be made exactly congruous to the bottom of the Vessel and consequently the water may get in between them for which cause 't is necessary to keep the woodden Plate forcibly down with a stick which else were needless And consequently this interposed water will communicate with the laterally superior water in the Vessel which superior water may according to the Laws Hydrostatical by the intervention of the interposed exercise its pressure upwards against the lower surface of the woodden Plate Thirdly the Doctors Scheme allows and assists us to conceive which we may do however an imaginary Plane of water to be parallel to the bottom of the Vessel and to pass along the bottom of the Board so that of the water that lies between this Plane and the bottom of the Vessel one part is cover'd by the woodden Plate and the other between the edges of that and the sides of the tub is cover'd with the incumbent water only CHAP. III. THese things being premis'd I thus argue 'T is manifested by Hydrostaticians after Archimedes that in water those parts that are most press'd will thrust out of place those that are less press'd which both agrees with the common apprehensions of men and might if it were needful be confirm'd by Experiments 'T is also evident that that part of the above-mention'd imaginary Plane that is cover'd by the woodden Plate must be pressed by a less weight than the other part of the same Plane because the wood being bulk for bulk lighter than water the aggregate of the wood and water incumbent on the cover'd part of the same Plane must be lighter in specie than the water alone that is incumbent on the uncover'd part of the same Plane and consequently this uncover'd part being more press'd than the other part of the Plane the heavier must displace the lighter which it cannot do but by thrusting up the board as it does when the external force that kept it down is removed And to add this upon the by this greater pressure against the bottom than against the top of bodies immers'd in water specifically heavier than they is a true reason of their emersion as I have elsewhere shewn So that there happens no more in this case than what usually happens in the ascension of bodies in liquors specifically heavier than themselves on the account of the newly mention'd difference of Pressure And 't is with an express or suppos'd exception of such a difference which in many other cases may be safely neglected that which I desire you to take notice of in most places of this discourse I speak of the Pressure of ambient Fluids on immersed Solids as uniform or every way equal 'T is true that according to the Doctors supputation if the solid Cylinder consisting of the woodden Plate and all the water directly incumbent on it were put into an ordinary ballance it would there many times out-weigh the hollow Cylinder of water alone that leans upon the uncover'd part of the imaginary Plane And that is it that seems to have deceiv'd the Learned Doctor But there are divers Hydrostatical Cases wherein the Phaenomenon depends not so much upon the absolute weight of the compared Bodies as upon their respective and their specifick Gravity on whose account it is that a small Pible for instance that weighs not a quarter of an Ounce will readily sink to the bottom of the river on whose surface a log of wood of a hundred pound in weight will float 'T is a Rule in Hydrostaticks that when two portions of water or any other Homogeneous liquor press against each other the prevalency will goe not according to the absolute weight but the perpendicular height of those Portions And accordingly we find that if a slender pipe of glass being fill'd with water have its lower orifice unstop'd at the bottom of a vessel of water which contains much more of that liquor than the pipe yet if this last named water were for instance two foot high and that in the Vessel but one the water in the pipe will readily subside till it come almost to a level with the external water though it cannot do so without raising the whole mass of water that stagnated in the vessel And now I shall subjoin an Experiment which though at first it may seem slight and was made in lesser glasses quantitys than I would have imploy'd if I could have procur'd better Accommodations has the advantage of requiring no curious instruments and yet I hope will serve for an ocular proof of the fallaciousness of that reasoning the Doctor is so strangely confident of We took an open mouth'd glass such as some call Jarrs and Ladys often use to keep sweet meats in which was three inches and a half or better in Diameter and somewhat less in depth and had the figure of its cavity Cylindrical enough Into this having put some water to cover the protuberance wont to be at the bottom of such glasses we took a convenient quantity of Bees-wax and having just melted it we poured it cautiously into the glass warm'd before-hand to prevent its cracking till it reach'd to a convenient height This vessel and the contained liquors we set aside to cool in expectation that when the heat that had dilated the wax was gone it would shrink from the glass and consequently leave a little interval every where between the concave superficies of the vessel and convex of the harden'd wax which accordingly came to pass and sav'd me the labour of getting the wax shap'd for my purpose with tooles which might have been done but not without trouble and less exactness And now 't was easie for me to try the experiment I design'd for pouring in warily some water between the glass and the wax so that it fill'd all the interval left between those two bodys both at the bottom and the sides the wax was made presently to float being visibly lifted up from the bottom and its upper part appearing a little above the level of the water which was no more than I did and had reason to expect according to the true Principles of Hydrostaticks For water being somewhat though but little heavier in specie than wax and that which was poured into the bottom and stagnated there being press'd by the collateral water every way interpos'd between the concave part of the Glass and the convex of the Wax so that this collateral liquor answer'd what I lately called a hollow Cylinder of water in the Doctors Experiment that part of the stagnant water that was lean'd upon by the wax being less press'd than the other part of the same stagnant water was by the water incumbent on it this latter must displace the former which it could not doe but by raising up the wax that lean'd upon it And yet this collateral water was so far from being heavier than the wax its pressure impell'd up that both the collateral and the stagnant water all together being weigh'd
on the outside to what height the Oyl reach'd in it Now if we conceive a Horizontal Plane Parallel to the bottom of the Vessel to pass by the Basis of the floating Wax 't is evident by what has been formerly shewn that of this Imaginary Plane that part on which the Wax is incumbent is as strongly press'd by the weight of the Wax as the Lateral part of the same Plane is by the weight of the Water incumbent on it otherwise these Pressures would not be aequipollent but the Wax would be raised And consequently that part of this Plane that is placed directly over the Orince of the shorter Leg of the Pipe is no more pressed than any equal portion of that part of the same Plane that is cover'd by the Wax This Body being taken out of the Water the Liquor subsided a great way in the Vessel and so did proportionably the Oyl in the longer Leg of the Pipe And lastly having weigh'd out in a good pair of Scales as much Water as we found the Wax to amount to this Liquor was instead of the Wax poured into that which remained in the Glass whereupon the Oyl in the longer leg of the Pipe was again impell'd up very near to the former Marke to which it had been raised by the Wax Whence we may gather that the Water newly put in though in the Air it weigh'd no more than the Wax yet it did as much press the Water that lay beneath the foremention'd Imaginary Plane and consequently that which was directly over the shorter Leg of the Pipe as the Wax that had been taken out had done And since we have already proved that the Wax did confiderably press that Plane it ought not to be denyed that the Water also which instead of it was able to impell up the Oyl in the Pipe did in like manner press that Plane and consequently that Water may gravitate in Water as well as a solid Body such as Wax is can And this is the first additional use I told you I would make of our Experiment But to come now to the second there is another Phaenomenon of it viz. the abovemention'd tenderness of Nature's Ballance whose use seems to be of no less general concernment to the true Doctrine of the Hydrostaticks For by duely considering that Phaenomenon and reasoning a while upon it we may be help'd to rectifie that plausible Mistake which has long deluded both Philosophers and Mathematicians and does yet impose on most of them namely that a Body does not actually gravitate when it does not descend For we have seen already and shall further shew by and by that the sunken Wax and the Brass grains that lie on it do actually press or gravitate upon the subjacent Water and Bottom of the Vessel on which 't is incumbent and consequently its pressure being not surmounted by that of the Collateral Water which is unable to raise it must be as great as that of this collateral Water Therefore when upon the removal of a single Grain the Wax with its incumbent weight is made to ascend and that but very slowly 't is evident that 't was so far from not gravitating before because it did not actually descend that it retain'd its Gravity even whilst it ascends As may appear not only by the slowness of its motion upwards proceeding from its being in Nature's Ballance very little less heavy than it need be to countervail the pressure of the Collateral Water but by this also that if but a single grain be laid on it when it begins to rise its ascension will be check'd and hindred which could not be done by the addition of so inconsiderable a weight if the Wax and the adhering Metall did not even during their ascent retain their former gravity though that were frustrated as to the act of descending or so much as keeping their station by the prevailing pressure of the collateral Water So that since as we found the Wax and adhering Metall amounted to a good deal above 4000 Grains it did in the Ballance of Nature weigh whilst it was ascending not so much as a 4000th part less than it did whilst it was actually descending CHAP. V. I Should beg your pardon Sir for having detain'd you so long with my Reply to a single Objection of the Doctors how pompously soever propos'd but that I thought it not amiss to do some service to the true Theory of Hydrostaticks by taking this occasion to present you some things that I thought not unlikely to illustrate some parts of that Theory though above what was necessary to answer the Doctors Argument to which I confess I was troubled to see so Learned a man subjoin the following conclusion Haec tam luculenta Demonstratio contra Gravitationem particularum aquae inter se quamvis junctae situlae fundum urgeant si non sit vera atque solida equidem nec mei ipsius nec ullius unquam mortalis in posterum ratiociniis credam But I hope he will not be as bad as his word but will be pleas'd to consider as well as I do for him that a man may be very happy in other parts of Learning and of greater moment that has had the misfortune to mistake in Hydrostaticks a discipline which very few Scholars have been at all vers'd in and about which divers of those few have had the misfortune to err not only in the conclusions they have drawn but in the very Principles they have embraced To the foregoing Argument the Doctor though he declares he thinks it needless adds in the 5th Paragraph another taken from the Last experiment of my Hydrostatical Paradoxes by which he ingenuously acknowledges that I seem at first sight to have demonstrated what I pretend to about the gravitation of the upper parts of stagnant water upon the lower And I am sorry that I cannot in return acknowledge that his objection at first sight seem'd to me a cogent one For neither at the second nor third perusal can I clearly discern where his Ratiocination lyes supposing it to be meant for an answer to my experiment And though I consulted with some Learned Members of the Royal Society whereof two are Mathematicians and one his particular friend yet they all confess'd he had not sufficiently explain'd himself on this occasion nor could they shew me to what argumentation I might properly direct my reply Only one of the Doctors Correspondents having seriously perus'd his discourse and the annex'd scheme told me that what seem'd the most probable to him was that though the Doctor was too Civil to give me in ter ninis the Lye yet he did indeed deny the matter of fact to be true Which I cannot easily think the Experiment having been tryed both before our whole Society and very Critically by its Royal Founder his Majesty himself But since you have your self seen and made it more than once I need not spend words to convince you that the
could not by them be ascribed as before to the recess of the Air endowed as they suppose with positive Levity but to the weight of the admitted Water which when thus weighed would be inviron'd with Water of the same kind And to shew that this admitted Water might have a considerable weight notwithstanding the place it was in I imployed a pair of scales after the manner that is recited in the Experiment By what I have been discoursing you may conceive that however my expressions disagree with those of my Adversary the distance of our opinions is not so wide as at first sight it seems For he allows as well as I that the superiour parts of Water do by their Gravity for I know not on what other score they can do it press the inferiour But this he would not have amount to this expression that water weighs or gravitates in water whereas I scruple not to cloath my sence in that expression because I think water does always exercise its gravity though it does not always pregravitate or actually descend being often as I noted above either impell'd up by an opposite and prepollent weight or hinder'd from descending by the Resistance of other water that counterpoises it so that if he thinks that in my Experiment I meant to propose a method of making Water descend in Water and weigh it in that Liquor with a pair of scales just as if I would weigh in the same Water a piece of Lead or a portion of Mercury which are bodies much heavier in specie than Water either he mistakes my intention or I did not sufficiently declare it But that which I designed to shew and for ought I can yet see have shewn was that by the help of an ordinary ballance it may be made appear that Water admitted into the Glass-bubble I imployed did make the Glass-bubble weigh so much heavier than it did before that Liquor enter'd into it and that this new weight that was manifested by the ballance was not due as my Adversary supposed to such a recess of the Air as I mention'd a while ago And now Sir It will be proper to take notice of some passages in the Objectors Discourse in order to dilucidate the subject of it Whereas he sayes page the 149. 150. Take a piece of wood that is 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 and weigh it in Water and you will find the whole weight supported by the water I answer that this does not at all overthrow my opinion but agrees very well with it For suppose the weight you add to the light wood be Lead it cannot be said that the Metal loses its native ponderosity whilst it rests in the Water and the reason why it descends not is that it and the wood it is joyn'd to are hinder'd by the counterpoise of the Collateral Water which by its pressure would raise the surface of the Water whereon the floating or swimming body leans if it were not hinder'd by the weight of these incumbent Solids And this Resistance of theirs to the endeavour upwards of the Water being exercised only upon the account of their Gravity shews that they do in my sence gravitate though not pregravitate Again if you please to consider the case put by the Objector page the 151. and cast your eyes upon his Scheme which supposing you to have his book I shall for brevities sake make use of at present you will find him thus argue * Vid. page 151. Now I say 't is six ounces of the weight B that makes this alteration and turns the scales For if 12 ounces sink the Glass below the Water when it is 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 6 inches of Air by the one half to counterpoise a weight of 12 ounces than in 12 inches of Air. Therefore this Air being reduc'd from 12 inches to six it must take only 6 ounces to sink it To which I answer that I know not yet what on this occasion he means by a potentia or force in 6 inches of Air to counterpoise a weight of 12 ounces For by the term counterpoise where the Question is about Weighing one would think he speaks of Weight and yet Air according to the vulgar Opinion is positively light according to us though it have a gravity yet in our case that must amount to so little that what Air the bubble needed to fill it could not weigh at most above 4 or 5 grains which therefore might safely be neglected But according to my opinion the reason of the Phaenomenon is clear enough without medling with the Potentia of the Air. For if we conceive a horizontal Plane to divide the Water mentally and pass by the bottom of the suspended bubble before the little stem be taken off there is a far greater pressure upon the other parts of that Plane than upon that which lies under the bubble in regard they are prest by the weight of the Collateral Water A L G D M C whereas the other is prest only by the weight of a body very much lighter than its equal bulk of water so that to keep the bubble from being forcibly buoyed up there was requisite 18 ounces of Lead that make up the Plummet B to detain it under Water and keep the beam of the ballance Horizontal that when access is given at C to the neighbouring Water it is by the weight of the collaterally superiour Water impell'd into the cavity of the bubble where the Air being much rarified before could not resist its ingress and thereupon 6 ounces of Water getting in that part of the imaginary Plane on which the bubble was incumbent is prest by a greater weight than formerly by 6 ounces and consequently there needs the like weight in the opposite scale of the ballance to reduce the scale to an Aequilibrium And if we suppose with our Author the Glass to be compleatly full of Water and the counterpoise in the scale O to need 6 ounces more to make a new Aequipondium the account of the Phaenomenon will be the same as if you attentively consider it you will clearly perceive And the reason why the additional weight of 6 ounces is required will be that the upper half of the bubble that before contained less than three or four grains weight of the Air being now fill'd with Water amounted to six ounces more of Water than formerly and so the counterpoise in the opposite scale O will need the weight of six ounces to make a new Aequipondium Congruously to this explication when the Examiner says * page 132. Now I inquire whether these 18 ounces are the Aequipondium of the Water within the Glass or of the
weight of the Lead B 'T is impossible they can counterpoise both seeing the Water 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 Aequipondio with 18 it must then be in the second Or if these 18 ounces in the scale O be the counterpoise of the Water within the Glass I inquire 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 answer that this specious objection seems for it is somewhat obscurely worded to be founded upon a mistake of my meaning in the Question However as to the Phaenomenon it self according to my sence the 18 ounces in the scale O are the counterpoise of the 18 ounces that hang from the opposite and aequidistant Scale and make up the Leaden Plummet B which answer I see not how our Author prevents But then you will ask what counterpoises the Water in the bubble which alone weighs 12 ounces I answer that 't is the gravitation of the collateral Water which presses the other parts of the lately mentioned imaginary Plane as much as the Water in the bubble the weight of the Glass being here not reckon'd by either of us and the Water incumbent on the bubble does press that part of the Plane on which they lean so that there being in all 30 ounces to be sustained the 18 of the Plummet and the 12 contained in the Glass the Lead that hangs in the Water is counterpoised by 18 ounces in the scale and the Water in the bubble by the pressure of the Collateral Water But you will say that it appears not that the included Water presses at all since it does not at all descend To which I answer that as long as the Water was getting into the Cavity of the bubble so long it did manifestly gravitate upon the subjacent Plane and actually descend raising the counterpoise in the scale But when by adding more weight to that counterpoise things are brought to a new Aequilibrium there is no reason why the gravitation of the VVater should again change the now regain'd Aequipondium Suppose in the two scales of a ballance there were placed two equally capacious and equiponderant Vials whereof one is quite full and the other almost full 't is evident that the full Vessel will keep the scale it lean'd upon deprest and if you gently pour in as much VVater into the unfill'd as the fill'd has more than it the scale that was formerly kept rais'd will be now deprest till the beam be brought to be horizontal to which posture when it is once brought the Aequilibrium will continue And yet it will not be said that though the added VVater whilst it was filling the Glass deprest the scale it belonged to yet it lost its weight or which in my sence is all one did not gravitate upon the Scale when the ballance was come to an Aequilibrium because then this VVater did no longer depress it And how much the VVater in our bubble does notwithstanding its immersion gravitate would be visible if by supposition it were all annihilated and no other suffer'd to supply its room For then the subjacent part of the imaginary Plane being much less prest than immediately before the weight of the collaterally superiour VVater would strongly impell up the bubble if it were not kept in its place by a proportionable addition of weight to the Plummet Nor should it seem a strange thing that I should say that the 30 ounces lately mentioned should be counterballanced partly by the weight in the opposite Scale and partly by the VVater that fills the immers'd bubble since this notion may be warranted even by the common practice of weighing heavy Solids Hydrostatically For if you would for instance weigh a lump of Copper of 9 pound in common VVater the Metal hanging by a Horse-hair under VVater will need according to my elsewhere mention'd Experiments either just or near about 8 pound in the opposite Scale to keep the ballance horizontal so that the whole 9 pound that the lump weighed in the Air is counterpoised partly by the 8 pound newly mention'd in the opposite Scale and partly by the weight or resistance following from weight of as much of the VVater as the Copper fills the room of which as experience shews is one pound And if we should conceive VVater in a Vessel adiaphorous as to Gravity and Levity to be substituted in the place of the Metalline lump it would weigh as much as the ninth part of the Copper-lump weighed in the Air and the same counterpoise of eight pound would maintain the Aequilibrium What the Learned Objector has at the close of his Discourse about the natural and artificial ballance could not without prolixity and is not here necessary to be dwelt upon especially since you will see in what I suppose you have now received from the Press in answer to the Ingenious Doctor More what is to be said on that Subject according to my Hypothesis VVherefore though my Learned Adversary does in the 152. page conclude That Water cannot weigh in Water and asserts that the Pressure of VVater is one thing and VVater to Weigh in VVater is another yet as I said at first I conceive much of our Difference may be verbal and in my sence when VVater presses subjacent VVater because it does so upon the score of its gravity it gravitates in VVater though it does not pregravitate that is actually descend And since 't is in the sence of this last expression that our Author if I mistake him not speaks of weighing in VVater his conclusion that VVater cannot weigh in VVater does not contradict me who affirm not that VVater does so weigh in VVater VVhether we shall agree in all other points of Hydrostaticks you will easily believe that I cannot yet tell though by the expression he is pleased to use in the 146. page to usher in his Objection with 't is probable we may And as to the now dispatch'd debate if I have imployed some words in another sence than he I presume he is so equitable as to consider that I did not write of these things after having seen this book of his but some years before and have since found those expressions justified by the use that eminent VVriters have thought fit to make of them And however I am glad that he has given me this opportunity of clearing my Experiment and declaring by examples as well as words the opinion it relates to especially if it seems to others that I omitted to express my self so fully my design being as I formerly told you to convince such Adversaries as I then had met with by shewing that the above-recited Phaenomena of the Emersion and Sinking of a Glass-Vial depended upon
the Hydrost Paradox And therefore there is no reason why the Divers bodies should be more forcibly depress'd than its depression is resisted 'T is true that this body will sink but that is because 't is not only as we lately suppos'd it aequiponderant to an equal bulk of water but heavier than that But then since the Water by its gravity and resistance takes off as much of the weight of the Divers body whilst that is immers'd as a quantity of water equal to it would weigh in the Air the subsiding of the humane body by its own weight ought to be but slow because that being not in specie much heavier than water it can sink but by virtue of the surplusage of weight that it has above water And in effect I have been informed by Swimmers that in the Sea whose water by reason of the Saltness is specifically heavier than the common water they could hardly dive when they had a mind the salt-salt-water did so much support them And having because I had no conveniencies to make tryals upon the parts of humane bodies examin'd the weight of parts of other Animals in Air and Water I found the overplus of the weight of the animal substances above an equal bulk of water to be but very small And this may suffice to take off the wonder why though water be admitted to gravitate in water yet Divers are not depress'd by that which leans upon them the endeavour they use to keep themselves from sinking by striking the resisting water with their arms and legs easily compensating their weak tendency downwards which the small surplusage of gravity above-mentioned gives them But it seems to me far more difficult to render a reason why those that are a hundred foot beneath the surface of the Sea are not crush'd inwards especially in their chests and abdomens or at least so compress'd as to endure a very great pain To clear up or lessen this difficulty I have two things to offer 1. I confess that I am not intirely satisfied about the matter of fact for I do not yet know whether it fares alike with the Divers at all depths under water for according to the answers I obtain'd from persons that had been one of them at the Coral-fishing in the Streights and the other at the Pearl-fishing near Manar I do not find that the Divers are wont to descend to the greatest depths of the Sea which if they did perhaps they would find a notable difference And in small or but moderate depths those that dive without Engines usually make such haste or are so confounded or have their minds so intent upon their work that they take not notice of such lesser alterations as else they might observe especially they being persons void of curiosity and skill to make such observations Which I the rather mention because having met with a Learned Physician that living by the Sea-side in a hot climate delighted himself much in diving and inquiring of him whether he felt no compression when he passed out of the Air into the Water he answered me that when he div'd nimbly as others use to do he took not notice of it but when he let himself sink leisurely into the water he was sensible of an unusual pressure against his thorax which he several times observed A man that gets his living by fetching up goods out of wrack'd Ships complain'd to me that if with his diving Bell he went very deep into the Sea and made some stay there he found himself much incommodated which though he imputed to the coldness of the water yet by the symptoms he related I was inclin'd to suspect that the pressure of it upon the Genus Nervosum might have an interest in the troublesome effect And I have been assured by an eminent Virtuoso of my acquaintance that he was lately informed by a person whose profession it is to fetch up things from the bottom of the Sea by the help of a diving Bell that several times when he descended to a great depth under the surface of the water he was so compress'd by it that the blood was squeez'd out at his Nose and Eyes which Relation seems to favour our conjecture and would much more confirm it if I were sure that the effect was no way caus'd by some fermentation or other commotion in the blood it self occasioned by the great density or other alterations of the Air he breath'd in and out or by some other operation of the ambient Medium distinguishable from the compression of the water though perhaps conjoyn'd with it And on this occasion I remember that questioning an Ingeneer who had made use of an Engine to go under water quite differing from the Diving-bell he answer'd me that when he came to a considerable depth he found the pressure so great against the Leathern case wherein he descended and by that means against his belly and thorax that he feared it would have spoiled him which forced him to make haste up again But this observation to have much built upon it should be further inquired into These things and not these only make me wish that what is felt by those that dive to great depths and stay at them might be more heedfully observ'd by intelligent men that being fully inform'd what is true in point of fact we may the better and more chearfully indagate the reasons In the mean while taking things as they are thought to appear I shall propose two things towards the solution of our difficulty namely the Firmness of the structure of a humane body and the Uniformity of the pressure made by fluids Of the first of these I shall add but little to what has been already said where I spoke of the resistance made by our bodies to the compression of the Atmosphere only shall here take notice that whereas the Membranes are very thin parts and therefore seem unfit to make any great resistance we have tried that if a piece of fine Bladder were fasten'd to the orifice of a Brass-pipe of about an inch in Diameter we could not by drawing the Air from beneath it make the weight of the Atmosphere break the bladder though the weight were perhaps aequivalent to an erected Cylinder of water of the wideness of the orifice and about 30. foot high and weâ—e indeed such that divers men that laid their hands on the orifice when the Air was pump'd out from beneath complain'd that they were not able to lift off their hands again till some of the Air was readmitted But the main thing I shall propose towards the solving of the difficulty we are considering is the Uniformity wherewith fluid bodies press upon the solid ones that are placed in them And because I remember not to have met with Experiments purposely made to shew how this sort of pressure is more easie to be resisted than that of solids against solids I shall subjoyn the following tryals EXPER. I. IN the short Cylinder
TRACTS Written By the Honourable Robert Boyle CONTAINING New EXPERIMENTS touching the Relation betwixt Flame and Air. And about EXPLOSIONS An HYDROSTATICAL Discourse occasion'd by some Objections of Dr. Henry More against some Explications of New Experiments made by the Author of these Tracts To which is annex't An Hydrostatical Letter dilucidating an Experiment about a Way of Weighing Water in Water New Experiments Of the Positive or Relative Levity of Bodies under Water Of the Air 's Spring on Bodies under Water About the Differing Pressure of Heavy Solids and Fluids LONDON Printed for Richard Davis Book-seller in Oxon MDCLXXII Advertisement to the Book-binder SOme of these Tracts having been misplaced in the printing the Book-binder is desired to take care of placing the several Tracts in the order as they stand in the Title-page as also to observe in the binding the Advertisement given p. 131. immediately following after the Experiments about the Relation betwixt Air and the Flamma vitalis of Animals NEW Experiments Touching the Relation betwixt Flame Air And particularly betwixt AIR and the Flamma Vitalis of Animals To which are annexed Two Attempts the one to produce Living Creatures in Vacuo Boyliano the other made upon Gnats in the same Vacuum THE PUBLISHER TO THE READER IT will 't is presum'd be altogether needless to preface any thing by way of commendation to the following Tracts they will certainly commend themselves by their own worth to the Intelligent and Attentive Reader who might have seen them sooner if the Press had not detain'd them longer than was expected since to the Publisher's knowledge they were ready in the Year 1671. except the Hydrostatical Discourse and the Explication of the Author's Experiment of Weighing Water in Water the former of which was finish'd in the beginning of this Year 1672 though the latter could not be so till near the end of the same Year viz. the month of February English stile because the Book of Mr. George Sinclair's Hydrostaticks in which it is excepted against came not I think before that time to London I am sure not to the view of the Honourable Author Farewell NEW EXPERIMENTS Touching the Relation betwixt Flame and Air Sent in a Letter To the Learned Publisher of the Philosophical Transactions SIR YOu may have observ'd as well as I that since the publishing of the Experiments I sent you touching Respiration divers of our Learned men have spent both Thoughts and Discourses in inquiring and disputing Whether there reside in the heart of Animals such a fine and kindled but mild Substance as they call a Vital Flame to whose preservation as to that of other flames the Air especially as 't is taken in and expell'd again by Respiration is necessary This among other considerations makes me think it seasonable though many avocations make it inconvenient to compleat the performance of the Promise I made you by adding to the Experiments about Respiration which your commands have already obtain'd of me those scatter'd Notes that I have been able to pick up about the Relation betwixt Flame and Air And though I confess they are very much inferior in number to the Tryals about Respiration and that in making them it was not so much my Design to compleat an intire and distinct Tract though but a small one of such Experiments as to gratifie my own curiosity in the examining of a Paradox or two I had been writing about Flame yet the nobleness of the Question now under debate and their pertinenoy to it will possibly keep them as few as they are from being useless And that also they may be the better kept from being unwelcome I have chosen to make my self a Relater of matters of fact without ingaging with either of the Litigant parties in a Controversie wherein I am the less tempted to be partial because I have not formerly declared my opinion about it and at present I see on either side Persons for whom I have no small respect and kindness And now Sir that you may not expect in the following Papers such a number and variety of Experiments as I might perhaps be able to present you with on some more tractable subject I shall briefly mention to you some of the chief difficulties I met with in the making of these which I do the rather that if you and your ingenious friends have a mind to prosecute such Tryals you may not be surpris'd with the difficulties I have met with but provide at least against those fore-seen ones by which you will scarce fail to be encounter'd I shall then inform you that the ensuing experiments were rendred uneasie and troublesome to me by this that some of them could not be conveniently done at all seasons of the year nor in any season in all weathers but must be made not only in the day time but in Sun-shine days You will easily ghess that I speak of those experiments that are to be made by the help of a Burning-glass casting the reflected or refracted beams of the Sun upon the combustible matter plac'd in the exhausted Receiver For by reason of the interposition of so thick a Glass whereby many of the incident beams of Light are reflected and others inconveniently refracted there is ordinarily requisite a clear day and a competent height of the Sun above the Horizon and sometimes also a convenient time of the year to bring such experiments as we were speaking of to a fair Tryal Not to take notice that in such attempts there usually intervene circumstantial difficulties not so easie to be fore-seen And it not being Summer when I had occasion to make the following Experiments I could make but very few with the Sun-beams besides that there are divers others which are not that way to be made so conveniently if at all as by the help of the Fire But though the Tryals of this second sort had their conveniencies in regard they might be made in any weather and as well by night as day yet they were not unattended with peculiar inconveniencies some of which you will easily discern by the mention of them that was necessary to be made in some of the relations themselves And besides more particular and emergent difficulties there was this in general that render'd these Experiments troublesome that whether I made them in larger Receivers or in small or in middle-sized ones each of these cases had its inconveniencies For very large Receivers besides that 't was very toilsome and tedious to empty them of Air required so much time for the exhaustion that too frequently by that time the Operator had done pumping the included Iron or other heated body was grown too cold to perform the desired effect And if the Receiver were not considerably large then the red-hot Iron or other included body that was to burn the combustible matter would much endanger the breaking of the over-heated Glass and not afford room enough for some Phaenomena to be fairly exhibited in and
to usher in with a complement to me that I should be very vain if I looked upon as any thing more than a Complement To his first Objection propos'd in these words * 139. Primò enim si haec solutio verè mechanica sit quae tandem Causa verè mechanica assignari potest gravitationis singularum particularum totiúsque atmosphaerae in suis locis Nam quod materiam subtilem attinet c. I answer that I did not in that Book intend to write a whole Systeme or so much as the Elements of Natural Philosophy but having sufficiently proved that the Air we live in is not devoid of weight and is endowed with an Elastical Power or springiness I endeavour'd by those two Principles to explain the Phaenomena exhibited in our Engine and particularly that now under debate without recourse to a Fuga Vacui or the Anima Mundi or any such unphysical Principle And since such kind of Explications have been of late generally called Mechanical in respect of their being grounded upon the Laws of the Mechanicks I that do not use to contend about Names suffer them quietly to be so And to entitle my now examined Explication to be Mechanical as far as I pretend and in the usual sence of that expression I am not obliged to treat of the cause of Gravity in general since many Propositions of Archimedes Stevinus and those others that have written of Staticks are confessed to be Mathematically or Mechanically demonstrated though those Authors do not take upon them to assign the true cause of Gravity but take it for granted as a thing universally acknowledged that there is such a quality in the Bodies they treat of And if in each of the Scales of an ordinary and just Ballance a pound weight for instance be put he that shall say that the Scales hang still in Aequilibrium because the equal weights counterpoise one another and in case an ounce be put into one of the Scales and not into the opposite he that shall say that the loaded Scale is depress'd because 't is urged by a greater weight than the other will be thought to have given a Mechanical Explication of the Aequilibrium of the Scales and their losing it though he cannot give a true cause why either of those Scales tends towards the Center of the Earth Since then the assigning of the true cause of Gravity is not required in the Staticks themselves though one of the principal and most known of the Mechanical Disciplines Why may not other Propositions and Accounts that suppose Gravity in the Air nay prove it though not à priori be look'd on as Mechanical CHAP. II. THe next thing the Doctor opposes to my Explication is a resolute Denial that there is any such Gravitation as I pretend of Bodies or their Particles in their proper places But because for the proof of his negation he refers us to the next Chapter we shall hereafter have a fitter place than this to consider it in Thirdly he tells us we may justly doubt of the equal diffusion of the Springy power or the Pressure of the Air every way In what sence in some cases I admit of a small inaequality between the pressure of Fluids against differing parts of a surrounded body I have * See the Hydrostatical Paradoxes esp cially Parad. 7. elsewhere declared and need not here discourse of since in the case before us and in the like that Pressure is inconsiderable enough to be safely neglected And whereas our Author thus argues * p. 139. Semotâ vi Elasticâ particulae tamen Atmosphaerae deorfum tenderent Est igitur depressio quaedam deorsum praeter vim Elasticam ipsi superaddita sursum non item sed elastica sola éstque suppar ratio in pressionious transversis obliquis I presume he did not sufficiently consider our Hypothesis and the nature of the pressure of Fluid Bodies that have weight For Water to which no Springiness is ascribed as there is to Air but which acts by its weight and fluidity is able upon the score of those Qualities to buoy up great Ships that the ebbing Tide often leaves upon the strand And whereas the Learned Examiner proposes a fourth Objection in these terms * p. 139. Quibus omnibus addas difficile esse intellectu si unius Cylindri Atmosphaerae pondus aequalis diametri cum Embolo reflectione in fundum Emboli derivetur cur non quinque alii Cylindri Aeris qui circumstant Embolum in ejus fundum eodem modo simul agere possunt ita ut vis sursum impellens Embolum sextuplo major sit quà m hactenus ab bujus opinionis fautoribus existim ita est Quod si sit tunc certe siquo artificio fieri possit ut unius solius Cylindri actio in Embolum admitteretur re iquorum quinque exclusa pari tamen facilitate Embolus ascenderet manifestum indicium esset ne unum quidem Cylindrum Atsmosphaerae agere in fundum Emboli sed totam Hypothesin ingeniosam tantummodo esse fictionem I presume Hydrostaticians will think this might have been spared For they will tell him that there can no more of a fluid press directly upward against the Cylindrical Orifice of a Body immers'd in that fluid than a Cylinder of that fluid of the same diameter with the Orifice the lateral pressures bearing against the lateral parts of the Cylinder And therefore if you invert for instance a Pipe open at both ends and filled to a certain height with Oyl into common water the Oyl that is kept up by the pressure of the water upwards will keep at the same height as to sense whether the Vessel that contains the Water be broad or narrow provided it be somewhat larger than the Orifice of the Pipe And now to invalidate yet further the precedent Objections made by the Doctor I shall add that it need not be thought incredible that the Atmosphere by its weight or the Spring of the Air compress'd by that weight should be able to raise up fourscore or a hundred pound hanging at the Sucker Since I have * See Continuat of New Exper. Physico-Mechan Exp. 48. p. 165. manifested two or three years ago by a clear and cogent Experiment that a little air included in a Bladder will by its meer Spring be able to heave up a weight of a hundred Pound and this without the help of any rarefaction by heat By which Experiment may be also confirmed what I deliver'd a while since about the endeavour of the Air that is wont to be included in our brass Cylinder by expanding it self to thrust away the Sucker which in regard of the structure of the Pump it can do no otherwise than downwards with a depressing force aequivalent to the pressure upwards of the Atmosphere against the external part of the same Sucker CHAP. III. BUt I shall not insist upon the foregoing Objections because the Learned Doctor himself
the following Papers By which it appears that the pressure of the Atmosphere is exercised as indeed I do not see what should hinder it from being even upon Bodies that are quite immers'd under water and by which added to what has been hitherto discours'd in answer to the Learned Doctors Objections you will easily judge how deservedly he shuts up the Arguments we have been examining with this Conclusion * p. 143. Adeo ut extra omnem controversiam positum videatur quòd nulla est ejusmodi vis elastica in aere qualem è doctis nonnulli supponunt multoque minus tam fortis ut centum librarum pondus superet Quod erat Demonstrandum CHAP. V. BUt this is not all the Doctor urges against me in this Chapter for in the 14th Paragraph he seconds his former argument by another drawn from this Experiment of mine That having taken two round Marbles whose surfaces that were to be contiguous were as well ground very flat as carefully polish'd and having placed them one directly upon the other they did in a horizontal posture so firmly cohere without the help of any Glue See the Hist of Fluidity and Firmness p. 222. of the second Eâ—ition or viscous Body that the upper Marble being pull'd up would take up the lower though clogg'd with a weight of fourscore and odd pounds This Experiment when I many years ago first publish'd it I referr'd to the action of the Atmosphere which pressing equally and strongly against the surfaces of both the Marbles except where they were contiguous the higher could not be drawn directly upwards from the lower and consequently must be follow'd by it by a less force than that which was equivalent to the weight of as great a Cylinder of the Atmosphere as lean'd upon the upper Marble This Experiment thus explain'd though it hath been judged a very favourable one to the Hypothesis on whose behalf I alledged it does yet to the justly famous Doctor seem a very considerable Argument against it though for this judgement of his he urges only this reason That if the force with which the Air presses the lower Marble against the upper be able to sustain that Marble though clogg'd with the great weight above mention'd the same pressure of Air would much more easily support a Plate of wood brought to a true plain and not loaded with any weight if the wooden Plate were substituted to the lower Marble and instead of it applied to the upper But since the Experiment as I proposed it did upon tryal succeed very well it had not been amiss if the Learned Examiner had consider'd it as it was really and successfully made and shewed why the pressure of the ambient Air was not able to hinder the separation of the Marbles And his needless substitution of a Wooden plate instead of the lower Marble easily suggests a suspition that there may lie some fallacy though not intended by him in the variation he proposes of the Experiment And he seems to have himself had thoughts of this kind by taking notice that it may be answer'd on our behalf that a Wooden Plate cannot be so exactly applied to the upper Marble but that there will be a little Air intercepted between it and the bottom of that stone And though having granted that it may be so he employes two pages to shew that this intermediate Air could not keep the pressure of the Atmosphere from supporting the unclogg'd plate of wood if it had been That pressure which when there was no such intermediate Air had sustain'd the lower Marble with all the appendant weight yet I confess his Proofs seem not to me to be answerable to the Assurance he uses in speaking of them His Examples taken from Gunpowder and Wind you will easily judge not to be very proper where we are not considering a force that acts by a sudden and vanishing Impetus but a constant and equal pressure And as to his other Instance which is taken from five men that thrust against the sixth standing with his back to a Wall who is but as strong as any one of them I answer that neither is this example near enough of kin to our case For each of these five men is supposed to have an equal power of thrusting proper to himself and independent from all or any of the other four And the sixth man is likewise supposed to resist but by his own single force without having his power of reacting increas'd by the force wherewith the others thrust against him But in our case the thing is quite otherwise for supposing that some aerial particles be so placed that a solid Body hinders them to recoil or expand themselves we are to consider that as the contiguous corpuscles of air press against them not by their own single weight or pressure but as they transmit the action of all the other particles of the air which by their weight or pressure thrust them on so the aerial particles contiguous to the solid Body resist not barely by that force which they would have if they were not compress'd but by vertue of the Springiness they acquire upon the score of the forcible inflection they sustain from the action of the corpuscles that either mediately or immediately thrust against them and consequently in proportion to that external force the Elasticity of these compress'd Particles will be increased as we see that a Bow or other Springy body the more it is bent by an external force the greater power it has to resist further compression Upon which grounds it need to be no wonder that a small portion of Air being almost included in a solid Body and having for some though but very little time been exposed to the outward air should be capable of resisting the pressure of as much of the whole Atmosphere as can come to press against it For this pressure of the Atmosphere being continual if the Springiness of the aerial particles were not now great enough to resist that pressure they must necessarily have been before-hand inflected or compress'd by it till the endeavours of the one and the other were reduced to an Aequipollency Of which I shall give you an instance in so obvious a body as a Bubble at the top of water For though there be but a little Air included in a very thin and transparent film of water yet this little air is so well able to resist the weight of all the Atmosphere that can come to bear against it that all the pressure of it is not able to make the film shrink or become wrinkled which it would do if the corpuscles of the Internal air were not reduced to a Springiness which makes its power of resisting equal to the endeavour of the External Atmosphere to compress it And to let you see that we may well conceive such a Springiness of the air included in the Bubbles I have elsewhere related how by barely withdrawing the pressure of the
in good scales amounted to little above a quarter of the weight of the wax which happen'd by reason of the narrowness of the Vessel which if it had been wide enough I doubt not but the experiment would have succeeded though the wax had outweigh'd the collateral water ten times more than in our experiment it did But that the solid body exceeded almost four times the weight not onely of the collateral but the stagnant liquor too does sufficiently overthrow the Doctors ratiocination Whose fallaciousness will yet further appear by two other improvements among others which I made of one Experiment For I. though we pour'd in more and more water as long as the Vessel would contain any the Cylinder of wax was but lifted higher and higher from the bottom of the glass but did not appeare rais'd more than at the first above the upper surface of the water which argues that 't was not at all the Quantity of the inferior water which was continually increas'd but the pressure of the collateral water which continued still at the same height in reference to that wax that caus'd the elevation of the body And II. to manifest yet more clearly the Doctors mistake I devised the following tryal We took a round plate of Lead about the thickness of a shilling and having made it stick fast to the bottom of the Cylinder of wax to make this body sink the more directly we placed one after another upon the upper part of the wax divers grain weights first wetted to keep them from floating till we had put on enough to make the wax subside to the bottom For the facilitating whereof we had par'd off its edges by this means the glass having been at first almost fill'd with water there swam about an inch or better of that liquor above the upper surface of the wax And lastly we took off by degrees the grain weights that we had put on till we saw the wax notwithstanding the adhering Lead rise by degrees to the top of the water above which some part of it was visibly extant From this experiment I thus argue 'T is manifest that according to the Doctors supposition here was incumbent upon the wax a Cylinder of an inch in height and of the same Diameter or breadth with the round surface of the wax whereas upon the removing part of the water that lay at the bottom when the wax began to rise there was incumbent no greater weight than that of the collateral water and as much of the superior and stagnant as was directly imcumbent upon that collateral water and would have deserv'd the same name if we had suppos'd the convex surface of the wax to have been continued upwards as high as the glass reach'd But now whereas according to the Doctors ratiocination this Cylinder of water incumbent on the wax being an inch deep and a good deal above three inches broad must press the wax with a greater weight by several times than that which the lateral and hollow Cylinder of this stagnant water could have upon the rest of the collateral water yet the height of this aggregate of collateral waters being the same with that of the wax and the water swimming upon it the difference of the pressure was so small that barely taking off a weight of four or five grains the wax would notwithstanding the pressure of the water incumbent on it be impell'd up and made to float And by the like weight put again upon it it would be made to sink and by another removal of such a weight for I purposely reiterated the tryal more than once it would though slowly reascend And these Phaenomena do so much depend upon a Mechanical aequipollence of pressure that even four grains would not have been necessary to make the wax rise or sink if it had not been for some little accidental impediments that are easily met with in such narrow glasses for otherwise in a larger Vessel we have made the same Lump of Wax readily enough sink or float by the putting in or taking off a single grain or perhaps less By this you may see that for the Regulation of Hydrostatical things Nature has her ballance too as well as Art and that in the ballance of Nature the Statical Laws are nicely enough observ'd You may also take notice upon the by how little the weight of the Cylinder of water upon a body immers'd in stagnant water is considerable whilst there is a pressure of collateral water to counterballance it since in this last tryal though the Cylinder of incumbent water did continually increase or decrease in length whilst the lump of Wax was sinking or emerging yet the same despicable weight of a grain or less that was just able to depress it beneath the upper surface of the water did by its pressure or removal procure its sinking to the very bottom or rising again to the top and on both occasions with an equal slowness bating that little acceleration of motion that ought to happen upon another account and which therefore is to be observ'd in the wax during its rising as well as during its sinking CHAP. IV. SOme other Phaenomena I produc'd by varying the hitherto mention'd experiment which are very favorable to our Notions about Hydrostaticks But since they do not directly concern the present Controversie I shall in this place only annex a couple the former whereof affords an easie confirmation of that Paradox which we lay as the ground of divers others and the contrary whereof is maintan'd not only by Doctor More but by many other famous and Learned men namely that in stagnant water the upper parts do actually press the lower Wee took then a very slender pipe of glass whose Cavity was narrower than that of an ordinary Goos-quill that heterogeneous Liquors may not be able to get by one another in it This Pipe near one end was bent upwards like a Syphon that it might have a short leg as Parallel as the Artificer could make it to the longer Into this crooked Pipe we put a little oyl and then held it perpendicularly in a somewhat deep and wide-mouth'd Glass fill'd partly with Water and partly with a Lump of Wax of the bigness and shape of that already mention'd that so the pressure of the incumbent Water upon the open orifice of the shorter Leg might impel the oyl into the longer Leg somewhat above the surface of the water in the Vessel which 't was convenient should be done that we might the better see the motions of the Oyl and which we knew must be done by the course we took both because Oyl is lighter in specie than Water and consequently required not an equal height of Water to counterballance it and because in very slender Pipes Water is wont to ascend a little above the Level of the External Water whereinto they are immers'd The Pipe being as was said held upright 't was easie to take notice by a mark fix'd
occasion to mention But it will clear the way for what is to follow if I here divide the noble and difficult Problem we are to consider into two Questions the first why a Diver should not be oppressed and crush'd to death by the pressure of the Incumbent and Ambient water And the second why at least he should not be made sensibly to feel it by suffering some considerable inconvenience from it In answer to the first of these Questions you will easily perceive that divers things may be pertinently applyed that you will meet with in the following Paper to shew the difference betwixt the pressure of Fluid and that of Solid bodies And that de facto the pressure of water may be exceeding great without destroying an Animal quite surrounded with that liquor I have long since shewn in another * The Author points at the Appendix to the Hydrostatical Paradoxes Treatise by the experiment of a little Tadpole which being together with the water it swam in included in a bent Glass seal'd at one end the animal was not kill'd or sensibly hurt but only according to what was lately noted by anticipation seem'd to shrink into somewhat and but little lesser dimensions If it be here alledged that this Experiment makes rather against me than for me the Learned Doctor having made use of it with a Scheme to explain it in his 16th Paragraph it will be fit for me to consider his Objection Having then recited the matter of fact newly deliver'd he adds Quod certè fieri non posset nisi juxte legem quartam contrusio particularum aquae contra se invicem Principio Hylarchico inhiberetur eluderetur Atque hinc fit ut quamvis Aqua is tubo A B C vi trudis G F aliquantò facta sit condensatior partes tamen sic compressae ut propiùs ad se invicem accedant nihilo inde inter se fiunt comprimentiores And then subjoining the following passage Neque emim sequitur ex earum contactu quod premant se invicem quandoquidem particulae uti fit in duris Corporibus in unum coalescere possunt tamen non mutuò se premere Wherein are some things that might be question'd if it were necessary He thus pursues his Discourse Cùm verò hîc particulae aquae si omninò premerent se invicem pressura in Gyrinum columnae aqueae ducentos vel trecentos pedes aeneae verò plus viginti vel triginta pedes altae pressionem adaequaret luculentum est indicium quod revera particulae se invicem non premant Nam planè est incredibile columnum aeneam pro corpore quidem gyrini latam sed altam viginti vel triginta pedes amplius Gyrinóque ad perpendiculum incumbenteâ—n omnia viscera tam tenellae Gelatinae noâ— esse elisuram Notwithstanding which allegation I am apt to think you will judge the Argument from this experiment to be more probable on my side than on the Doctors For there being in our case an animal exceedingly much more tender than a man expos'd to a pressure which he affirms is so great that if it were exercis'd on the Tadpole it ought to squeeze out all his guts I think I may pretend to have given a pertinent instance that a Diver may be at a considerable depth under water preserv'd from being crush'd to death by the weight of it And whereas the Doctor tells us that the cause of the Incolumity of the Tadpole is that the pressure or contrusion of the particles of the water against one another is hinder'd or frustrated by the Principium Hylarchicum I reply That what I affirm is matter of Fact and evident namely that there was a great external force duly and yet ineffectually applyed to press to Death by means of the water the animal swimming in it but that this Mechanical force was suspended or made ineffectual by some invisible and immaterial Agent is but the Doctors Hypothesis and a thing which whether it be true or no is at least not manifest Having said thus much about the first Question I now proceed to the second Why Divers though at never so great a depth complain not of the pressure of the water nor suffer any harm nor inconvenience by it And here Sir the Question highly meriting a particular Curiosity I shall not scruple in the more full enquiry I am now entring upon as well sometimes to employ and inlarge particulars already mentioned in the last of the following Papers as oftentimes to strengthen them with new ones And I shall also for a while suspend my difference with the Doctor and addressing my self to you who I am sure will allow me that water weighs in water propose according to my custom not as a Dogmatist but as an Inquirer some particulars that may tend to the Solution of a Problem which I take to be as difficult as noble Not that I doubt but it must and will be explicated upon the Mechanical Principles but partly because the application of them to the Solution will not offer it self to every seeker and partly because we are not yet well furnished either with experiments made on bodies under water or so much as with so competent an account of the matter of fact as I think may keep wary men from hesitations about it For what is commonly reported concerning the Divers is as has above been intimated grounded but upon their own Relations and answers perhaps amplified or procur'd by leading Questions from persons who are generally either slaves or ignorant men taken from the less sober part of the illiterate vulgar and prepossest with the common opinion of the non-gravitation of water in its own place and consequently are not like to make over-accurate observations but prone to refer the inconvenient alterations they feel to any other cause than the pressure of the water which they are taught to be none at all If observations about Diving were made by Philosophers and Mathematicians or at least intelligent men who would mind more the bringing up out of the Sea instructive observations than shipwrack'd goods we should perhaps have an account of what happens to men under water differing enough from the common reports You will in one of the following Papers find mention of a Learned Physician of my acquaintance that upon his diving leisurely perceived a constriction to be made of his Thorax by the action of the surrounding Sea-water A Spanish Prelate that liv'd long in America speaking of the deplorable condition of those wretched Indians that were employed by their inhumane Masters about the fishing for Pearls gives us this account of them * See Purch Tom. IV. Lib. 8. p. 1587. It is impossible that men should be able to live any long season under the water without taking breath the continual cold piercing them and so they dye commonly parbreaking of blood at the mouth and of the bloody flux caused by the stomach Their hair which are by
beyond its usual consistence and partly because it will not be deny'd that the corpuscles of Air may be really comprest or thrust against one another since 't is clear that they may be crouded into far less room than they possess'd before and bear so strongly against the Glasses that imprison them as not seldom if too much compress'd to burst them in pieces Consider then that among bodies not fluid the Swims of smaller fishes are likely to be judged none of the most able to resist compression since they consist of bladders so thin and delicate that a piece of fine Venice-Paper is very thick in comparison and that they contain nothing in them but soft Air not-compress'd by any outward force I caused one of these bladders of above an inch in length and proportionably great to be taken out of a Roach and anointed it with Oyl to keep it supple and preserve it from being pierced or softened by the water and having by a weight of Lead fastend to the neck of it let it down to the bottom of a hollow Cylindrical tube seal'd at one end and made purposely large and about 56 inches long for some Hydrostatical Experiments we could not perceive that by the weight of all the incumbent water it was manifestly compress'd or that it did discover the least wrinkle or other depression of the very thin membrane though stuffed but with Air. And this tryal was made more than once with the same sucess and yet that this proceeded rather from the robustness of the bladder that was able to resist the weight of a taller pillar of water than from the Non-gravitation of water in the upper part of the tube on that in the lower we shew'd by presently letting down such a Mercurial-Gage as is describ'd often mentioned in the Continuation of our New Experiments For letting down this by a string to the bottom of a tube the weight of the incumbent water forced up some of the Mercury out of the open leg of the Syphon into the seal'd one and consequently compress'd the air included there which though it were not very much yet it was very manifest For the uncompress'd Air being 3 inches and â… in length we judg'd it at the bottom of the tube about â… by the intrusion of the Mercury that was impell'd up and to satisfie my self and others that if the incumbent water had been heavy enough it would have visibly depress'd the bladder in spite of any Principium Hylarchicum since I could not have a tube long enough the bladder was sunk into a Chrystal-Glass that had a long and Cylindrical neck and was so well stuffed with a stopple that was Cylindrical too that 't was very difficult for any thing to get out betwixt it and the orifice of the Glass then a competent Quantity of air being left above the water the stopple was warily and by degrees thrust down and so lessening the capacity of the Glass compress'd the air that was next it and by the intervention of that the water that was under it And though there did not upon a slight compression of the outward air appear any sensible operation upon the bladder that was at the bottom of the water yet upon a farther intrusion of the stopple the pressure being encreas'd the immers'd bladder discover'd not only one but two considerably deep wrinkles which presently disappear'd upon the drawing up of the stopple Upon whose being thrust in again depressions were again to be seen on the Swim And we having been careful to conveigh into the same Glass such a Mercurial Gage as has been lately spoken of we estimated by the condensation of the air in the seal'd leg of that Gage that the bladder had been expos'd to a pressure that might be equivalent to that of a pillar of about 40 foot of water This I hope will lessen the wonder that Bodies of so firm a texture as those of lusty men should support the pressure of the water at such depths as Divers are wont to stay at since we see what resistance can be made by so exceeding thin and delicate a membrane stuff'd only with air in comparison of the strong membrans and fibres of a man stuff'd besides Air with more firm parts I will not here urge that great weights may be sustain'd in the Air by such tendons or cords of fibres and by other fibres as it were interwoven into membrans in comparison of what an ordinary man would expect But I shall invite you to consider with me that not only upon the account of the stable parts of the humane Body but of the Spirits too it may resist very violent pressures and such as perhaps have not yet been considered of a fluid Body not only without any manifest conrusion or dislocation of parts but without any sense of pain which I suppose you will grant me if considering what great effects Gusts of Wind have upon Dores Trees nay Masts of Ships blowing them down nay breaking them and that yet a man without being extraordinary strong will stand against the impetuosity of such a strong Wind and walk directly against it by vertue of the vigour of his muscles and spirits without being thrown down or bruis'd by so violent a Current of Air as beats upon him but without so much as complaining that he feels any pain and this though the Wind that beats against him however it be a fluid Body yet because it acts as a stream does not uniformly compress him but invade only the fore-part of his Body Likewise in the lifting up heavy weights by Porters Carriers and other lusty men we may see the slender tendons of the hands loaded with 100 or 150 or perhaps a far greater number of pounds without having their fibres so far compress'd or stretch'd as to make the lifters complain of pain though sometimes they may of difficulty So that as I could if it were needful confirm by other Instances a humane Body is an Engine of a much firmer structure than Scholars are wont to take notice of And here let me add that I doubt whether if the structure of a man were not considerably though not perhaps equally firm he would especially in a deep Sea be able to bear the pressure of the water though not immediately applyed without pain For to give you one Reason more of my not acquiescing in vulgar reports about Diving having several times convers'd with a man apt enough both to enquire and observe who got his living by taking up Shipwrack'd goods he answer'd me when I ask'd him whether he felt any peculine pressure against the Drums of his Ears which are membranes â—â—t so well back'd as those of other parts that when he stai'd at a considerable depth as 10 or 12 fathoms under the surface of the Sea he felt a great pain in both his ears which often put him to shifts to lessen it which by his manner of describing it I concluded was from
since had the Curiosity to try in a very deep part of the Sea whether any fresh Water would strain into Stone-bottles through a thick Cork strongly stopt in and having let it down with a convenient weight to 100 fathom was much disappointed when he drew it up by finding that the pressure of the Water at so vast a depth had quite thrust down the Cork into the Cavity of the bottle which else perhaps would have been crushed to pieces an effect which he would scarce have expected from the stroaks of a Mallet And if to all this it be objected that 't was not the pressure but the coldness of the Water that did the recited feats by condensing the included Air and obliging Nature to do the rest for fear of a Vacuum I will not lanch into the Controversie whether Nature do any thing ob fugam Vacui but only answer that I cannot find by the Relations of the Divers or otherwise that 't is ever so cold at the bottom of the Sea as 't is frequently above ground in Winter when great Fishes are commonly said to return to the deep parts of the Sea for warmth and yet in the sharpest Winters I never observ'd Corks to be driven in by the cold of the Ambient nay I purposely tryed with a Frigorifick mixture that very intense degrees of cold such as would quickly freez many Liquors would not occasion the breaking of thin bubbles of Glass purposely blown at the flame of a Lamp and hermetically sealed And to shew ad oculum as they speak that Water may press more and more as it grows deeper against the stopple of a Bottle though the Vessel be inverted I will subjoyn this Experiment Because we have no Water hereabouts that is near deep enough to force in a Cork as the Sea-water did in the above recited tryals I thought of a way of so closing the Glass-vessel as that the stopple should keep asunder the Air in the Vessel and the outward Water and hinder all immediate intercourse between them and also make some resistance against the pressure of the external Water and yet be capable of freely moving up and down and so be a good Succedaneum to a solid stopple Taking then a Glass-Vial furnished with a somewhat long Cylindrical neck whose Cavity was large in proportion to the rest of the Vessel we put into it as much Quicksilver as would in the neck make a short Mercurial Pillar of between half an inch and an inch then a piece of very fine Bladder dipp'd in Oil was so tyed over the orifice of the Glass that no Mercury could fall down or get out nor Water get in at the orifice and yet the Bladder by reason of its great limberness might be easily thrust up towards the Cavity of the Vial or depress'd by the weight of the Mercury This little instrument first furnished with a weight of Lead to sink it being inverted the Mercury descended into the neck and closed the orifice as exactly as a stopple and yet with its lower part depress'd the Bladder beneath the Horizontal Plane that might be conceiv'd to pass by the orifice then the Glass being a while kept in the Water that the included Air might be brought to the Temperature of the surrounding Liquor and by a string let further down into the same Glass-vessel fill'd to about two foot in height the pressure of the Liquor against the orifice of the Vial did by degrees drive up the Bladder and the Mercurial stopple into the cavity of the Neck as was manifest by the ascension of the Quicksilver and when the instrument was leisurely drawn up again the weight of this Mercury made it subside and plump up the Bladder again as before An Experiment akin to this and therefore fit to confirm it I have deliver'd in another * See the Paradox about Suction Discourse And here I shall subjoyn what very opportunely occurr'd to me since the writing of the last page Meeting casually with an Ingenious Mechanician whom you will find I have * In the Tract of the Differing Pressure of heavy Solids and Fluids elsewhere mentioned that devised a suit of cloaths and other accommodations wherein I once saw him let down into the Water by whose help and that of a boat he could and did continue there a great while at a considerable depth under water and there work I ask'd him afresh to obtain fuller informations than formerly whether he felt not the pressure of the water against his breast and belly to which he answer'd me more circumstantially than he had before that when he was about 4 or 5 yards under water though but in the River Thames his breast and abdomen was so comprest that there being hardly room enough left for the free motion of his Lungs he could scarce fetch his breath and was necessitated to make them draw him quickly up and that among his later tryals to improve his Engine having for remedy hereof caused a kind of Armour for the Chest and back to be made of Copper though the stiffness of the Metal defended him from receiving any mischief in those parts yet in the others where only the Leather though strong was interposed when he came to the depth of about six fathom though in fresh water he found a great pressure against his legs and armes and all the other parts against which the water was able to thrust the Leathern suit inwards And this pressure being found by him as he told me pretty equal against all the exposed parts for from the other which were more yielding and obnoxious the Armour kept it off he received no Mischief from it not yet much Incommodity and some he might expect from the stiffness and unequal yielding of the Leather so that he could stay under water though not still at so great a depth about 2 hours or longer And upon the whole matter he answered me that he was well satisfied by his tryals that the ambient water endeavoured to press him his Diving suit every way inwards Whether the coldness of the water had any interest in this Phaenomenon I particularly enquired of the Engineer but he replyed that by reasion of the tightness of his Diving suit or instrument the warm steams of his body that were pent in and other concurring circumstances kept him from feeling any cold and made him sometimes feel a greater Heat than he wished He has promised me before it be very long to make for me a tryal or two that I propounded to him from whose success if he can but reduce them to Experiment I hope to be able to present you a farther Confirmation of our Hypothesis In the mean time the things already recited together with the preceeding Experiments may well suffice for our present purpose For by what hath been said it appears that Water does actually press against bodies whether specifically lighter or heavier than it self placed under water and that this pressure
increases with the height of the water above the immersed Bodies And this being so it is not more necessary for me than for men of other Opinions to give a clear reason why Divers can resist so great a pressure of the incumbent water And the pressure of the water in our recited Experiment having manifest effects upon Inanimate bodies which are not capable of prepossessions or giving us partial informations will have much more weight with unprojudiced persons than the suspicious and sometimes disagreeing accounts of ignorant Divers whom prejudicate opinions may much sway and whose very sensations as those of other vulgar men may be influenced by Predispositions and so many other Circumstances that they may easily give occasion to mistakes I know that Learned men that never were conversant in Hydrostaticks are wont to think it very difficult if not impossible to conceive how so weak a thing as they fancy an Animal to be should avoid the being oppress'd or so much as harmed by so great a weight of Water But they that shall attentively consider what has been offer'd towards the removal of this difficulty and remember how little they would have believed that there is so great a difference as we have by the Tadpole the Fly and other instances shewn there really is between the pressure of Solid and of Fluid bodies will I presume be apt to think it fit that if for want of a sufficient History of matters of fact any scruple remain about the Solution we have offer'd from the nature of the Uniform pressure of Fluids and the Firm structure of the Humane body we should to remove those remaining scruples also rather range about for other Physical helps to solve more compleatly the Problem about such a thing as Compression which is an action purely Corporeal and Mechanical than for want of a ready and compleat Solution to flye to the immediate interposition of an immaterial and intelligent yet Created Agent to explain clearly whose manner of working would be a much more difficult Task than the solution of the Phaenomenon without it And now Sir having presented to you the Reflections I thought requisite to write upon the Learned Doctors discourses against my Hypothesis and Explications relating to the gravitation and pressure of Fluids I have little more to trouble you with in this Paper For though in the latter part of the 13th Chapter the Doctor is pleased to spend divers pages in the Explication of divers of my Hydrostatical Phaenomena by the Agency of that incorporeal Director that he calls Principium Hylarchicum yet since these Explications of his are rather attempts to accommodate the Phaenomena to the Hypothesis than objections directly levell'd against my Solutions I shall altogether forbear to examine them the main thing that I intended in this Paper according to what I told you at the beginning being to shew that the Arguments urg'd against the Mechanical solutions of the Experiments by me recited do not evince any of them to be erroneous And I have neither the design nor the leasure solicitously to examine the Doctors Hylarchical Principle Of which I shall only say that though he tells us it is * Page 175. paratum ad movendum quoquoversum materiam pro data occasione yet since he also tells us * Page 167. Quod particulae molis corporeae sive stabilis sive fluidae à Principio Hylarchico in unam aliquam partem omnes junctim urgeri possunt premi quamvis singulae singulas in nullam partem premant quodque pro magnitudine molis major minorve totius fit pressio and that the force by which it endeavours to keep the Elements in their true and natural Consistence though it be very great is not invincible * Pag. 167. I see no need we have to flye to it since such Mechanical Affections of matter as the Spring and Weight of the Air the Gravity and Fluidity of the water and other Liquors may suffice to produce and account for the Phaenomena without recourse to an Incorporeal Creature which 't is like the Peripateticks and divers other Philosophers may think less qualified for the Province assign'd it than their fuga Vacui whereto they ascribe an Unlimited power to execute its Functions I leave it therefore to you Sir to judge which of the two ways of explicating an Hydrostatical Phaenomenon the Learned Doctors or that which I have made use of relishes most of the Naturalist And I shall only tell you that if I had been with those Jesuites that are said to have presented the first watch to the King of China who took it to be a living Creature I should have thought I had fairly accounted for it if by the shape size motion c. of the Spring-wheels balance and other parts of the watch I had shewn that an Engine of such a structure would necessarily mark the hours though I could not have brought an argument to convince the Chinese-Monarch that it was not endowed with Life From which comparison you will easily gather that what I have thought my self concern'd to doe in this place was not to demonstrate in general that there can be no such thing as the Learned Doctors Principium Hylarchicum but only to intimate that whether there be or not our Hydrostaticks do not need it Nor do I think it necessary to the Doctors grand and laudable design wherein I heartily wish him much success of proving the existence of an Incorporeal substance For as I think Truth ought to be pleaded for only by Truth so I take that which the Doctor contends for to be evincible in the rightest way of proceeding by a person of far less learning than He without introducing any precarious Principle especially experience having shewn that the generality of Heathen Philosophers were convinc'd of the being of a divine Architect of the World by the contemplation of so vast and admirably contriv'd a Fabrick wherein yet taking no notice of an immaterial Principium Hylarchicum they believed things to be managed in a meer Physical way according to the General Laws setled among things Corporeal acting upon one another And after this I have nothing more to say but that I would not have any thing that I have said misconstrued to the Learned Doctors prejudice For 't is nor necessary that a great Scholar should be a good Hydrostatician And a few hallucinations about a subject to which the greatest Clerks have been generally such strangers may warrant us to dissent from his opinion without obliging us to be enemies to his Reputation And therefore if you have found any thing in this Paper inconsistent with a just tenderness of that you have not only my consent but my desire to alter it as an Expression that doth not well comply with my Intentions of not appearing any farther his Adversary in our Debate than the desire of shewing my self a Friend to the Truth I was to defend should exact of SIR Your
c. An Hydrostatical LETTER Written Feb. 13. 167 2 3 Containing a Dilucidation of an Experiment of the Honourable Author of these Tracts about a Way of Weighing Water in Water upon the occasion of some Exceptions made to it by Mr. George Sinclaer * In his Hydrostaticks printed at Edenburg 1672. p. 146. ss TO THE READER WHen this Discourse was just finishing in the Press there came to the Publisher's hands a dilucidation of an Experiment of the Honourable Author of these Tracts about a Contrivance of his for Estimating the Weight of Water in Water formerly publisht in Numb 50. of the Philosoph Transactions and by the following Discourse clear'd from the exceptions to be met with in Mr. George Sinclair's Book entitl'd The Hydrostaticks c. printed at Edenburg 1672. Which Dilucidation because of the Affinity of the subject was thought fit to be here annext An Hydrostatical LETTER Written Feb. 13. 1672 3. Containing a Dilucidation of an Experiment of the Honourable Author of these Tracts about a Way of Weighing Water in Water upon the occasion of some Exceptions made to it by Mr. George Sinclair * In his Hydrostaticks printed at Edenburg 1672. p. 146. ss SIR CAlling this night in Pauls Church-yard for the Ingenious Mr. Rays Travels that you yesterday commended to me I was also shewn a New Treatise that I never saw before of a Learned Gentleman and hastily running over the Index found an Experiment of mine declared Insufficient and though being hinder'd to make hast home it be so late that far from having time to peruse the book it self which I tell you that you may not now expect any Character of it from me I have been scarce able to read over more than once what directly concerns me in it yet I shall adventure to say something about it this night for fear I should not in so busie a time as this be allowed to do it to morrow Whereas then the Learned Objector having recited my experiment about weighing Water in Water as you were pleased to publish it in a book enriched with so many better things the * Numb 50. Philosophical Transactions begins his animadversion with saying that herein is a great mistake I shall not in that much oppose him For possibly the Dispute between us is not much more than verbal And because my Experiment coming abroad by it self and supposing things that I had formerly proved and published but which were not expresly referr'd to in it I wonder not that my meaning should not by all Readers be fully understood And therefore to explain my self on this occasion give me leave both to repeat my Opinion and to shew you on what occasion and how far I design'd to confirm it by this Experiment My opinion then was and still is that as water is a heavy fluid so it does retain its Gravitation and power of pressing by which I mean a tendency downwards whatever the cause of that gravity be whether it have under it a body either specifically heavier or lighter than it self or equiponderant to it For I see not what should destroy or abolish this Gravity though many things may hinder some effects of it And therefore I suppose that Water retains its Gravity not only in Air but in Water too and in heavier liquors and consequently by vertue of this the liquor presses upon them but if a surrounding fluid have upon the score of its specifick Gravity an equal or a stronger tendency downwards than water it will by vertue of that be able to impel up this liquor or to keep it from actually descending so that a portion of water supposed to be included in a Vessel of the same specifick weight with water this portion I say placed in a greater Quantity of the same water will neither rise nor fall as I have elsewhere shewn but yet it retains its Gravity there only this Gravity is kept from making it actually descend by the contrary action of the other water whose specifick Gravity is supposed equal as when a just ballance is loaded with a pound weight in each of its scales though neither of the weights actually descend being hinder'd by its counterpoise yet each retains its whole weight and with it presses the scale it leans upon so that our lately mentioned included portion of water does really press the subjacent water though it does not actually depress it or as perhaps a School-man would phrase it does gravitate on it but not pregravitate Nor do I think that the only way of judging whether a body gravitates is to observe whether it actually descends since in many cases its Gravity may be proved by the Resistance it makes to heavy bodies which if it were not one would raise it As may be declar'd by what I just now noted about equal weights in a ballance And for want of this distinction I have known even learned men treating of Hydrostatical things mistake both me and the Question The next thing I had to tell you is that the Adversaries I had to deal with both in Print and in Discourse denyed that in standing Water the upper parts did press or gravitate upon the lower and though they could not but grant that the whole weight of the Water did gravitate upon the bottom of the Vessel yet they would have the parts of it to do so actione communi as they speak and fancied I know not what power of Nature to keep the homogeneous portions of Water as well as other Elements from pressing one another when it is in its proper place Against this Opinion which I presume my Learned Adversary and I agree in opposing it was alledged besides other things which I found many otherwise good Scholars were not fitted to understand That if a Glass-vial or bottle well stopt were deeply immersed under water it would strongly tend upwards but if it were dextrously unstop'd when 't was thus immers'd so as the water could get in abstracting from or allowing for the weight of the Glass it self 't would by the water that crouds in and thrusts out the Air be made strongly to tend downwards and continue sunk But this not satisfying because 't was pretended that the reason of the empty bottles emerging when stopt was the positive Levity of the Air it was filled with and the sinking of it when unstopt was from the recess of the same Air that by the intruding Water was driven with large bubbles out of the bottle I thought this evasion might be obviated by contriving an Experiment wherein the Water should be plentifully and suddenly admitted into the Glass and yet no Air expelled out of it which Circumstance I therefore took notice of where I say no bubble of Air appear'd to emerge or escape through the water so that if then the Glass that was kept up before should fall to the bottom with a gravitation amounting to a considerable weight in respect of its capacity the sinking of it
the Gravity of the VVater and not upon the positive Levity of the Air. FINIS NEW EXPERIMENTS Of the Positive or Relative LEVITY of BODIES Under Water NEW EXPERIMENTS Of the Positive or Relative Levity of Bodies under Water 'T Is obvious even to the Vulgar as well as to Philosophers that if Wood Wax or another body that is lighter in specie than water and naturally floats upon it be detained under water it will upon removal of that force emerge to the top And this it does so readily and as it seems spontaneously that not only the Peripatetick Schools but the generality of Philosophers both ancient and modern do as well as the Vulgar ascribe this ascention of lighter bodies in water to an internal principle which they therefore call Positive Levity But this Principle was not always so universally receiv'd among Philosophers as in later ages it proved to be Democritus and several of the Antients both Atomists and others admitting no absolute but only a relative or respective Levity which opinion some of the Moderns have ingeniously attempted to revive But because whatever wit they may have imploy'd in arguing yet the Schools seem to have the advantage in point of Experience the obvious instances given by the Peripateticks having neither been solv'd by real and practical variations of the same instances nor counterballanc'd by new Experiments of a contrary tendency the importance and difficulty of the subject invited me to attempt when I was upon Hydrostatical tryals whether I could experimentally shew that whatever becomes of the general Question about Positive Levity we need not admit it for the true and adaequate cause of the emersion of Wood and such lighter bodies let go under water EXPER. I. THe instance that is wont to be urg'd to prove the Positive Levity of Wood in Water seems to me to have been too perfunctorily made to be safely acquiesced in For even as it is propos'd with advantage by a learned forreign Mathematician I cannot think it accurate enough to determine the present Controversie for I will readily allow him to suppose that in case a flat board as for instance a Trencher have its broad surface kept by a mans hand or other competent force upon the Horizontal bottom of a Tub full of water if the hand or other body that detain'd it be remov'd it will ordinarily happen that the Trencher will hastily ascend to the surface of the water But I do not perceive that a decisive Experiment of this kind is easie not to say possible to be made with such materials For the wood whereof both the Trencher and the bottom of the Barrel consist are suppos'd to be lighter in specie than Water and to be so they must be of a porous and not very close texture To which agrees very well that the solider woods as Lignum Vitae Brasil c. whose texture is more close and compact will not float on water but sink in it And therefore if there be not much more care us'd than I have yet heard that any Experimenter has imploy'd to bring the surfaces of the Trencher and the bottom of the Barrel to a true flatness and as much smoothness as they can be brought to I shall not think the tryal so accurately made as it might be not to say which I suspect that though it be mentally yet it is scarce practically possible to bring such porous bodies as those of the lighter woods to be fit for such a contact as might be necessary to make the tryal accurately And in case that were actually done I should be kept from expecting with my adversaries the emersion of the Trencher by the Experiment by and by to be recited and by the true reason of it I think then that the cause why in ordinary instances Wood Wax and other bodies specifically lighter than water being let go at the bottom of a vessel full of that liquor emerge to the top is chiefly that there is no such exquisite congruity and contact between the lowermost superficies of the Wood and the upper surface of the bottom of the Vessel but that the lateral parts of the Water being impell'd by the weight of the parts of the same liquor incumbent on them are made to insinuate and get between the lower parts of the Wood and the bottom of the Vessel and so lift or thrust upwards the Wood which bulk for bulk is less heavy than the Water that extrudes it That this is the reason of the Emersion or ascension of bodies lighter in specie than the fluids they swim in is most consonant to the Laws of * See the Hydrostatical Paradoxes Hydrostaticks as I have elsewhere shown But whereas the whole force of the argument of those I dispute with consists in a supposition that because the Trencher formerly spoken of is plac'd upon the bottom of the Barrel no water can come between to buoy it up whence they conclude it must ascend by an internal and positive principle of Levity I thought fit to make the Experiment after another and if I mistake not a better manner We took then two round plates of Black Marble shap'd like Cheeses which had those superficies that were to be clap'd together ground very flat and polish'd very carefully that the stones being laid one upon the other might touch in as many of the superficial parts as the workman could bring them to do that whilst they were in that position the uppermost being taken up the other would stick to it and ascend with it And to keep out the water the better the internal surfaces were before they were put together lightly and but very lightly oyl'd which did not hinder them from most easily sliding along one another either forward or backwards or to the right or to the left as long as the contiguous surfaces were kept Horizontal These things being done a blown Bladder of a moderate size was fastned to the upper marble and both of them were let down to the bottom of a tub of water where by the help of an easie contrivance the lower marble was kept level to the Horizon And now the Patrons of Positive Levity would have concluded that the bladder being a body granted to be by vast odds lighter than wood and being in an unnatural place beneath the surface of the water should of its own accord and with impetuosity emerge but I expected a contrary event because the bladder being tied to the upper marble so that both of them might in our case be considered as one body the water could not impel them up in regard that the close contact of the surfaces of the two marbles kept the water from being able to insinuate it self between them and consequently from getting underneath the upper marble and pressing against the lower superficies of it And to shew that this was the reason of the bladders not emerging I caus'd one of the by-standers to thrust his arm down to the bottom of the
tub and with his hand to make part of the oyl'd surface of the upper marble slide off on any side from that of the lower which by reason of the smoothness and slipperiness of the surfaces he found most easie to do But the contact still continuing according to a greater part of the surfaces than was requisite I bid him yet slide but by slow degrees more and more of the upper marbles from the lower till at length when according to his guess the marbles touch'd but in one half of their surfaces the endeavour of the water to extrude the bladder full of Air being stronger than the resistance which the contact but of part of the surfaces of the stones was able to make they were suddenly dis-joyn'd and the bladder was by the extruding water impetuously as it were shot up not only to the top of the water but a good way beyond it With these Marbles we made several other Experiments of this kind most commonly letting down the Marbles both together but once or twice at least placing the upper Marble under water upon the lowermost already fixed to the bottom of the barrel That 't was not the weight of the upper Marble nor want of Lightness whether positive or relative of the Air included in the bladder that kept it from ascending was plain not only by the newly mention'd impetuous emersion of it upon the dis-joyning of the Marbles but by this that the Bladder would lift up from the lower parts of the water not only the upper stone when it touch'd not the other but a weight of seven or eight pound hanging at it And that a Fuga Vacui was not an adequate cause of the cohesion of the Marbles in our Experiment may be argued from this that whether or no nature do any thing at any time out of abhorrence of a Vacuum which may be much disputed yet in our case this abhorrency could not be well pleaded by its Assertors since many of them hold it to be unlimited and the more modest to be at least capable of lifting up prodigious weights whereas in our Experiment the Levity of a Bladder that could not raise ten pound weight was sufficient to disjoyn the marbles when they yet touch'd one another according to half their surfaces EXPER. II. TO shew now whether it is not rather the Gravity and Pressure of the Water or other ambient fluid than the Positive Levity of a body lighter in specie than it that makes the immers'd body ascend to the surface of the liquor I devis'd this Experiment We took a bladder out of which a great part of the included Air had been express'd and tying the neck of it very close that none of the remaining Air might get out we fastned to it a considerable weight of some very ponderous body as Lead or Iron By the help of this we sunk the bladder to the bottom of a wide mouth'd glass full of water that the surface of the liquor might be a good deal higher than the upper part of the bladder This wide mouth'd glass we included in a great Receiver whose orifice must be very large to be able to admit such a vessel which I caus'd to be carefully cemented on to the Engine The main scope of this Experiment was to shew that though the Air included in the bladder was very far from being able by its absolute levity to lift up so great a weight as the bladder was clog'd with yet the same Air continually included in the bladder would by its meer expansion without any new external heat acquire a power of ascending in spite of that weight which ascension therefore must be attributed to the water which according to the Laws Hydrostatical ought caeterisparibus to resist or buoy up more potently those immersed bodies that being lighter in specie than it possess the greatest place in it and hinder the more water from acquiring its due situation as we see that among hollow spheres of glass and metal equally thick and well stopp'd there is a much heavier weight requisite to sink a large one than a small one For the prosecution of this tryal we began to pump the Air out of the great Receiver and its pressure upon the surface of the water being thereby more and more lessen'd according to what we elsewhere more fully declare the spring of the included Air began by degrees to distend the sides of the bladder till at length that vessel of Air swelling every way took up so much more room in the water than it did before that the water was able to lift the bladder and the annexed weight to the top and detain it there till we thought fit to let in again some of the excluded Air which forcing that in the bladder to shrink in its dimensions the weight was presently able to sink it to the bottom And here it may be noted that if instead of hanging so great a weight at the neck of the bladder we fastned but a moderately heavy piece of Lead such as would only serve to sink the bladder and keep it at the bottom of the water so that the aggregate of the Bladder Air and Metal was but a little heavier than a bulk of water equal to them Then upon the first suck or operation of the Pump which could withdraw but a small part of the Air in the Receiver the Air in the bladder suddenly expanding it self would forthwith be impetuously extruded by the water though after some reciprocations it would float in its due position till upon the return of a little outward air sometimes as little as we could conveniently let in it would immediately subside But this is not so necessary to be insisted on as 't is to take notice that I foresaw it may be objected that the ascension of the weight was not effected by the pressure of the water but by this that Rarity and Levity being Qualities exceedingly of kinn the great Rarefaction of the Air might proportionably increase the Levity of it and consequently enable it to perform much greater things than it could do before I will not here dispute whether generally speaking a body rarified without heat would in Vacuo or in a fluid not heavier in specie than the body when rarified meerly by such a greater distance of its parts as may suffice to entitle it to rarefaction become really heavier or lighter than before I will not I say discuss this question here where it may serve my turn to satisfie the recited objection by the following Experiment EXPER. III. ABout the neck of a conveniently shap'd Viol capable to hold some few ounces of water I caus'd to be carefully tied the neck of a small Bladder whence the Air had been diligently express'd so that the Bladder being very limber of it self and probably made more so as well as more impervious to Air and Water by the fine Oyl we had caus'd it to be rubb'd with lay upon the orifice
of the Viol like a skin clapp'd together with many folds and wrinkles This done we let down the Viol into a conveniently shap'd Vessel full of water and the Viol being poysed before-hand for that purpose sunk perpendicularly in the liquor till the neck of the Glass was partly above and partly beneath the surface of the water Then covering the external Glass with a large Receiver we caus'd the Air to be pump'd out and as the pressure of that was gradually withdrawn the Air in the floating Viol did little by little expand it self into the Bladder and unfolded the winkles of it till at length it became full blown without altering the erected posture of the Glass it lean'd upon But this great expansion being made above the Water and consequently in a medium not heavier than the included Air gave that highly rarified Air no such increase of Levity as enabled us to perceive that it made so much as the neck of the Glass arise higher in the Water than it did before Nor did we take notice that the return of the Air into the Receiver by reducing the Air in the Bladder to its former unrarify'd estate made the Glass sink deeper than before But when the Experiment was tryed with the same Glass and Bladder at the bottom of the Water then upon the pumping out the Air the Bladder being dilated under water was after a while carried up to the top and took up with it about eight or ten ounces that had been to clog it fasten'd to the bottom of the Viol. NEW EXPERIMENTS About the PRESSURE of the AIR' 's SPRING On Bodies under Water NEW EXPERIMENTS About the Pressure of the Air 's Spring on Bodies under Water I Do not think it were difficult for an intelligent peruser of our Physico-Mechanical Experiments to find there divers Phaenomena whence it may be deduc'd that Bodies under water though kept by that liquor from the immediate contact of the Air may yet be expos'd to its pressure whether the Air act as having a Weight or as a Spring But because not only the Vulgar but Philosophers have been so long and generally possess'd with an opinion that a fluid so little heavy as the Air cannot by its weight act upon a liquor that is like water bulk for bulk a thousand times heavier than it And because also it seems yet more strange that a little Air perhaps not amounting to a scruple or drachm in weight should in its ordinary state of Laxity act considerably upon Bodies which being cover'd with water seem by the interposition of that liquor to be fenced from the incumbent Air it may be worth while to add three or four Hydrostatical Experiments to confirm a Truth that very few are yet acquainted with and add to the proofs already given of the power of the Spring of the Air some of the operations we have discovered it to have upon Bodies plac'd under water There are two sorts of Tryals that I shall imploy to shew that a small quantity of inclosed Air may by its pressure which in our cases must depend upon its Spring have a considerable operation upon bodies under water notwithstanding the interposition of that liquor For this pressure we speak of may be manifested in the first place by what it directly and positively operates upon bodies covered with water And in the next place by the things that regularly ensue upon the removal of the inclos'd Air or the weakning of its Spring EXPER. I. TO begin with the former way of shewing the pressure of the Air I thought it sufficient in regard of the Tryals to be referr'd to the second way to make the following Experiment We took a square Glass-Viol guess'd to be capable of holding between half a pint and a pint of water the neck of this we luted on carefully and strongly for else it would have been buoy'd up over the orifice of the small pipe at which the Air passes in our Engine out of the Receiver into the Pump Then whelming over this glass a great Receiver we luted it strongly to the Engine that it might as well keep in the Water as keep out the Air and at the top poured in as much water as sufficed to inviron the internal Receiver if I may so call it and cover it to a pretty height This done we exactly closed with a turning key the holâ— in the great Receiver at which the water had been poured in that no air might get in or out that way And lastly we began to pump out the Air contain'd in the internal Receiver to the end that that Air which by the above-mention'd pipe had Communication with the External Air might no longer by its pressure assist the glass to resist the pressure which the incumbent and inclos'd Air by vertue of its Spring constantly exercises upon the subjacent water and by its intervention upon the sides and bottom of the internal Receiver And as we expected not that this glass by its own single force should resist the pressure of the Air inclos'd in the upper part of the great Receiver notwithstanding the interposition of the water so the event fully justified our conjecture For at the first exuction which could not be suppos'd to have well emptied the internal glass this vessel was by the pressure of the superior Air upon the circumstant water broken into I know not how many pieces And the same Experiment though with a little slower success was repeated with a stronger internal glass EXPER. II. I Proceed now to the second way of manifesting the pressure of inclos'd Air upon Bodies under water which is by shewing the Phaenomena exhibited by those Bodies upon the removal or lessening of that pressure Having squeez'd out of a moderately sized Bladder the greatest part of its Air we tied the neck of it very close and then fastning to it a competent weight we plac'd it at the bottom of the tallest and largest glass we could cover with our great Receiver that so though the incumbent Air were pump'd out none of the Water might be pump'd out with it but still retain the same height above the Bladder Having then poured upon the Bladder as much Water as would swim a great way above the upper part of it we cover'd this glass of Water with a great Receiver which being carefully cemented on to the Engine the Pump was set a-work and as the Air which by its Spring press'd upon the surface of the included Water was by degrees pump'd out so the Air that was imprison'd in the Bladder did gradually expand it self at the bottom of the Water as if no such liquor had interpos'd between them otherwise than by its weight upon whose account it must be allowed to give some little impediment to the expansion of the Bladder in proportion to the height it had above it The Event of our Experiment was such as was expected namely that the immers'd Bladder was at length full blown by the
dilatation of the Air inclos'd in it and by its intumescence made a considerable part of the Water run over by the sides of the glass that before contained it all And when access was given again to the external Air the internal being compressed the Bladder was presently reduc'd to its wrinkled state EXPER. III. WE took a small but fine Bladder whose neck was strongly tied up when it was by guess about half full of Air This we put into a short brass Cylinder the lower of whose bases was clos'd with a Brass-plate and the other left open this open orifice we afterwards stop'd but not exactly with a Cylindrical plugg that was somewhat less wide than it and was by a rim at the top hinder'd from reaching too deep into the cavity of the Cylinder that it might not do mischief to the Bladder that lay there beneath it upon this plugg we plac'd an almost Conically shap'd weight of Lead and this pile of several things being so plac'd upon our Engine that we could cover it with a great Receiver we carefully cemented on this vessel and at the top of it poured in so much water as would serve to fill the vacant part of the brass Cylinder and the cavity of the Engine to such a height that it cover'd all the leaden weâ—ght which was several inches high except a rim which was fastned to the top of it for the convenienter removing of it All this being done the Pump was set a-work and long before we had exhausted the Air of the Receiver that which was inclos'd in the lank bladder had by degrees display'd so vigorous a spring that it had heav'd up the weight that lay upon it to a notable height and kept it there till the Air was let in from without to assist its being depress'd by the leaden weight which amounted to no less than about 28. pound EXPER. IV. THere remain'd yet one tryal to be made which in case it should succeed seem'd likely to appear as great an evidence of the force of the Air 's Spring upon bodies under water as could be reasonably desired of us it having been look'd upon by many Virtuosi as the considerablest instance of the force of the Air 's Spring even when no water interven'd in the tryal To satisfie therefore our curiosity we took a copper Vessel of a Cylindrical shape and a considerable height into this being first almost filled with water we put a square Glass-Vial capable by guess to hold nine or ten ounces of water and exactly stop'd with a cork and a close Cement this Vial by a competent weight was detain'd at the bottom of the water from whose upper surface it was considerably distant then the Copper Vessel being plac'd upon the Engine and included in a great Receiver well cemented on the Air was by degrees pump'd out but before it was quite exhausted the Glass at the bottom of the water was by the spring of the Air included in it burst into many pieces not without great noise and a kind of smoak or mist that appear'd above the surface of the water Another Glass of the same sort had been broken after the same manner in another Vessel but having afforded us no particular Phaenomenon I barely mention it to shew that we made more than one tryal of this kind The consequence that will naturally result from the three last Experiments is this that since barely upon the withdrawing of the pressure of the included Air which was perhaps but very little in quantity the Air residing in the immers'd bodies did by vertue of its Spring expand it self so forcibly as we have recited and perform notable things the Air above the Water must have exercis'd a very powerful pressure upon the surface of it since setting aside the weight of the water of small moment in our tryals it must have been at least aequivalent to and probably much exceeded that force of the immers'd Air whose exercise it was able totally to hinder And from hence it may be easily deduc'd that the weight of the Atmosphere acts upon bodies under water notwithstanding that the interpos'd liquor is by vast odds heavier in specie than Air for we have just now prov'd the pressure of inclos'd Air which consists in its Spring upon bodies under water and 't is manifest that the strength of the Spring of this inferiour Air we make our tryals with is caus'd by the weight of the superiour Air which bends and compresses those little Aereal springy particles whereof our Air consists so that the weight of the Atmosphere being aequivalent to the Spring of the inferiour Air for else it could not compress it as much as it does must lean upon the surface of the subjacent water with a force aequivalent to the spring of that part of it that is contiguous to the water This Experiment brings into my mind another that I once made which though not properly Hydrostatical yet relating to positive Levity may perhaps be not uselesly added on this occasion wherefore I shall here subjoyn a transcript of the Phaenomenon that belongs to our present purpose as 't is registred soon after the Experiment was made To examine by a visible Experiment the common doctrine that a portion of Air by being much dilated rarified or expanded does acquire a new and proportionable degree of Positive Levity I devis'd to put in practice the following way We took a Bladder of a moderate size that was very fine and limber that it might be the lighter and more easily distended The most part of the Air being squeez'd out of the Bladder the neck of it was tied up very close that no air might get out of it nor any external get into it This limber Bladder was hung at one of the Scales of a Ballance whose Beam had been purposely made more than ordinarily short that the instrument which yet was ticklish enough might be suspended and capable of playing in the cavity of a great Receiver into which we conveyed it having first carefully counterpoysed the Bladder with a metalline weight put into the opposite scale This done the Air was pump'd out and as that was withdrawn the Bladder was more and more expanded by the Spring of the internal Air till at length when the Receiver was well exhausted it appear'd to be quite full Notwithstanding which great dilatation of the included Air it did not appear by the depression of the opposite scale to be grown manifestly lighter than it was at first And the Bladder seem'd also to retain the same weight after it had by the Air that was let into the Receiver been compressed into its former wrinkled state NEW EXPERIMENTS About the Differing PRESSURE Of Heavy SOLIDS and FLUIDS NEW EXPERIMENTS About the differing Pressure of Heavy Solids and Fluids SInce not only in vulgar Spectators of Physico-Mechanical Experiments but even among some Learned men it has prov'd a great impediment to mens freely acquiescing in
between the effects of the Pressures made upon Bodies by incumbent or otherwise applied solid weights and those that they suffer from heavy but every way ambient fluids as will appear by the Experiments to be mention'd by and by From the particulars contained in these considerations we may be assisted to shew why 't is not necessary that the pressure of the Atmosphere though as great as we suppose it should oppress and crush the bodies of men that live under it for the solidity of the bones and the strong Texture of the membranes and fibres and the spring of the Aereal particles that abound in the softer as well as in the fluid parts of bodies is equivalent to the pressure of as much of the Atmosphere as can exercise its pressure against them and makes the frame of a humane body so firm that it may well resist the pressure of the outward Air without having any part violently dislocated whilst the external pressure is exercised but by the Air which being but an invironing fluid presses it equally as to sense on every side And because our bodies have been produced in the Atmosphere and from our very birth exposed without intermission to the pressure of it our continual accustomance to this pressure and the firmness of their structure keep us from being sensible of the weight or pressure And that it was not impertinent for me to mention the firmness of the frame of our bodies on this occasion I shall manifest by an instance that will upon another account also be proper for this place We know that multitudes of men have had occasion to pass over high mountains and besides that I have been my self upon the Alps and Apennines I have enquired of Travellers that have visited the Asian and American Mountains and some that have been upon the top of the Pick of Tenerif it self But though divers of them took notice of a great difference in the Air at the top and bottom as to some other Quality as coldness and thinness yet I never met with nor heard of any that took notice of a difference as to the Weight of Air he sustained or that complained that when he was come down to the foot of the Mountain he felt any greater compression from the Air than at the top And yet the Experiments made as well by others as by our selves sufficiently witness than on more elevated parts of the Earth which have a less height of the Atmosphere incumbent on them the weight and pressure of the Air is not so great as below And on very high Mountains 't is not unlikely that this difference may be very considerable since when the Torricellian Experiment was made near Clermont in France upon the Puy de Domme which is none of the highest mountains in the world being found by the ingenious makers of that observation to be but about 500 Fathoms they found the difference of the Mercury at the top and bottom to amount to about three inches And consequently if the tryal had been made with Water instead of Quicksilver the difference would have been about three foot and a half in the perpendicular height of the Water And 't is very probable that in much higher Mountains the difference of the Mercurial Cylinders height at the top and bottom may be much greater and at the bottom of some very deep Well or Mineral groove which may without improbability be supposed to be placed at or near the foot of one of these Mountains if we conceive the Baroscope to be let down the variation of the height of the Mercurial Cylinder may be yet much more considerable and yet we find not that the diggers in the deepest Mines in mountainous Countries are sensible of being lean'd on or compress'd by any unusual weight But not here to build on any thing but matter of fact it appears by the newly named observation that when a man was at the bottom of the hill he had as much greater weight of Air leaning upon his head than he had at the top as was equal to the height of an imaginary vessel full of water which having his head for basis were three foot and a half high which is so considerable a weight as could not but have been not only sensible but very troublesome and uneasie to support And what has been said of the gravity of a pail of water that leaned on his head may be proportionably appli'd to his Shoulders Arms c. Whence I think I may infer that the reason why such a weight was not felt by the man it compress'd was not that the Air that pressed him was not considerable but that the pressure was exercised after the uniform manner of fluid Bodies And this may suffice to shew that there is no necessity that the compression of the Atmosphere should make it impossible to live in it But because 't is observ'd that those that dive to great depths under water are not oppressed by the great weight of the incumbent water and the cause of this strange Phaenomenon is not so easie to be assigned and therefore has been made one of the two grand arguments whereon the non-gravitation of water in water and air in air has been and still remains founded I shall here offer something ex abundanti towards the solution of that noble and difficult Problem And first that what is observ'd by the Divers does not evince that water does not weigh in water I have elsewhere * See the Hydrostatical Paradoxes prov'd by such reasons and Experiments as had the good fortune to convince eminently learned men that were sufficiently prepossess'd with the vulgar opinion And in the same Treatise I have given a clear account why a Bucket full of water is not felt considerably heavy whilst 't is under water in comparison of what 't is whilst 't is drawn up into the Air which is the other Phaenomenon that I freshly intimated the common Opinion to be founded on Next I do not think it strange that that follows not which 't is objected should follow from our Hypothesis namely that a Diver should be violently depress'd to the bottom of the water by the weight of so great a Pillar of the Sea as is plac'd perpendicularly over his body For if we imagine a plane so to cut the sea-Sea-water as to pass by the Divers body then as that part of the plane on which his body leans will be press'd by It together with the water that is perpendicularly incumbent on it so all the other parts of the same plane will be pressed by equally tall Pillars of water perpendicularly incumbent on them and consequently if the mans body were just equiponderant to an equal bulk of water it and the water that leans on it would be sustain'd by the pressure of the collateral water incumbent on the other parts of the same plane as may be easily understood by what I have elsewhere said * See Appendices to
of Brass above-mentioned we put a fine Bladder tied so close at the neck that none of the Air whereof it was about half full could probably get out Which we did to the end that the Hen-Egge we were to bed in it might lie soft and have its sides almost cover'd with the limber and flaccid Bladder and contained Air This done we covered the remaining part of the Egg with another Bladder that nothing that was hard might come to bear immediately upon the shell then we put the wooden plugg into the Cylinder and a weight upon the plugg which is to be done very slowly and warily lest the quick descent of the weight should make the plugg break the Egg it leans on Lastly the Cylinder thus fitted being cover'd with a large Receiver and the Air being drawn out that air which was tied up in the Bladders by degrees expanded it self so strongly as to lift up the plugg and the incumbent weight to a pretty heigth and keep it there till the external Air was readmitted Now since 't will be readily granted and appears by divers Experiments elsewhere related that the Air in such cases expands it self vigorously every way it appears by the recited tryal that it pressed against the Egg with the same force that it press'd proportionably against the bottom of the Plugg and that force was more than sufficient to lift up the weight which together with the Plugg amounted to about thirty pound and yet the Egg being taken out appeared perfectly whole and no way harmed whereas upon the same Egg if I mistake not or at least another of the same kind laying warily a while after small weights one upon another the Egg was crush'd to pieces by about four pound weight This Experiment though it seem'd considerable to those that saw it and may prevent an objection for which reason I here mention it yet will appear in no way strange to them that consider that the weight of the Atmosphere which the Egg supported before it was put into the Cylinder was more than aequivalent to such a pressure of the Air as may suffice to lift up the plugg Wherefore I thought fit to make further tryals of a differing nature EXP. II. We took a Glass-buble of about an inch and half in Diameter which we caused to be blown at the flame of a Lamp that it might be far more thin and easie to break than the thinnest Vials that are wont to be blown in the Glasser's Furnaces This Buble we included between Bladders as we did the Egg in the former Experiment and then having warily put the plugg into the Cylinder so as it might press upon the Bladder that inviron'd the Glass we leisurely put the weights upon the Plugg till they together with the Plugg amounted to 30. pound or more which being removed the Plugg was taken out and the Glass-buble though it were extraordinarily thin perhaps no thinner than fine white Paper was taken out whole EXP. III. But lest the great resistance of so thin a Glass which yet was not Hermetically sealed should be ascribed to the Sphaericalness of its figure we imploy'd instead of it the shell of an Egg whence by a hole made at one end of it the Yolk and White had been taken out This empty and imperfectly closed shell we handled as we did the Glass-buble in the former Experiment and notwithstanding the great leaden weight that leaned by the intervention of the plugg upon the soft body that invironed it It was taken out not only uncrushed together but for ought we could perceive without the least crack EXP. IV. And to shew that what we observed about the nature of the compression of fluid bodies will hold as well in Water as Air though it seemed difficult to make the tryal with the accommodations we then had we thought upon the following Expedient Into a limber Bladder almost full of water we put a Hen-Egg and tying the neck very strait that nothing might get in or out we so plac'd the Bladder in the Brass-Cylinder that the Egg might not be immediately touched by any thing that was hard then putting the Plugg into the Cylinder we warily and leisurely heaped upon it flat-bottom'd weights of Lead conveniently shaped till they amounted if both I and another misremember not to about 75 pound notwithstanding all which the Egg was taken out sound and uncrack'd and probably might have supported a much greater pressure if we had been furnished with more weights of a commodious figure to heap upon it If we compare with this what was noted at the close of the first Experiment about the breaking of an Egg with four pound weight when no fluid body was interposed it will be obvious to conclude how great a difference there is between the resistance that a body may make to the pressure of solid bodies that bear hard against some parts and not against others and its resistance to others that compress it uniformly or in all places alike For though it be denied and that I think upon very insufficient grounds that bodies under water are pressed by the incumbent water because as 't is pretended the Elements gravitate not in their proper place yet this objection cannot be pretended to take place in our last Experiment where the main thing that leaned upon the water which surrounded the Egg being not a Pillar of Homogeneous water but a great and solid weight of Lead the included Egg must by the intervention of the water have been compressed Nor were Eggs the only bodies we endeavour'd to crush after this manner the tryal having been also made upon a substance more soft and of a very irregular shape To apply this now to Divers when they are at a moderate depth under water it seems not improbable that the structure of their bodies should be robust enough not to be violated by the pressure of the incumbent and otherwise ambient water For we have seen by the former Experiments and especially by the last recited that a body easie to be broken inwards by an incumbent solid weight will remain intire and unaltered in point of figure under a very much greater weight that compresses it after the manner of an ambient fluid And though it would seem to many that even in our supposition the Thorax being as they think it a kind of empty space in the body the ribs and muscles ought by the weight of the water to be crushed into the great cavity intercepted between them yet it is to be considered on the other side that the Air contained in the chest especially when its Spring is increased by those accidental causes that may take place when men are deep under water particularly the praeternatural heat which the want of the usual respiration is apt to produce will very much help the chest to resist the pressure as they will easily grant that have tryed the resistance that Air makes to be considerably compressed under water the difficulty of farther compressing it still encreasing as in Springs it ought to do the more it is compressed And I further observe that the structure of the Thorax is much more firm than men are wont to suppose as appears by the very great solid weights that some men do for gain or to shew their strength suffer to be laid on their breasts without receiving any mischief thereby And if I should admit that at great depths the water had some little compressive operation upon the chest yet that can be no other than the pressing the parts a little inwards and that the structure of the Thorax it self fitted by nature for constriction and dilatation as may appear in vehement takings in and blowings out of the Air may admit with small inconvenience To which purpose I recall to mind what I lately mentioned concerning the Physician that found his Thorax somewhat compressed when he leisurely dived as also what I have * In the Append. to Hydrost Paradox elsewhere delivered concerning a Tad-pole which swimming in water that was strongly compress'd by an external force seemed thorough the Glass that contained the water to be somewhat lessen'd in bulk and yet not killed nor sensibly crushed notwithstanding its great tenderness And if there were parts of a human body that were of a Texture too weak and too disproportionate to the rest I think it possible that this compression inwards might be great enough to be very sensible to the Divers For having purposely inquired of a certain man whose trade 't was to fetch up goods out of Ships cast away by the help of a diving instrument he told me that when he was at a considerable depth under water as about ten or twelve Fathoms he found suitably to my conjecture so great a pressure against the drums or thin membranes of his Ears which were not sufficiently counterpress'd from within as put him to a great deal of pain till he had found some contrivances to lessen the inconvenience Nor was this man the only Diver that has complained of this troublesome pressure which seems to argue that at least at great depths under water the firmness of the structure of a mans body does concurr with the uniformity of the fluids pressure to keep him from being hurt by the incumbent and otherwise ambient water But I shall now say no more of the Problem obout Divers since besides that the matter of fact is not yet in my opinion accurately enough stated and determined the true solution of it is not necessary to give a reason why the weight of the Air a fluid so much lighâ—er than water should not oppress nor crush the bodies of Animals though what has been already said about the resistance of bodies under water may serve very much to confirm the reasons I propos'd why we that live in the Atmosphere are not sensibly compress'd much less oppress'd by its weight FINIS ADVERTISEMENT THe Reader is desired to take notice that of this Tract concerning the Differing Pressure of heavy Solids and Fluids there have been lost by the carelesness of the Printer Eleven written pages which he under his hand had acknowledged to have received and with the contents of which many of them being Quantities and other circumstances of Experiments formerly made the Author cannot now charge his memory
besides create another difficulty to which we found middle-sized Receivers also obnoxious For several times when the Experiment required an intense heat within the Receiver then especially if some casual obstacle hinder'd the quick exhaustion the heat of the ignited Iron or some such other included body would so melt or soften the Cement that fasten'd the Receiver to the Engine that when the Glass was brought to be well exhausted and sometimes also before the external air would by its pressure and fluidity squeeze or thrust in somewhere or other the yielding Cement and thereby cause in the Instrument a leak that would much incommodate us if not reduce us to begin the Experiment again in so much that for some tryals we were fain to provide a Cement on purpose the least fusible that we used on other occasions being yet found too fusible on these Nor were those I have already mentioned the only difficulties and impediments I met with in making experiments about Flame and Air but I shall not here trouble you with them in this place where it may suffice for me to have mentioned those that are of a more general nature and are like the most frequently to occurr But though I declin'd to name any other to you than the foregoing difficulties in making the following Experiments yet I must not omit to take notice of one that may occurr to you about judging of them For in those tryals that require to have an ignited Iron or any such thing included in the Receiver it would usually happen that so much heat would rarifie the Air shut up in the Mercurial Gage and consequently inable it to depress the Mercury that lies under it far beneath the mark it would have staid at upon the meer account of so much ambient Air pump'd out This would happen I say before the heated Receiver was well exhausted so that if one be not aware of this 't will be obvious by looking on the Gage to conclude the Receiver to be well emptied before it really is so And therefore the safest way in these cases is to continue to pump without trusting to the ordinary marks till you see that the Mercury will be no further depressed in the sealed leg of the Gage though otherwise by concurring signs one that is vers'd in those tryals may well enough judge when he needs to pump no longer But perhaps you will here demand whether by our Engine we can competently withdraw the Air out of a Receiver or whether at least that may not be much better done by the help of Quick-silver after the manner of the Torricellian Experiment in regard that ponderous liquor frees the glass it deserts from all the Air at once and exactly hinders the regress of it In answer whereunto I hope you do not expect that I should contend for a favourabler judgement of the Engine I employ than the Virtuosi as well Foreign as English have been pleased to pass on it already And therefore to tell you freely my thoughts about the main part of the propos'd Question I shall readily avow to you that I think there may be experiments such as some of those where the included body need be but small and where the being suddenly produc'd is chiefly desired in the effect wherein by the help of Quicksilver the exhaustion of the Air may be dispatch'd with greater celerity and consequently make the effect be more conspicuous than by our ordinary way of trying it would be in our Engine since the fall of the Mercury does as the objection intimates produce a Vacuum in our sence of that word very nimbly whereby the Expansion of the Air is presently effected and the Aereal particles harboured in the pores of any body plac'd in this deserted cavity will thereby have opportunity more suddenly to expand themselves But on the other side I might answer in general that when I have particular occasions to dispatch the exhaustion of the Air I can very much hasten it by barely lessening as I have several times done the capacity of the Receiver insomuch that I have sometimes imployed so small an one that in half a minute or much less after it was fitted on we could considerably exhaust it and thereby produce Phaenomena exceeding conspicuous And as to the Experiments of this little Tract in particular it may be said that not to mention the troublesomness and other inconveniencies of needing to imploy such an unwieldy weight of Mercury you will easily find by the Phaenomena of divers of the insuing tryals that most of them cannot be with any conveniency and some of them not at all made in the Torricellian tubes As for the ground of the Objection that the Air cannot be so well drawn out by our way as by the subsiding of the Mercury though you may think that very clear yet one that were very jealous of the Reputation of the instrument I employ may perhaps reasonably enough question it For the Vacuum that is produced in the Torricellian Experiment as 't is made all at once so 't is made once for all and therefore if there were any Aereal particles lurking in the Mercury as there will be pretty store if the quantity of that liquor be great enough to make a considerable Vacuum which if it be not it will be too small for very many of our tryals they will remain in the deserted cavity at the top of the Glass and by their expansion there much hinder the full operation of an ambient Vacuum upon the bodies plac'd in it Befides that almost all such bodies if they be dry will be so incongruous to Mercury which scarce sticks to any consistent bodies but metals that probably there will be no small number of aereal corpuscles intercepted between the Mercury and those surfaces to which it does not closely adhere which aery corpuscles when the subsiding Mercury deserts them will be left to increase the number of those that as we were saying will emerge from the Mercury from which as also from the pores of the included bodies will perhaps arise divers new ones from time to time for a pretty while after And in case the Vacuum be made by a Cylinder of two or three and thirty foot of water as for some experiments that have been tried in France and Italy hath been done the emersion of bubles may last a long time as may be gather'd from some observations of mine elsewhere related On the contrary in our Engine though when the Receivers are not very small they are more slowly emptied yet in recompence we may continue the pumping out of the Air as long and renew it in the same Experiment as often as we think fit So that if we perceive that after the first exhaustion of the Glass there happen any aereal particles to extricate themselves successively out of the included body we can by resuming the Pump from time to time whenever need requires free the Vacuum from these also which in
purpose and furnish'd with a very slender wieke which the mixture would not burn whilst there was liquor enough to imbibe it well and putting this lighted Lamp into a convenient place of a Receiver that was not small since it was able to contain about two gallons or sixteen pound of water we made hast to cement on the glass to the Engine and yet found not in two or three several tryals that after the Pump began to be moved so little a quantity of tincted flame in that capacious Glass lasted much if at all more than half a minute of an hour estimated by a minute watch And because the Receiver we then made use of seem'd to me by reason of its size and some accommodations that belong to it proper enough to be imploy'd about other tryals concerning the relation between Flame and Air I thought fit to try with the same small Lamp and liquor what other Phaenomena of that kind would be afforded by letting Air in and out according to the various exigencies of my particular aimes But not having then nor in some time after the leisure and opportunity of setting down things circumstantially I contented my self to take those short Notes of the Principal things whereof I now subjoyn the transcript When the flame began to decay the turning key being now and then drawn almost out the tincted flame lasted once a minute and a half and another time longer The turning key being taken out in the beginning the flame lasted two minutes or better A Pipe bedded in the cement at the bottom of the Glass and having at each end an open orifice almost of the bigness of that filled by the turning key which key was then removed from the top the tincted spirit seem'd to burn very conveniently as if the flame would have burn'd very long if we would have permitted it so to do The orifice at the top being stop'd with the turning key though the Pipe were left open at the bottom it plainly in a short time seem'd much to decay and ready to expire whereupon I caus'd one to blow constantly yet but very gently in at the pipe with a pair of bellows and by this means though we did not keep the flame vigorous yet we kept it alive for above four minutes and then observing it to be manifestly stronger than it was when we began to refresh it with the Bellows we ceas'd from blowing and found that though the Glass-pipe was still left open yet within about one minute the flame was quite extinguished EXPER. V. Of the Conservation of Flame under water THe better to examine the necessity of Air to Flame I thought fit not only to make the several Tryals mention'd in this Paper whether it would live in a medium much thinner than Air but also to try whether it would be able to continue in a medium many hundred times thicker than Air namely in Water I doubted not but many would think this both an easie and a needless Inquiry since eminent Writers both Ancient and Modern tell us without scruple that Naptha and Camphire will burn under Water but I had never the good fortune to be able to make them do so and may be allowed to doubt whether these Writers notwithstanding their confidence deliver what they affirm upon Experience not bare Tradition And though in celebrated Authors I have met with divers Receipts of making Compositions that will not only burn under water but be kindled by it yet I have found those I had occasion to consider to be so lamely or so darkly and some of them I fear so falsly set down that by the following composition how slight soever it may seem I have been able to do more than with things they speak very promisingly of since though 't will not be kindled by water yet being once kindled it will continue to burn under water And that there might be no suspicion that whilst the mixture continued under water it did only as it were vehemently ferment or suffer a violent agitation of its parts without having them kindled till in their ascending they were actually fired by the contact of the air incumbent on the surface of the water To obviate this suspicion I say we were careful to try the Experiment not only in other Vessels but in a large Glass the transparency of whose sides as well as that of the contained water would permit us to see for a while the burning of our composition which was sometimes with a weight detain'd and sometimes with a Forceps held till 't was consumed a good way under the surface of the Water The way of making the Experiment is this We took of Gunpowder three ounces of well burnt Charcoal one drachm of good Sulphur or flower of Brimstone a little less than half a drachm of choice Salt-petre near a drachm and half Which Ingredients being well reduc'd to powder and diligently mingled without any liquor either a large Goose-quil whose feathery part was cut off or a piece of a Tobacco-pipe of two or three inches long and well stop'd at one end had its cavity well fill'd with this mixture instead of which beaten Gunpowder alone might serve if it did not operate too violently or waste too soon For the kindling whereof the open orifice of the Quil or Pipe was carefully stopt with a convenient quantity of the same mixture made up with as little Chymical Oyle or Water as would bring it to a fit consistence This Wild-fire was kindled in the Air and the Quill or Pipe together with a weight to which 't was tied to keep it from ascending was slowly let down to a convenient depth under water where it would continue to burn as appeared by the great smoak it emitted and other signs as it did in the air because the shape of the Quil or Pipe kept the dry mixture from being accessible to the water that would have disorder'd and spoil'd it at any other part than the upper Orifice and there the stream of kindled matter issued out with such violence as did incessantly beat off the neighbouring water and kept it from entering into the cavity that contain'd the mixture which therefore would continue burning till 't was consumed 'T is probable that most men will conclude from this Experiment that Air is not so absolutely necessary to the duration of Flame as some other of our Tryals seem to argue and that there ought to be a difference made between ordinary Flames and those that burn with an extraordinary vehemency But my design being as I long since intimated rather to relate Tryals than debate Hypotheses I shall only add that it may be pretended on the behalf of the opinion that this experiment seems to disprove that not to mention the Air that may lurk in the Pores of the Water or that which may be intercepted between the little grains of Powder whereof the mixture consists the Salt-petre it self may be suppos'd to be of such a
it would well stretch filling also the stem and cavity of the Glass with very red sumes which presently after forced their way into the open Air in which they continued for a good while to ascend in the form of an Orange-colour'd smoak EXPER. II. Of an Explosion made with Oyl of Vitriol and Oyl of Turpentine IF I had at hand the Papers you have divers times heard me speak of about Heat I could give you the particulars of some Tryals about Explosion that perhaps you would think more pertinent than despicable but for want of those Papers I must content my self to tell you in general That I remember that I have more than once taken strong Oyl of Vitriol and common Oyl of Turpentine and warily mix'd them in a certain proportion by shaking them very well together and that thereupon insued what I had reason to look for so furious an agitation of the minute parts of the mixture and so vehement or sudden Expansion or Explosion as did not only seem strange to the Spectators but would have prov'd dangerous too if I had not taken care before-hand that the Tryals should be made in a place where there was room enough and that even the Operator that shook the vessel should stand at a convenient distance from the mixture EXPER. III. About an Explosion made by two Bodies actually Cold. I Remember not that I found the Assertors of Explosions in Animals to have taken notice of a difficulty which to me seems not uneasie to be observ'd and yet very worthy to be cleared For 't is known that Fishes and those especially of the vaster sort can move and act in the waters with a stupendious force and yet it is affirm'd by those that pretend to know it that the Blood of most Fishes is still actually cold And I remember I found the blood even of those I dissected alive to be so From whence most men would argue that even in the vast Sea-monsters there can be made no Explosions these being still effected by or accompanied with an intense degree of heat 'T were incongruous to my design to examine this difficulty as it directly regards the Explosions said to be made in Animals But speaking of Explosions in general perhaps I might do the favourers of vital ones if I may so term them no unacceptable piece of service by experimentally shewing that 't is not impossible though it seem very unlikely that Explosions should be made upon the mixture of bodies which whilst they seem to put one another into a state of Effervescence are really cold nay colder than before their being mingled Of these odd kind of mixtures I remember I have in another * About the Preduction or Extrication of Air. paper set down some Tryals that I made to other purposes as well with two liquors as with a liquor and a solid body which later sort I there mention my having made by an improvement of an experiment of the excellent Florentine Virtuosi And among those Tryals I find one whose pertinency to the matter in hand invites me to annex as much of it as is proper in this place There were put two ounces of powder'd Sal Armoniac into a pretty large Glass-tube Hermetically seal'd at one end into the same a slender Glass-pipe furnished with two ounces of Oyl of Vitriol was so put that when we pleas'd we could make the liquor run out into the larger Tube which after these things were done was clos'd exactly so that nothing might get in or out My design was that this instrument should be so warily inverted that the Operator might get out of the way and the Oyl of Vitriol falling slowly upon the Sal Armoniac should without producing any heat produce an explosion not dangerous to the By-standers But whilst I was withdrawn to a neighbouring place to write a Letter the Operator not staying for particular directions rashly inverted the instrument without taking care to get away whence it happen'd that as soon as ever the contained liquor being too plentifully poured out came to work on the Sal Armoniac wherewith it is wont to produce cold there was so surprizing and vehement an Expansion or Explosion made that with a great noise which as the Laborant affirmed much exceeded the report of a Pistol the Glasses were broken into a multitude of pieces many of which I saw presently after and a pretty deal of the mixture was thrown up with violence against the Operators Doublet and his Hat which it struck off and his face especially about his eyes where immediately were produc'd extreamly painful tumors which might also have been very dangerous had I not come timely in and to add that upon the by made him forthwith dissolve some Saccharum Saturni in fair water and with a soft spunge keep it constantly moisten'd by very frequently renewed applications of the Liquor By Gods blessing upon which means within an hour or two the pain that had been so raging was taken away and the fretting Oyl of Vitriol was kept from so much as breaking the skin of the Tumors that it had made The first part of the Relation of this tryal might have been omitted or at least shorten'd unless I had design'd to communicate unto you a way of doing what I do not know to have been attempted by others namely to put bodies together when and by what degrees one pleases after the Glass that contains them has been Hermetically seal'd up which Mechanical contrivance especially as it may be varied may be as I have try'd usefully apply'd to more purposes than 't were proper here to take notice of But to conclude with a word or two touching the foregoing Experiment I shall only add That another time we made a like tryal a safer way by tying a Bladder so to the top of a Bolt-head into which we had before-hand put the Sal Armoniac that by warily moving the Bladder whence the Air had been express'd we could make some of the Sal Armoniac we had lodg'd in its folds to fall upon the liquor with which it presently made an Explosive mixture that quickly blew up the Bladder But these Sir are bare Conjectures left to be after a farther discussion if you think them worthy of it determin'd by You to whom as these Papers are address'd so they are also submitted by the Writer of them Who is Sir Your most c. AN HYDROSTATICAL Discourse Occasioned by The Objections of the Learned Dr. Henry More AGAINST Some Explications of New Experiments made by Mr. Boyle AND Now publish'd by way of PREFACE to the Three ensuing Tracts ADVERTISEMENT THis Hydrostatical Discourse distinguished by small letters for the Signature is to be placed immediately before the Title New Experiments of the Positive and Relative Levity of Bodies under Water TO The Reader WHen I determin'd to write this Polemical Discourse I did not forget that when I first ventur'd some of my trisles abroad into the world my friends obtain'd
ambient air from Glass-Bubbles hermetically sealed with air in them not compress'd beyond its usual state the Spring of the Internal air would make the Bubbles fly in pieces And this will happen to stronger Glasses than Bubbles as you will find in one of the former Experiments * See the Tract about the Pressure of the Airs Spring on bodies under water And if we would illustrate what we are debating of by an Example it should not be by considering as the Doctor does the endeavour of five men against the sixth that hath his back to the Wall but that of five Bladders full of air pil'd up and resting upon a sixth For in this case whatever force or power of pressing we suppose in the incumbent Bladders they all bear jointly upon the lower which continuing at a stand must thereby be so compress'd as to be able to resist their joint endeavours as 't is manifest because otherwise it would not continue in that state but be farther compress'd which is against the supposition This Notion about Pressure and Resistance I have the more particularly deduced because I found many modern Naturalists and even Hydrostaticians themselves to be great strangers to it For which reason I shall add that I have evinc'd it by purposely devised Experiments in the Continuation of the Physico-Mechanical Experiments * Exper. 25. and elsewhere about the Air. Were it not for this I should perhaps have spared my self the labour of setting down these thoughts as not necessary to the solution of the Doctors Objections For he admits a Layer or as he aptly speaks an Area of Aerial Particles to be interposed between the upper Marble and the Wooden Plate and therefore the flatness and stiffness of those two Bodies must keep them from an immediate contact as well at the edges as by the help of the same Area they do elsewhere and consequently that interposed Air may communicate with the ambient Air. From whence the Laws of the Hydrostaticks which I have elsewhere shewn will allow me to conclude that the weight of the Atmosphere endeavours to depress the upper surface of the wooden Plate and so what the Examiner urges of the inconsiderable resistance that the few Aerial Particles interposed between the flat Bodies can make to the great pressure of the Column of Air that thrusts the Woodden against the Marble Plate would not conclude though our former answer could not have been made since the resistance made by the interposed Aerial Particles to the pressure upwards of the Atmosphere is not in our present supposition made by those Particles alone but by the weight of the lateral and superior part of the Atmosphere exercised by the intervention of these Particles Which being so what the Learned Doctor adds that the weight of the wooden Plate it self is here of no consideration must needs be a mistake For the two equal Atmospherical Pressures the one against the upper surface of the woodden Plate and the other against the lower countervailing and consequently frustrating the endeavour of each other the gravity of the wood it self will suffice to make it fall as well as if it were press'd against by neither of them And from this Discourse you will easily judge whether the Doctor had reason to say as he does * p. 146. Quam ab omni ratione igitur absonum est ut superficies illa sive area aerearum particularum quae insinuant se laminam ligneam inter marmor solidam columnam hujusmodi particularum vi elastica sursum enitentium contra laminam ligneam obnitendo vincat ipsamque laminam in terram deturbet CHAP. VI. WHat he adds in the sixteenth number against those that fancy the Aerial Particles to be endow'd with Perception and to act with Design pro re nata does not at all concern me and what he adds in the next Paragraph wherewith he concludes his twelfth Chapter I shall altogether pass by as far as it concerns the extravagant conceit he opposes But because at the close of the Paragraph he makes an Inference which comprises our Opinion also since he concludes that the Experiment by him alledged * p. 150. Certissimum est indicium particulas Aerias nec cum consilio nec sine consilio inferius marmor sustinere nec suffulcire It will not be amiss to shew that our Opinion is undeservedly included in the Inference which I shall do by briefly solving the Phaenomenon the Doctor layes so much weight on For if we conceive with him that the two flat Marbles formerly mention'd be suspended and that to the lower of them a flat woodden plate of the same shape and extent be applied I see no cause to wonder why the two Marbles should stick together and not the lower of them to the woodden plate For as I lately noted there being an Area or Bed of Aerial Particles interpos'd betwixt the Marble and the Wood the weight of the Atmosphere exercised by the intervention of those Aerial Corpuscles ought to be aequipollent to the pressure of the Atmospherical Cylinder that bears against the lower surface of the Plate which consequently by its own weight must drop down whereas there being no such Layer of Aerial Particles interposed betwixt the two Marbles the pressure of the ambient Atmosphere which touches them every where save where their polish'd surfaces are contiguous must keep them strongly coherent I presume I need not mind you that hitherto I have discours'd upon supposition that the Doctor experimentally knows what he delivers concerning the Non-adhesion of an exactly smooth woodden Plate to a Marble one And upon his concession that because of the want of sufficient congruity between the surfaces of two Bodies there is a bed of Aerial Corpuscles interposed between them But now I think it will not be unfit to take notice to you that though to illustrate on this occasion a subject that is generally so little understood as the exercise of Pression among fluid Bodies I have answer'd my Learned Adversaries Objections as if I had nothing more to say for my Explication of the Suspension of coherent Marbles than what I many years since deliver'd in the little Tract by him cited yet I have since abundantly confirmed that Explication by the 50th of the Experiments publish'd in my Continuation which if the Doctor had been pleased to read perhaps he would have received the same satisfaction that other Learned men have done since there I experimentally shew that the undermost Marble without the accustomed Clog would upon the bare withdrawing of the sustaining air drop off from the upper And whereas the two Marbles in our Vacuum would not cohere as soon as the formerly excluded Air was let in upon them it did by its supervening pressure make them stick together very strongly THE SECOND SECTION CHAP. I. I Proceed now to the second of those two Chapters that I am interess'd to consider in which the Learned Examiner is pleased
to attaque three or four of my Hydrostatical Opinions and Explications in the defence whereof I hope I shall be the less put to exercise your Patience because the Learned Doctor himself is pleased to grant me almost as much as I need desire concerning the Truth of the Hypothesis whereon my Paradoxes and Explications are founded For whereas the main thing I suppos'd in my Hydrostatical Papers is that in water though stagnant the superior parts do actually though not always prevalently gravitate upon the inferior or if you will press upon them even when they do not sensibly depress them the Doctor in divers places allows this Hypothesis to be consonant to the Principles of the Mechanical Philosophy and accordingly having shew'd that in a suspended tub of water the whole liquor gravitates upon the bottom of the tub He subjoyns * P. 161. Jam verò cum tota haec aqua constet ex particulis aqueis non compactis vel concretis sed solutis à se invicem impossibile est ut omnes fundum situlae premant nisi infima quaeque ab omnibus superioribus prematur quemadmodum clarè demonstravimus in secunda sectione hujus capitis nempe si nullae causae nisi purè Mechanicae quales sunt Motus localis Magnitudo Figura c. in edendo hoc Phaenomeno se intermiscent And elsewhere in the same Chapter he speaks thus of the gravitation of liquors towards the close of the second Paragraph * p. 152. Necesse utique est ut partes singulae gravitent cum totius sit gravitatio si non sit aliquid immateriale Principium in rerum natura c. And adds at the beginning of the next Number Atque sanè huic externi motûs Hypothesi gravitationis Elementorum in propriis locis inde necessariò emergentis apprimè consonum est primum illud Experimentum quod Scriptor profert in Paradoxis suis Hydrostaticis And now Sir I presume you do not much wonder if I think these concessions reach the main thing I pretend to For though I do as freely and heartily as the Doctor himself who I dare say does it very sincerely admit or rather assert an Incorporeal Being that made and governs the world yet all that I have endeavour'd to do in the Explication of what happens among Inanimate Bodies is to shew that supposing the World to have been at first made and to be continually preserv'd by Gods divine Power and Wisdome and supposing his General concourse to the maintenance of the Laws he has established in it the Phaenomena I strive to explicate may be solv'd Mechanically that is by the Mechanical affections of Matter without recourse to Natures abhorrence of a Vacuum to Substantial Forms or to other Incorporeal Creatures And therefore if I have shewn that the Phaenomena I have endeavour'd to account for are explicable by the motion bigness gravity shape and other Mechanical affections of the small parts of liquors I have done what I pretended which was not to prove that no Angel or other immaterial Creature could interpose in these cases For concerning such Agents all that I need say is that in the cases propos'd we have no need to recurr to them And this being agreeable to the generally own'd rule about Hypotheses that Entia non sunt multiplicanda absque Necessitate has been by almost all the modern Philosophers of different Sects thought a sufficient reason to reject the agency of Intelligences after Aristotle and so many Learned men both Mathematicians and others had for many ages believ'd them the Movers of the Celestial Orbs. CHAP. II. But you will tell me that the Doctors Concessions will not avail me since he urges against the Gravitation of the Elements in their proper places which gravitation he would have to be suspended by his Incorporeal Principle an Experiment which he says is most manifestly repugnant to our Hypothesis He conceives then that in a tub or pail full of water with a perfectly Cylindrical cavity whose Diameter is of sixty two parts there is violently kept at the bottom by the help of a stick a round Plate of wood whose Diameter amounts but to sixty one of those parts and that as soon as ever the stick is removed the woodden plate will emerge to the top and float Quod says he prorsus impossibile esset si omnes partes aquae ab FG ad HJ non solùm junctim fundum vasis sed singulae singulas in eadem serie subjectas actu premetent To which assertion he immediately subjoyns this Argument to prove it by * p. 155. Cum Diameter laminae ligneae H M partes 61. habeat aequales Diameter vasis HI habeat 62 manifestum est quod superficies fundi vasis ad superficiem laminae se habet ut 3844. ad 3721 quorum differentia est 123. Itaque rotundum intervallum inter latera vasis marginem laminae ligneae habet se ad aream laminae ut 123. ad 3721 hoc est area laminae ligneae excedit aream dicti intervalli plusquam triginta vicibus Ac proinde aqua incumbens ligneae laminae excedit magnitudine aquam incumbentem dicto intervallo inter marginem laminae later a vasis plus quà m triginta vicibus pondúsque sive pressio hujus alterius pondus pressionémque vincit plusquam triginta vicibus Adeò ut impossibile sit ut aqua incumbens praedicto intervallo ita premat aquam ipsi subjectam ut hujus vi sublevetur lamina quam vis tricies major deprimit Quod says he by way of inference aeque absonum atque absurdum Phaenomenon esset c. How little this Ratiocination agrees with the Experiments I have formerly told you of about the cases wherein Light bodies will be detain'd under water or emerge to the top of it you will easily perceive if you compare the one with the other which you may quickly do if you please to compare the Doctors discourse with the following Narratives of those Tryals * See the Tract of the Positive or Relative Levity of Bodies under water Exp. 1. c. to which alone I might therefore refer you But yet in the mean time you may if you think fit consider a little whether the Argument whereon the Doctor lays so much stress be any more than a Paralogism First then since according to his computation the Area of the interval between the sides of the Vessel and the edges of the round boards is 123 of such parts whereof the Area of the board amounts to 3721 't is evident that there must be room enough for the water to pass between the sides of the vessel and the edges of the board which is suppos'd on all hands to be of some wood lighter in specie than water since else it would not emerge upon the withdrawing of the stick Next this Board or woodden Plate is not here intimated or supposed to be and indeed in practice can scarce
matter of fact is true But after I had in vain sought the Doctors meaning where I expected it chancing lately to cast my Eyes on another place where I saw my Scheme repeated I find this passage in the Explication he endeavours to give of the Phaenomenon by his Hylarchical Principle Cùm verò tam profundè immergitur tubus ut obturaculum tangat Superficiem V. W vis retractionis Aeris ita augetur ut etiam ponderis appensi superadditam depressioneâ— superet Videtur igitur quasi quaedâ—m sursum-suctio Aeris in tubo contenti conformis ac contemporanea aquae compulsio in obturaculum quo tam firmiter in os valvulae comprimitur ibique cum appenso pondere sustentatur What considerable interest the supposed but unprov'd Retraction of the Valve or the Air it self can have in this Phaenomenon I confess I do not discern not being able to see but that the experiment would succeed when tri'd in vacuo although all the Atmosphetical Air were annihilated But if I mistake the Doctors meaning I am to be excused since I do it not willingly and his own obscurity has been accessary to it Nor am I very apprehensive of being unable to defend my account of an experiment which as you know has had the good fortune to recommend the Doctrine for the Proof whereof I devis'd it to many Learned and curious Persons several of which were sufficiently indispos'd to admitt it And to avoid all mistakes and disputes that may arise which I think they must do needlessly upon the score of the Valve imploy'd in our Experiment I shall remind you of another that I remember I have some times shew'n you and divers other Virtuosi though I remember not whether I have mention'd it in any of my publish'd writings The Summ of this tryal is that an arbitrary Quantity of Quicksilver being by Suction rais'd into a very slender glass-pipe whose upper Orifice is stop'd with the Experimenters finger to keep the Mercury from falling before its time the open end of the pipe with the Mercury in it is thrust into a competently deep glass of water till the little Cylinder of Mercury have beneath the surface of the water attain'd to a depth that is at least 14 times as great as the Mercurial Cylinder has of height For then the finger being remov'd from the upper orifice the glass-pipe will be open at both ends and there will be nothing to hinder the Quicksilver's falling down to the bottom but the resistance of the Cylinder of water that is under it which Cylinder can resist but by vertue of the weight or pressure of the stagnant water that is superior to it though but collaterally plac'd above it And yet this water being by the pipe whose upper part is higher than its surface and accessible only to the air kept from pressing against the Mercury any where but at the bottom of the Pipe and being about a 14th part of the weight of an equal bulk of Mercury it is able at that depth to make the subjacent water press upward against the Mercury which is but a 14th part as high as the water is deep with a force equivalent to that of the gravity wherewith the Mercury tends downwards And to manifest that this Phaenomenon depends meerly upon the Aequilibrium of the two liquors if you gently raise the lower end of the pipe towards the surface of the water this liquor being not then able to exercise such a pressure as it could at a further and greater depth the Mercury preponderating will in part more or less as the pipe is more or less rais'd fall out to the bottom of the glass But if when the Quicksilver is at the first depth instead of raising the pipe you thrust it down farther under the water the pressure of that liquor against the Mercury increasing with its depth will not only sustain the Mercury but impell it up in the pipe to a considerable distance from the lower orifice of it and keep it near about the same distance from the surface of the laterally superior water And this experiment may not only serve for the purpose for which I here alledge it but also if duely consider'd and applyed may very much both illustrate confirm the Explication formerly given of the seemingly spontaneous ascent of the clogg'd sucker in our exhausted Air-pump The last Argument the Doctor urges against the Gravitation of water in what they call its proper place is deduc'd from what happens to the Divers who in the mid'st of the Sea though the salt water of that be much heavier than that of freshwater Rivers do not find themselves oppress'd or so much as feel themselves harm'd or compress'd by the vast load of the incumbent water But that the Equality of the pressures of an ambient fluid will goe a great way towards the solving of this Difficulty you will find by the Experiments and considerations you will meet with in the following * The Author means the New experiments of the differing pressure of heavy solids fluids Papers to which for that reason I referr you And though the Doctor in this same Paragraph objects Tametsi haec pressio aequalis sit nihil tamen impedit quò minùs subtiliores partes corporis magisque fluidas exprimat elidat I remember I answer'd that exception before by saying that those liquors that he supposes should be squeez'd out cannot be so because there is as great a pressure against those parts at which they should issue as against any of the rest if the parts that should be squeez'd out be not too spirituous and subtile which if they be I should gladly learn how the Doctor knows that no such minute and spirituous particles are really expell'd especially if that be observ'd which we shall soon have occasion to relate that a small animal being vehemently compress'd in water seem'd a little though but a little to shrink But that we may the more distinctly consider this grand argument taken from the experience of the Divers that is wont to be employ'd by the Schooles and others for the vulgar Opinion and is now urg'd by the Learned Doctor to prove His 't will be convenient to observe that it does at once both propose a Question and contain an Objection grounded upon the surmis'd insolubleness of that Question And to begin with the Probleme Whence it is that Divers are so far from being kill'd or oppress'd by the weight of the incumbent water that they are not so much as hurt by it nay that they scarce feel it at all We may take notice that there is in it somewhat suppos'd as well as somewhat demanded For in the Question 't is taken for granted that Divers though at never so great a depth feel no pressure exercised against them by the water which is an affirmation in point of fact of whose truth I make some question for the reasons I shall ere long have
nature cole-black alter and become afterwards a branded russet like to the hairs of Sea-wolves c. And a General of the English in the East-Indies being by them employed on an Embassy to the Emperour of Japan has this passage concerning some female Divers that he met with in his voyage * Purch Tom. I. Lib. 4. C. 1. All along this coast so up to Ozaca we found women Divers that liv'd with their houshold and family in boats upon the water as in Holland they do the like These women would catch fish by Diving which by net line they miss'd and that in eight fathom depth Their eyes by continually diving grew as red as blood whereby you may know a diving Woman from all other Women I know it may be said that these diseases may proceed from the coldness and moisture or other qualities of the Sea nor would I confidently reject such a surmise But it may also be possible that the compression they suffer'd under water might have at least a share in the production of these ill effects For how are we yet certain that the pressure of the water against their bodies though it does not manifestly dislocate any solid or firm part but only somewhat press inwards as in the above mentioned Tadpole the outward skin and the fibres both which will easily yield a little way without being painfully stretch'd may not by straitning the Vessels and otherwise inconveniently alter the circulation of the blood and the motion of the humors spirits and other fluid parts of the body And I am not sure that much of the cold that Divers are wont to complain of when under water may not be a disaffection produc'd in the nervous and membranous parts occasioned by the compression of the ambient water there being divers things and pressure among others besides actual cold that will make men complain of being cold and in our case this sensation may be excited or assisted by the hindering of the usual perspiration at the constipated pores of the skin And it seems not impossible that one not so ignorant and heedless as Divers are wont to be may refer a new sensation that really proceeds from pressure to other Causes since Learned and Intelligent men when prepossest as these Common Divers usually are with the vulgar opinion about the Non-gravitation of Water and Air in their natural places do almost always refer * The reason of which experiment may be gathered from the 4th Chapter of the Author 's long since publish'd Defence against Linus an experiment of my Engine to Suction which is indeed the effect of the pressure of the Ambient as I have †In a Paradox about Suction elsewhere clearly shewn and affirm that the pulp of the finger or hand is drawn up into a hollow Pipe into which it is indeed thrust by the weight of the Ambient air But all these things I have mentioned not as if I laid any great weight upon each of them but to let you see that 't was not altogether without cause that I complain'd of the incompetency of the History of what Divers feel under water especially at great depths where this want of information may be more considerable For as far as I have yet learnt by perusing Voyages and enquiring of Travellers of my acquaintance the places where they are wont to dive for Pearl are but moderately deep and indeed shallow in comparison of the great depths of the Sea so that if we were furnished with as many Relations of these profound places as we have of the others possibly the accounts would be different enough to render doubtful or to correct the received opinions about the conditions of Divers at the bottom of the Sea For I remember that a credible eye-witness who if I mistake not was the Intelligent Oviedo speaking of the Pearl-fishing on the American Island of Cubagna has among many other notable observations such a passage as this But whereas the place is very deep a man cannot naturally rest at the bottom by reason of the abundance of aery substance which is in him as I have oftentimes proved For although he may by violence and force descend to the bottom yet are his feet lifted up again so that he can continue no time there And therefore where the Sea is very deep these Indian Fishers use to tye two great stones about them with a coard on each side one by the weight whereof they descend to the bottom and remain there until them listeth to rise again at which time they unloose the stones and rise up at their pleasure And now to come closer to the explication of our difficult Problem there yet occurrs to me nothing more likely in order to it than what I have already mentioned in the Paper you will meet with about the Differing pressures c. And therefore it shall here suffice me to enlarge and by further Considerations and Experiments confirm what is there more summarily discoursed namely That the Phaenomenon may depend chiefly upon these two things the uniform pressure of the fluid Ambient and the robust texture of a humane body expos'd to this Pressure In one of the following * New Experiments about the differing Pressure of heavy Solids and Fluids Papers you will find examples of the great pressure that may be sustain'd unharm'd by such frail bodies as Eggs and thin Glasses that one would expect should be broken in pieces thereby provided the pressure be exercised by the intervention of an Ambient liquor as water And by the account elsewhere refer'd to of the Tadpole it seems highly probable that even that tender animal when it seem'd by some small diminution of the bulk to be every way a little compress'd inwards was put to no considerable or perhaps to any sensible pain or inconvenience since it seem'd to swim without any irregular motions which would in likelihood have insued if it had been much harm'd or incommodated Which example with those formerly pointed at may teach us that there may be a vast difference betwixt the resistance that a body can make when compress'd immediately by Solid bodies when in the compression every way ambient Fluids intervene Which you will the less admire if you consider that by reason of the grossness hardness or rigidness of visible Solid bodies the pressure can never be made every where so equally as by the parts of Liquors whose smalness which renders them singly invisible fits them to accommodate themselves far more closely and conveniently to all the superficial parts of the body immers'd in them and to have the force of the compressing body more uniformly distributed to them But because the Instances referr'd to are taken from bodies surrounded with water I will take two or three about the resistance of bodies to violently compress'd Air partly because those made in our Engine are wont to be perform'd with Air not condens'd but rarified or expanded
the incompetent resistance of the Air which he acknowledg'd to me he found by manifest tokens to be notably compress'd by the Superior water Which Relation from such a person does not only confirm our explication but likewise warrant us to doubt whether the Common Reports that are made concerning Divers be fit to be rely'd on without farther Examen and observation In the mean time I shall add two or three Experiments more to confirm the resistance that Animals may make to a great pressure when exercis'd by the mediation of a fluid Body And I the rather gave you an account of this way of making tryals because it may be also helpful to discover the resistances of inanimate Bodies whose Shape and Consistence we may choose and vary almost at pleasure to the pressure of totally or in great part ambient fluids And if I had been furnished with a tube wide enough and a quantity of Mercury great enough I might by the way have shewn you that whatever the Learned Doctor More is pleased to suppose that to Butter it self even as considerable a pressure may be so applyed as not to be able to make it yield thereunto For on this occasion I shall adde that I well remember that among other tryals to the same purpose I caused a piece of fresh Butter about the bigness of a small Hen-Egg to be brought to an irregular shape that if the compression were such as many would expect the long corners or solid angles being at least flatted the Butter might be reduc'd into a more capacious figure and less remote from roundness But though having put this lump of Butter into a Bladder almost full of fair water we proceeded both in the same brass Cylinder and much after the same manner that I employed about the Egg mentioned in the Fourth Experiment of the Tract of the Differing pressure of heavy Solids and Fluids yet I found that after the plugg had been loaded with a weight of Lead of above 50 pound neither I nor the Operator perceived the irregular figure of the Butter to be altered Nor was this the only tryal of this kind I made with the like success upon Butter though I dare not charge my memory with the Circumstances and therefore I shall without delay proceed to what I was about to recite concerning the Resistance of Animals We took then a common Fleshslie neither of the biggest sort of all nor of the least but of a middle size and having put it into the shorter leg of a bent Glass which we caus'd to be Hermetically seal'd at the end there was put in as much Mercury as fill'd that leg and a part of the other leaving little more than an inch of Air between the Quick-silver and the seal'd end that there might be room both for the Fly and the Condensation of the Air and then with a little Rammer fitted for the purpose we caus'd the Mercury in the open leg to be thrust against that in the seal'd leg which thereupon did necessarily croud the Air near the Fly into less room so that by our guess it was condensed into about a third part of the space which it possess'd before and which it regain'd when the Rammer was withdrawn And though this were done more than once yet not only the Fly was thereby not kill'd but not so much that appear'd as sensibly hurt and I perceiv'd her whilst she was pent up to move her legs and to rub them one against the other as 't is usual with that sort of Insects to do of their own accord in the free Air. Nor did I question but that if the Glass had not been inconveniently shap'd to admit the Rammer farther into it the Fly would have supported a far greater Pressure Another Experiment to the same purpose we try'd with Water instead of Mercury but whereas this last named liquor could neither wet nor drown our Fly for which reason I chiefly made choice of it the other did first wet its wings and soon after by a mischance drown it But first we had an opportunity to compress the Air into a third if not into a fourth part of its former dimensions and yet the Fly continued to move divers of her parts and especially her legs very vigorously as if nothing troubled her but her being as it were glu'd to the inside of the Glass by part of her wetted wings And this I hope will keep the Resistance of Divers to the Ambient water from seeming incredible since such Flyes were able to resist and for ought appear'd without harm or pain the pressure of the crouded particles of the Air though we guess'd this to have been as much compress'd by the force of the Rammer as it would have been by a Gylinder of water of 50 or between 50 and 60 foot high By which also we may be help'd to conceive how great a difference there is whether the same pressure be exercis'd by a solid or by a fluid Body For according to our estimate the pressure against the Body of the Fly was as great as if a slender pillar of Marble having the Fly for its Base and 18 or 20 foot in height had lean'd upon the little Animal which I presume you will easily think was more than enough to crush her to Death But because though the fore-going tryals are not like to be rejected by the skilful yet they require a somewhat dextrous and nimble Experimenter and leave something to his estimate I will subjoyn an Experiment more easie to be made and wherein the weight may be determined by Measure rather than Conjecture being made to be perpendicularly incumbent on the Fly or other Animal For the Experiment may be as well made on other Insects as Worms though some that I had provided chanc'd to miscarry before they came to be used We took then some ordinary black Flies such as use to haunt Butchers stalls in warm seasons of a middle size the length of the Body and Head of one Animal which for trials sake we measured being about three eights of an inch and having placed one of them with the head upwards that there was some distance left bewixt her and the sealed end of the Glass-tube 9 or 10 inches long we poured in Quick-silver very slowly and cautiously lest the force of so heavy a body acquired by the acceleration of its descent should more than the meer weight it self of the liquor oppress the Fly To this effect stooping the Glass very much towards the Horizon and letting the Mercury puss into the tube through a Funnel whose lower part was very slender that it might come down but by little and little we at length got in as much Mercury as the tube would receive and then holding it upright we watched whether the Fly would make any motions and finding that she did manifestly stir notwithstanding the incumbent Mercury we measur'd the height of the Mercurial pillar reaching from the middle of her
body to the top of the liquor and found it to be about eight inches and the Quicksilver being poured out the Fly appear'd to be so lively and vigorous that I doubted not but if we had had a longer Glass the Experiment had been much more considerable But when afterwards I was able to procure a better tube the season of Flyes being almost quite past I could scarce get any and those not brisk as they are wont to be in Summer But however we repeated the Experiment with one of the best we could take of the above-mentioned size and ordering the matter so that the Mercury incumbent on her for there was some beneath her appeared to be of a greater height than the formerly imployed tube was of we saw her move one or other of her little leggs divers times though the tube were held upright and therefore measuring the height of the Mercury above her we found it to amount to 16 inches and better and then freeing her from this pressure we observed that she immediately found her leggs again and moved up and down briskly enough but when she was loaden with 23 or 24 inches of the same Quicksilver though the liquor were soon after poured out she gave no signs of life which I suspected might happen not so much from her having been opprest by the greatness of her weight as from the great care of the Operator to let down the Mercury very obliquely and warily upon her And this I was the rather confirm'd in because having got an other Fly of about the same bigness though when she was at the bottom of the Quicksilver she seemed so comprest as not to have any motion we could take notice of yet upon her being taken out of the Glass she presently appeared to be alive by walking about and beginning to display her wings though the pillar of Mercury that had leaned upon her amounted to above 27 inches And I presume the success would have been much more considerable if the Experiment had been tryed in the Summer when these Creatures are brisk and lively and not as it was in the Winter besides that probably these little Animals were hurt or weaken'd by the violence that would scarce fail to be us'd in catching them and putting them into such a place and posture in the Glass as was required the actual coldness of the Quicksilver perhaps also making them somewhat torpid whilst it touched them so many ways And it must not be here omitted that a Fly that seemed but about half so big as one of those hitherto mentioned being well placed with some Mercury under it in a Glass-pipe held upright sustained a Mercurial pillar of somewhat above 25 inches and though she was not observed to move under so great a weight yet when once it was taken off she did not appear hurt much less crush'd to Death by it and probably would have escap'd under a much greater weight if the tube which was too large had not already imployed all the stock of Mercury we then had at hand But I do presume that what we did try will be available to our purpose since we see clearly that so small an Animal as a Fly may survive so great a pressure and that she could not only live but was able to move such long and slender Bodies as her leggs when she was pressed against by above 16 inches of Mercury and consequently by a weight equivalent to a pillar of water of above 18 foot and a half which being above 590 times her own length and according to the estimate our measure suggested many times more her own height so that a Diver 6 foot tall which is somewhat more than an ordinary mans stature to have as many times his height of water above him as our Fly might have had and yet have moved under it must dive at least in fresh water to near a hundred fathom which is a far greater depth perhaps by 5 or 6 times than for ought I could learn by inquiry the Divers either for Coral or Pearl are wont to descend And now Sir having tender'd you the likeliest conjectures that occurr'd to me about the solution of this difficult Problem I shall return to Doctor More and consider the objection he frames from the supposed insolubleness of it And on this occasion I shall have two or three things to represent to you The first is that there would be much more weight in what he objects if our Assertion of the gravitation of water in water were like the Principium Hylarchicum a meer Hypothesis advanc'd without any clear positive proof whereas our Doctrine is not only elsewhere directly proved by particular Experiments but by the very controverted one of the Tadpole to elude whose force so Ingenious a person is fain to flye to a Principle that to say here no more is not Physical And from this first of the things I lately mentioned I shall hasten to the second because it will require to be longer insisted on I shall then further represent that whatever power he is pleas'd to suppose at the bottom of the Sea to suspend the impression of the incumbent Water I think that supposition ought to give place if not to our former Ratiocinations yet to experience it self which shews there really is a great pressure exercis'd by the Water at the bottom of the Sea I remember that a friend of the Learned * Sir R. M. Doctors and mine who is so eminent a Virtuoso as to have been often President of the Royal Society related a while since to me that a Mathematical friend of his whom he nam'd having had an opportunity to try an Experiment I have in vain endeavoured to get tryed for me had the Curiosity to let down in a deep Sea a Pewter-bottle with weight enough to sink it that he might try whether any sweet Water would strain in at the orifice or any other part but when he had pull'd it up again he was much surpriz'd to find the sides of his Pewter-bottle very much compress'd and as 't were squeez'd inward by the Water I also not long since inquir'd of an observing Acquaintance of mine that has a considerable estate in America whether he had not try'd to cool his drink when he sail'd through the Torrid Zone by letting down the bottles to a great depth into the Sea and if he did in what Condition he found them when they were drawn up again To which he answer'd that he had several times employ'd that Expedient for the Refrigeration of his Drinks but was at first amaz'd to find the Corks with which the strong stone-bottles had been well stopt before so forcibly and so far thrust in that they could scarce have been so violently beaten in with a Hammer and 't was scarce possible to get them out And an other Ingenious Person that practises Physick in the Indies having the like Question put to him answer'd me that he had some while