 Miln-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 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
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 LM to PQ 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 EFGH 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 LM to PQ there cannot be so much VVater expelled now as before seing the space LMPQ 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 LMPQ 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 SN 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 SN 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 therfore cannot burst It 's observable that when a bladder goes far down the sides becomes flaccid and slagging In this case the Air that before had the forme of the
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 PQ to LM 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 heavier 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
The Water EG weighs 672 pound therefore the Air FH weighs as much The Antecedent is clear because EG 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 AB to be 34 foot high and the Pipe EG to be as much I assert then thirdly the Pillar of Air CD 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 AB 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 FH 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 EG weighing 1904 pound the Air FH must weigh as much For if 216 inches of Water weigh seven pound 58752 inches for so many are in the Water EG must weigh 1904 pound Let us suppose secondly the Tub AB to be only 29 inches high and the Tub EG of the same hight and that six inches wide and this 12 inches wide I affirm then fifthly the Air CD to weigh yet 476 pound and the Air FH to weigh 1904 pound Because the Pillar of Mercury AB weighs 476 pound and the Pillar of Mercury EG weighs 1904 pound therefore if AB be 476 CD must be as much And if EG be 1904 FH must be of the same weight I prove the Mercury AB to weigh about 476 pound though it be but 29 inches high because it is 14 times heavier then Water For the same cause doth the Mercury EG weigh about 1904 pound I say about because 34 foot containes 29 inches more than 14 times Let it be supposed thirdly the Pipe EG being 34 foot high to have the one half of it IG full of Air and the other half EK 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 EK 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 IG that bears down the Water KE 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 IG must be as heavy as EH I answer IG is not so heavy as FH because the Water EK impending in the lower part of the Tub hath occasioned the Air IG to expand it self so many inches by which means it loseth so many degrees of it's Bensil If you remove the Water EK then will the Air IG be as heavy as FH because EK being Air it reduceth IG to that same degree of Bensil with it self but when the Air E is burdened with the Water EK it cannot make the Air IG 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 NG 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 EN 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 NG 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 NG 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 EK the Air IG hath the weight of 952 pound Because E being in it self 1904 but being burdened with EK 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 GI 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 EG 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 LM 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 LM 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 LM 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 LM it must either be the Air below namely the part E or the Water EG 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
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 oâ— 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 corn-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 Bellowâ— but did not continue long in sight Such an one above the Fiâ—th 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 surrow 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 as may be The place would be free of Trees or of any such impediment that it may have a free prospect of the Heavens As for their distance one from another let the two North-most and the South-most be two foot asunder let the two East-most and two West-most be but one foot making as they stand an oblong quadrangle For keeping them equidistant above as well as below take four bars of Wood about three inches broad and one inch thick and nail them round about upon the four sides on each side one so that being nailed on Horizontally they may make right angles with the tops of the standards above There are
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 assimilat 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 vapours than liquid juice Indeed some Trees when their root-branches are cut even in Winter will yeeld no small quantity of an acid liquor which by addition of the recent Leffas from the earth smells evidently of the Matrix from which it did proceed Moreover the passages especially from the branches to the Trunk are so straitned and contracted that the bark cleaveth to the Timber as every Wood-man knows But so soon as the warm Spring hath attenuated the ever-flowing juice in the whole Tree then doth it become turgid and more aqueous over all the passages and channels both in the trunk and among the tunicles and particular skinnes are so
is without this force while the Work-men are in the place seems to be this that they working with such violence and motion as they do do certainly move the Air considerably it being contained in so narrow a place as a Coal-room And this Air being violented by motion moves that oily vapour whereof the fire is formed so that it gets not liberty to unit it self being dissipated by the motion of the Air. But so soon as the Air is still and quiet after the Work-men are gone home it units it self and gathers force and therefore so soon as it meets with fire which is more forcible than the flame that is kindled in it it rarifieth the sulphurious parts being kindled and forceth it self out as powder out of a Gun For it hath been observed that if any person stay in the Coal-sink while it breaks within the Coal-room they are in danger of being killed The ordinary way by which the hurt of it is prevented is by a person that enters before the Work-men who being covered with wet sack-cloath when he comes near the Coal-wall where the Fire is feared he creepeth on his belly with a long Poll before him with a lighted candle on the end thereof with whose flame the Wild-fire meeting breaketh with violence and running alongs the roof goeth out with a noise at the mouth of the Sink the person that gave fire having escaped by creeping on the ground and keeping his face close to it till it be over-passed which is in a moment The place where this was most known was in a Coal be-west Leith in a piece of Land called Werdy which for want of Level and the violence of that Fire the Owners were forced to abandon I come now to the last part which I promised to speak of namely of the best way for trying of grounds to find Coal where never any hath hitherto been discovered and of carrying on of Levels for draining the Water of Coals and making it workable As to the first part there are but three wayes First by sinking which is most chargeable in regard that in such grounds where the Metals are all intire Water abounds and this doth not only bring the Master under a necessity of great expence for drawing the Water but also rendereth it impossible to get sinked to any deepness which may suffice for giving an account of all the Metals to be found within the field that may be rendred workable There was a second way invented to supply this defect which is by boaring with an instrument made of several Rods of Iron which boareth thorow the Metals and tryes them This way in my opinion is worse then the former For first if the Coal ly deep in the place where you try by boaring it becomes almost as tedious and expensive as sinking the drawing of the Rodes consuming so much time in regard it must be frequently done Next in boaring suppose the nature of the Metals be found yet thereby their course can never be known till they be sinked which is one of the things most considerable in the search of a Coal because thereby is known whether it be workable with advantage or not and whether it be possible to draw Water from it by a Level or otherwise Lastly this way leaves the Master at an uncertainty notwithstanding the Coal had been found of its goodness as to its nature and as to its thickness As to its goodness because all that is found of the Coal by this boaring instrument is some small dross which remains after the washing of the thing that 's brought up in the wumble by which none can judge of its goodness or badness As to its thickness because it is impossible to discern exactly when the boaring-instrument hath passed the Coal all the rule for trying thereof being the kind of Metal that is brought up in the wumble Now I have known in my experience a Coal boared which the Bâ—arer by that rule hath judged four foot in thickness yet when it came to be sinked hath not proven one The reason whereof is obvious because the boaring-irons being long and weighty in lifting them up and down they break the Coal already pierced and this falling down among the Metals they are piercing and being found in the wumble with them especially when the Metal under the Coal is a black Till gives gâ—ound to imagine that all that time they have been peircing a Coal and so consequently the Coal must be of such a thickness The last and best way of trial is that which is termed an ranging over the Metals For doing whereof this method is to be observed Suppose there be any place within in the ground to be searched where the course of Metals can be seen as in the banks of a River or Rivolet or Sea-banks when the place is near the Sea then consideration must be had how far the lowest of these Metals can go before they Crop out to the Grass which will be known by observing the Dipp or declination of the Metals and the Rise of the ground above whereof a just allowance must be given and having digged before the said Crop you shall certainly find the Metal that is next under it and if that prove not Coal keeping the former proportion you must advance and digg before its Crop and so shall you find the next Metal under it and so still till you have tried your ground and found the Crops of all your Metals within it But if there be no Water-banks or such like to give you the first view of the course of your Metals then must you sink first at random and having once past the Clay you will readily overtake some Metals whereby you will know the course of the rest and having once found the Dipp and Rise you must follow the method of ranging already prescribed except the ground so to be tried contains not within it self the 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 PN where there are several Seams of Metals that Cropps out at the Points KLMN Suppose the lowest to be the Coal viz. IN for which you are to make trial You Digg first at K without the Cropp of the Seam FK and you dig till you find the other Seam of Stone GL 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 HM 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
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 CD 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 EFGH 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 EF 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 EFGH 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