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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 fol∣lowing conclusion: Haec tam lucu∣lenta Demonstratio contra Gravita∣tionem particularum aquae inter se quamvis junctae situlae fundum ur∣geant, si non sit vera atque solida, e∣quidem nec mei ipsius nec ullius un∣quam mortalis in posterum ratiocini∣is 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 mis∣fortune 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 em∣braced.
To the foregoing Argument the
Doctor, though he declares he thinks it needless, adds in the 5th Para∣graph another, taken from the Last experiment of my Hydrostatical Pa∣radoxes, by which he ingenuously ac∣knowledges, that I seem at first sight to have demonstrated what I pretend to, about the gravitation of the up∣per parts of stagnant water upon the lower. And I am sorry that I can∣not in return acknowledge, that his objection at first sight seem'd to me a cogent one: For, neither at the se∣cond nor third perusal can I clearly discern where his Ratiocination lyes, supposing it to be meant for an an∣swer to my experiment. And though I consulted with some Learned Mem∣bers of the Royal Society, whereof two are Mathematicians, and one his particular friend; yet they all con∣fess'd he had not sufficiently ex∣plain'd himself on this occasion, nor
could they shew me to what argumen∣tation I might properly direct my reply. Only one of the Doctors Correspondents, having seriously per∣us'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 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 tan∣gat Superficiem V. W, vis retractionis Aeris ita augetur ut etiam ponderis ap∣pensi superadditam depressione•• su∣peret. Videtur igitur quasi quaed••m sursum-suctio Aeris in tubo contenti, & conformis ac contemporanea aquae compulsio in obturaculum, quo tam fir∣miter in os valvulae comprimitur, ibi∣que cum appenso pondere sustentatur. What considerable interest the sup∣posed, 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 suc∣ceed when tri'd in vacuo, although all the Atmosphetical Air were anni∣hilated. But if I mistake the Doctors
meaning I am to be excused, since I do it not willingly, and his own ob∣scurity has been accessary to it. Nor am I very apprehensive of being una∣ble to defend my account of an expe∣riment, 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 curi∣ous Persons, several of which were sufficiently indispos'd to admitt it.
And to avoid all mistakes and dis∣putes that may arise (which I think they must do needlessly) upon the score of the Valve imploy'd in our Ex∣periment, I shall remind you of an∣other, that I remember I have some times shew'n you and divers other Virtuosi, though I remember not whe∣ther I have mention'd it in any of my publish'd writings. The Summ of this tryal is, that an arbitrary Quan∣tity 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 compe∣tently deep glass of water till the little Cylinder of Mercury have, be∣neath the surface of the water, at∣tain'd to a depth, that is at least 14 times as great as the Mercurial Cylin∣der has of height. For then, the fin∣ger 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 resi∣stance of the Cylinder of water, that is under it, which Cylinder can re∣sist but by vertue of the weight or pressure of the stagnant water that is superior to it, though but collateral∣ly plac'd above it: And yet this
water being by the pipe, whose up∣per 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 up∣ward 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 de∣pends meerly upon the Aequilibrium of the two liquors; if you gently raise the lower end of the pipe to∣wards the surface of the water, this liquor, being not then able to exer∣cise such a pressure as it could at a further and greater depth, the Mer∣cury 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 consi∣der'd and applyed, may very much both illustrate & confirm the Expli∣cation formerly given of the seeming∣ly 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 Ri∣vers, 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 pres∣sures of an ambient fluid will goe a great way towards the solving of this Difficulty, you will find, by the Ex∣periments and considerations you will meet with in the following Papers, to which, for that reason, I referr you. And though the Doctor in this same Paragraph objects, Tametsi haec pressio aequalis sit, ni∣hil tamen impedit quò minùs subtiliores partes corporis magisque fluidas expri∣mat & 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 is∣sue, 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 mi∣nute 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 wa∣ter, seem'd a little, though but a little, to shrink.
But that we may the more distinct∣ly 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; 'twill 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 some∣what demanded. For, in the Que∣stion 'tis taken for granted, that Di∣vers, 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 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 op∣pressed and crush'd to death by the pressure of the Incumbent and Am∣bient water. And the second, why at least he should not be made sensibly to feel it by suffering some conside∣rable inconvenience from it.
In answer to the first of these Que∣stions, you will easily perceive, that divers things may be pertinently ap∣plyed, that you will meet with in the following Paper, to shew the differ∣ence 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 Trea∣tise, by the experiment
of a little Tadpole, which being, toge∣ther with the water it swam in, inclu∣ded 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 ha∣ving made use of it with a Scheme to explain it in his 16th. Paragraph; it will be fit for me to consider his Ob∣jection. 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 Hy∣larchico 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 sub∣joining the following passage; Ne∣que emim sequitur ex earum contactu quod premant se invicem, quandoqui∣dem particulae, uti fit in duris Corpo∣ribus, in unum coalescere possunt & ta∣men non mutuò se premere; (Where∣in are some things that might be question'd if it were necessary;) He thus pursues his Discourse: Cùm verò hîc particulae aquae si omninò pre∣merent se invicem, pressura in Gyri∣num, columnae aqueae, ducentos vel tre∣centos pedes, aeneae verò, plus viginti vel triginta pedes altae, pressionem ad∣aequaret, 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 incumbente••n omnia viscera tam tenellae Gelatinae no•• esse elisuram. Notwithstanding which al∣legation I am apt to think, you will judge the Argument from this expe∣riment to be more probable on my side than on the Doctors. For there being in our case an animal, exceed∣ingly 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 pre∣tend to have given a pertinent in∣stance, that a Diver may be at a con∣siderable 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 Inco∣lumity of the Tadpole is, that the pres∣sure or contrusion of the particles of the water against one another is hin∣der'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 ex∣ternal force duly and yet ineffectu∣ally applyed to press to Death by means of the water the animal swim∣ming in it;) but that this Mechani∣cal force was suspended or made ineffectual by some invisible and im∣material Agent, is but the Doctors Hypothesis, and a thing, which, whe∣ther 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 en∣quiry, I am now entring upon, as well
sometimes to employ and inlarge par∣ticulars already mentioned in the last of the following Papers, as often∣times to strengthen them with new ones. And I shall also for a while suspend my difference with the Do∣ctor, and addressing my self to you, who, I am sure, will allow me that water weighs in water, propose, ac∣cording to my custom, not as a Dog∣matist, but as an Inquirer, some par∣ticulars, 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 expli∣cated 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 bo∣dies 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 concern∣ing 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 ge∣nerally 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 obser∣vations 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 per∣haps have an account of what hap∣pens to men under water differing enough from the common reports.
You will in one of the following Pa∣pers find mention of a Learned Phy∣sician 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 deplo∣rable condition of those wretched In∣dians that were employed by their inhumane Masters about the fishing for Pearls, gives us this account of them: 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 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: 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 dis∣eases
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 cer∣tain, 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 inconveni∣ently, 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 pro∣duc'd in the nervous and membra∣nous parts, occasioned by the com∣pression 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 hin∣dering 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 Lear∣ned and Intelligent men, when pre∣possest (as these Common Divers usually are) with the vulgar opi∣nion about the Non-gravitation of Water and Air in their natural places,
do almost always refer an experiment of my Engine to Suction, which is indeed the effect of the pressure of the Ambient, (as I have † elsewhere clear∣ly 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 'twas not altogether without cause, that I complain'd of the incompetency of the History of what Divers feel under water; espe∣cially at great depths, where this want of information may be more consi∣derable: For, as far as I have yet learnt by perusing Voyages and en∣quiring
of Travellers of my acquain∣tance, the places, where they are wont to dive for Pearl, are but moderately deep, and indeed shallow in compa∣rison 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, pos∣sibly the accounts would be different enough to render doubtful or to cor∣rect the received opinions about the conditions of Divers at the bottom of the Sea. For, I remember that a cre∣dible eye-witness, who, (if I mistake not) was the Intelligent Oviedo, speaking of the Pearl-fishing on the American Island of Cubagna, has a∣mong 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 vio∣lence 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 ex∣plication 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 fur∣ther Considerations and Experiments confirm, what is there more summarily discoursed; namely, That the Phaeno∣menon
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 follow∣ing. 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 ex∣pect 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 com∣press'd inwards, was put to no consi∣derable (or perhaps to any sensible) pain or inconvenience, since it seem'd
to swim without any irregular mo∣tions, 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 ambi∣ent 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 ren∣ders 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 beyond its usual con∣sistence; and partly, because it will not be deny'd, that the corpuscles of Air may be really comprest or thrust against one another, since 'tis 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 anoin∣ted 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 Hy∣drostatical 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 Mercu∣rial-Gage as is describ'd, & often men∣tioned 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 com∣press'd the air included there, which though it were not very much, yet it was very manifest. For the un∣compress'd Air being 3 inches and ⅝ in length, we judg'd it at the
bottom of the tube about ⅝ by the in∣trusion of the Mercury that was im∣pell'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 e∣nough, 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 Cy∣lindrical too, that 'twas 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 wa∣rily 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 compres∣sion
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, de∣pressions 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 con∣densation 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 de∣licate a membrane stuff'd only with air, in comparison of the strong mem∣brans 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, inter∣woven into membrans, in compari∣son 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 con∣rusion or dislocation of parts, but
without any sense of pain; which I suppose you will grant me, if, consi∣dering 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 impe∣tuosity 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, Car∣riers 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, with∣out having their fibres so far com∣press'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 con∣siderably (though not perhaps e∣qually) firm, he would, especially in a deep Sea, be able to bear the pres∣sure of the water, though not imme∣diately 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 Ship∣wrack'd goods, he answer'd me, when I ask'd him whether he felt any pecu∣line pressure against the Drums of his Ears, which are membranes ••••t so well back'd as those of other parts; that when he stai'd at a consi∣derable 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 the incompe∣tent resistance of the Air, which he acknowledg'd to me he found by ma∣nifest tokens to be notably com∣press'd by the Superior water. Which Relation from such a person does not only confirm our explication, but like∣wise warrant us to doubt, whether the Common Reports that are made concerning Divers be fit to be re∣ly'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 ac∣count 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, what∣ever the Learned Doctor More is plea∣sed 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 compres∣sion were such as many would ex∣pect, the long corners or solid angles being at least flatted, the Butter might be reduc'd into a more capa∣cious 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 mention∣ed 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 Flesh∣slie, 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, lea∣ving 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 Condensa∣tion 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 Ram∣mer 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 'tis 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 ap∣pear'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 esti∣mate, 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-go∣ing tryals are not like to be rejected by the skilful, yet they require a somewhat dextrous and nimble Ex∣perimenter, and leave something to
his estimate, I will subjoyn an Ex∣periment more easie to be made, and wherein the weight may be deter∣mined by Measure rather than Con∣jecture, being made to be perpendi∣cularly 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 pla∣ced one of them with the head up∣wards, 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 acce∣leration of its descent, should more than the meer weight it self of the li∣quor 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 vi∣gorous,
that I doubted not, but if we had had a longer Glass, the Experi∣ment had been much more consider∣able. 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 Sum∣mer. 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,) appear∣ed 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 free∣ing her from this pressure, we obser∣ved,
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 com∣prest as not to have any motion we could take notice of, yet, upon her being taken out of the Glass, she pre∣sently appeared to be alive by walk∣ing about and beginning to display her wings, though the pillar of Mer∣cury,
that had leaned upon her, a∣mounted 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 wea∣ken'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 re∣quired; the actual coldness of the Quicksilver perhaps also making them somewhat torpid, whilst it touch∣ed 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 un∣der it, in a Glass-pipe held upright, sustained a Mercurial pillar of some∣what
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 Mer∣cury 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 pres∣sure, 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 (consequent∣ly) by a weight equivalent to a pil∣lar 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 (per∣haps 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 dif∣ficult Problem; I shall return to Do∣ctor More, and consider the objection, he frames from the supposed insolu∣bleness of it. And on this occasion I shall have two or three things to re∣present to you.
The first is, that there would be much more weight in what he ob∣jects, if our Assertion of the gravi∣tation of water in water were, like the Principium Hylarchicum, a meer Hy∣pothesis 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 In∣genious 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 sup∣pose at the bottom of the Sea to sus∣pend the impression of the incum∣bent Water, I think, that supposition ought to give place, if not to our for∣mer
Ratiocinations, yet to experi∣ence 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 Doctors and mine, who is so eminent a Virtuoso as to have been often President of the Royal So∣ciety, related a while since to me, that a Mathematical friend of his, whom he nam'd, having had an op∣portunity to try an Experiment, I have in vain endeavoured to get try∣ed 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 Wa∣ter 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 'twere, 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 a∣maz'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 'twas scarce possible to get them out. And an other In∣genious Person, that practises Physick in the Indies, having the like Que∣stion put to him, answer'd me, that
he had some while since had the Cu∣riosity 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 per∣haps 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 'twas 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 Contro∣versie, whether Nature do any thing
ob fugam Vacui, but only answer, that I cannot find by the Relations of the Divers or otherwise, that 'tis ever so cold at the bottom of the Sea, as 'tis frequently above ground in Winter, when great Fishes are com∣monly said to return to the deep parts of the Sea for warmth, and yet in the sharpest Winters I never ob∣serv'd Corks to be driven in by the cold of the Ambient; nay, I pur∣posely tryed with a Frigorifick mix∣ture, that very intense degrees of cold, such as would quickly freez many Liquors, would not occasion the breaking of thin bubbles of Glass pur∣posely 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 Suc∣cedaneum to a solid stopple. Taking then a Glass-Vial, furnished with a (somewhat long) Cylindrical neck, whose Cavity was large in propor∣tion 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 Mer∣cury. 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 in∣cluded Air might be brought to the Temperature of the surrounding Li∣quor,) and by a string let further down into the same Glass-vessel fill'd to about two foot in height, the pres∣sure 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 instru∣ment 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 con∣firm it, I have deliver'd in another Discourse.
And here I shall sub∣joyn what very opportunely occurr'd to me since the writing of the last page. Meeting casually with an In∣genious Mechanician, (whom you will find I have elsewhere mentioned) that devised a suit of cloaths and other accommodations, (where∣in 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) whe∣ther he felt not the pressure of the water against his breast and belly, to which he answer'd me (more cir∣cumstantially than he had before) that when he was about 4 or 5 yards under water, though but in the Ri∣ver 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 ne∣cessitated 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 pres∣sure 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 ob∣noxious, 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 am∣bient water endeavoured to press him & his Diving suit every way inwards. Whether the coldness of the water had any interest in this Phaenome∣non, I particularly enquired of the Engineer; but he replyed, that by reasion of the tightness of his Di∣ving suit or instrument, the warm steams of his body that were pent in, and other concurring circum∣stances 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 Con∣firmation of our Hypothesis. In the mean time, the things already recited, together with the preceed∣ing
Experiments, may well suffice for our present purpose. For, by what hath been said it appears, that Wa∣ter does actually press against bo∣dies, whether specifically lighter or heavier than it self, placed under water, and that this pressure in∣creases with the height of the water above the immersed Bodies. And this being so, it is not more ne∣cessary 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 gi∣ving us partial informations, will have much more weight with unpro∣judiced persons, than the suspicious and sometimes disagreeing accounts of ignorant Divers, whom preju∣dicate
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 con∣versant in Hydrostaticks, are wont to think it very difficult, if not im∣possible, to conceive, how so weak a thing, as they fancy an Animal to be, should avoid the being op∣press'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 re∣member, how little they would have believed, that there is so great a difference, as we have by the Tad∣pole, the Fly and other instances, shewn there really is between the pressure of Solid and of Fluid bo∣dies,
will, I presume, be apt to think it fit, that, if for want of a suffici∣ent 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 bo∣dy; we should, to remove those re∣maining 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 Crea∣ted Agent, to explain clearly whose manner of working would be a much more difficult Task, than the solu∣tion 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 Hy∣pothesis 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. Chap∣ter the Doctor is pleased to spend divers pages in the Explication of divers of my Hydrostatical Phae∣nomena by the Agency of that in∣corporeal Director, that he calls Prin∣cipium Hylarchicum; yet since these Explications of his are rather at∣tempts to accommodate the Phae∣nomena to the Hypothesis, than ob∣jections directly levell'd against my Solutions, I shall altogether for∣bear 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 Me∣chanical solutions of the Experi∣ments 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 para∣tum ad movendum quo∣quoversum materiam pro data occasione; yet since he also tells us, Quod parti∣culae molis corporeae sive stabilis sive fluidae à Prin∣cipio Hylarchico in unam aliquam par∣tem omnes junctim urgeri possunt & premi, quamvis singulae singulas in nul∣lam partem premant, quodque pro mag∣nitudine molis major minorve totius fit pressio; and that the force by which it endeavours to keep the E∣lements in their true and natural
Consistence, though it be very great, is not invincible : 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 Crea∣ture, which 'tis like the Peripate∣ticks and divers other Philosophers may think less qualified for the Pro∣vince assign'd it, than their fuga Vacui, whereto they ascribe an Un∣limited power to execute its Fun∣ctions. I leave it therefore to you, Sir, to judge which of the two ways, of explicating an Hydrostatical Phae∣nomenon, the Learned Doctors, or that which I have made use of, re∣lishes 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 account∣ed for it, if, by the shape, size, mo∣tion, &c. of the Spring-wheels, ba∣lance 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 con∣vince 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 Prin∣cipium Hylarchicum, but only to inti∣mate, 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 introdu∣cing any precarious Principle; espe∣cially experience having shewn, that the generality of Heathen Philoso∣phers 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 no∣thing more to say, but that I would not have any thing that I have said misconstrued to the Learned Doctors prejudice. For 'tis 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 war∣rant 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 ten∣derness 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.
The Author means the New experiments of the differing pressure of hea∣vy solids, & fluids,
The Author points at the Appendix to the Hydrostatical Paradoxes.
See Purch. Tom. IV. Lib. 8. p. 1587.
Purch. Tom. I. Lib. 4. C. 1.
The reason of which experiment may be gathered from the 4th. Chap∣ter of the Author's long since publish'd Defence against Li∣nus.
In a Paradox about Suction.
New Experiments about the differing Pressure of heavy Solids and Fluids.
Sir R. M.
See the Pa∣radox about Suction.
In the Tract of the Differ∣ing Pressure of heavy Solids and Fluids.
Page 175.
Page 167.
Pag. 167.