from its being in nature's fcale very little lefs heavy than it need be, STATICS. to balance the preffure of the collateral water; but by this alfo, that if but a fingle grain be laid on, when it begins to rife, its afcent will be check'd, and hinder'd; which could not be done by the addition of fo inconfiderable a weight, if the wax, and the adhering metal, did not, even during their afcent, retain their former gravity; tho' that were fruftrated as to the act of defcending, or fo much as keeping their ftation, by the prevailing preffure of the collateral water. So that, fince the wax, and adhering metal amounted to confiderably above four thousand grains; it did, in the balance of nature, weigh, whilft afcending, not fo much as a four thoufandth part lefs than it did, whilft it was actually defcending. Upon the whole, then, Dr. More, had he throughly confider'd the matter, needed not have concluded the account of his experiment, as he does, by faying, "this is fo evident a demonftration against the gravity of the parts of water downwards; that unless it prove true, I fhall never af"fent to any reasoning of my own, for the future, nor to that of any other man whomsoever." But, I hope, he will confider, as well as I, that a man may be very happy in other parts of learning, who has had the miffortune to mistake in hydrostatics; a fcience which very few scholars have been at all vers'd in. As for the last experiment in my hydroftatical paradoxes, the Doctor Water made to feems to fufpe&t the matter of fact; or, fuppofing it true, accounts for it Support a body of a much greater from his hylarchic principle, and the interpofition of the valve of the inftru-Specific gravity than itself. ment; but what confiderable intereft the imaginary retraction of the valve, or the air itself, can have in this phenomenon, I confefs I do not difcern: for, I think, the experiment would fucceed, when try'd in vacuo, tho' all the atmospherical air were annihilated. However, to avoid all miftakes, and difputes, that may arife upon account of the valve employ'd in our experiment; a quantity of quick-filver, being, by fuction, rais'd into a very flender glass-pipe, whofe upper orifice was ftopp'd with the finger, to keep the mercury from falling out; we thruft the open end of the pipe, with the mercury in it, into a deep glafs of water, till the little cylinder of mercury had, beneath the furface of the water, attain'd to a depth, at least fourteen times as great as the height of the mercurial cylinder; when, the finger being removed from the upper orifice, the glafs-pipe will be open at both ends, and nothing can hinder the quick-filver from falling to the bottom, but the refiftance of the cylinder of water that is under it; which cylinder can refift but by virtue of the weight, or preffure, of the ftagnant water above it, tho' but collaterally placed: yet this water being, by the pipe, whofe upper part is higher than the furface of that, and acceffible only to the air, kept from preffing against the mercury any where but at the bottom of the pipe; and being about a fourteenth part of the weight of an equal bulk of mercury; is able, at that depth, to make the fubjacent water prefs upward against the mercury, which is but a fourteenth part as high as the water is deep, with a force equal to that of the gravity, wherewith the mercury tends VOL. II. Zz down it STATICS. downwards. The cafe of di And, to manifeft that this phenomenon depends merely upon the equilibrium of the two liquors; if you gently raife the lower end of the pipe towards the furface of the water, this liquor, being not then able to exercife fuch a preffure as it could at a greater depth, the mercury preponderating, will fall out to the bottom of the tube. But if, when the quick-filver is at the first depth, instead of raifing the pipe, you thruft it down farther under the water; the preffure of that liquor against the mercury, increasing with its depth, will not only fuftain the mercury, but impel it up in the pipe to a confiderable diftance from the lower orifice, and keep it about the fame diftance from the furface of the water, which is laterally above it. And this experiment may not only ferve for the purpofe for which I here alledge it; but, alfo, if duly confider'd, and apply'd, very much illuftrate and confirm the explanation, formerly given, of the feemingly fpontaneous afcent of the clogg'd fucker in our exhausted air-pump. The laft argument which the Doctor urges against the gravitation of vers, with rewater, in its proper place, as they fpeak, is deduced from what happens to gard to the Jure of the wa- divers, who, in the midft of the fea, tho' falt-water be much heavier than ter they futain, fresh, do not find themselves compreffed by the vaft load of the incumbent at great depths. water. But if obfervations about diving were made by philofophers, and mathematicians, or, at leaft, by intelligent men; we should, I do not doubt, have accounts of it, very different from the current reports. A learned phyfifician, of my acquaintance, upon diving leifurely, perceived a conftriction of his thorax, by the action of the furrounding fea-water. A Spanish prelate, who liv'd long in America, fpeaking of the Indians, employ'd by their inhuman mafters in fifhing for pearls, tells us, it is impoffible that men fhould live for any long feafon under the water, without taking breath; fo that they die commonly thro' vomiting blood, "and of the bloody flux.' And a general of the English in the East-Indies, fent on an embaffy to the emperor of Japan, fpeaks thus of fome female-divers he met with in his voyage. "All along the coaft, and fo up to Ozaca," fays he, we found women-divers, who lived, with their houfhold and family, in boats upon the water. Thefe women," he fays, "would catch fish by diving, which they miffed by net and line, and that in eight fathoms depth. "Their eyes, by continual diving, grow as red as blood; whereby a diving woman is diftinguifhed from all others." However, the reafon why fo little damage is fuftain'd by diving, feems, in my opinion, owing to the uniform preffure of the furrounding fluid, and the robuft texture of a human body*. "Tis remarked by Sir Ifaac Newton, that fince fluids, in preffing bodies immerfed in them, do not change the external figures thereof, they will not change the fituation of the internal parts among one The another; and, therefore, that if fenfation proceeds from the motion of the parts of animals; fluids will not damage the anımals immerfed therein, nor excite any fenfation in them, farther than as their tender bodies. The fwims of fmaller fish appear very unable to refift compreffure, being STATICS. much more thin and delicate to the eye, than a piece of fine Venice paper; yet having caused one of these bladders, above an inch in length, and pro-a fluid sustain'd Vaft presures of portionably wide, to be taken out of a roach, and anointed with oil, to by weak and keep it fupple, and preferve it from being pierced, or foften'd, by the water; and having, by a weight of lead, faften'd to the neck of it, let it down to the bottom of a cylindrical tube of water, fealed at one end, and made large, and about fifty-fix inches long; we could not perceive that, by the weight of all the incumbent water, it was manifeftly comprefs'd, or that it discover'd the leaft wrinkle, or other depreffion of that very thin membrane, tho' fill'd but with air. And this trial was made more than once with the fame fuccefs. Yet that this proceeded rather from the ftrength of the bladder, that was able to refift the weight of a taller pillar of water, than from the levity of water in the upper part of the tube on that in the lower, we fhew'd, by prefently letting down a mercurial gage, by a ftring, to the bottom of a tube: for the weight of the incumbent water forced up fome of the mercury out of the open leg of the fyphon into the feal'd one; and, confequently, comprefs'd the air included there: and the uncompreffed air, being three inches and in length, we judged it, at the bottom of the tube, to be about impell'd up by the intrufion of the mercury. And, to fatisfy myself, and others, that if the incumbent water had been heavy enough, it would, vifibly, have affected the bladder, in fpite of any Principium hylarchicum; we funk it in a cryftal glafs, that had a long cylindrical neck, and was exactly fitted with a ftopple; then a competent quantity of air being left above the water, the stopple was warily, and by degrees, thruft down; and fo, leffening the capacity of the glass, compreffed the air that was next it, and, by the intervention of that, the water under it. And tho' there did not, upon a flight compreffion of the outward air, appear any fenfible effect upon the bladder that was at the bottom of the water; yet, upon a farther intrufion of the ftopple, the preffure being increased, the immerfed bladder discover'd two confiderably deep wrinkles, that prefently disappear'd upon drawing up the stopple; which, being thruft in again, the depreffions were again to be feen on the fwim. And, having convey'd a mercurial gage into the fame glafs, we eftimated, by the condenfation of the air in the feal'd leg of it, that the bladder had been exposed to a preffure equal to that of a column of about forty feet of water. This may leffen our wonder, that bodies, of fo firm a texture as those of lufty men, fupport the preffure of the water at fuch depths as divers ufually remain; fince we fee what refiftance can be made by fo exceeding bodies may be condenfed by compreffure. Newton. Princip. p. 264, 265. And Borelli, having fhewn, that a quantity of fand, contain'd in a very hard or rigid veffel, cannot poffibly be divided, or entred, by a wedge; and that water, in like manner contained in a bladder, every way equal- STATICS. thin and delicate a membrane, diftended only with the air, in comparison of the ftrong membranes and fibres of a man, fill'd, befides air, with more firm parts. 'Tis alfo confiderable, what great weights may be fuftain'd in the air, by fuch fibres or tendons, and by other fibres interwoven into membranes, in comparison of what an ordinary man would expect. And, not only upon account of the ftable parts of a human body, but of the fpirits too, it may refift very violent preffures of a fluid, without any manifeft contufion, or dislocation of parts, or even fenfe of pain; as appears from the great effects which gufts of wind have upon trees, houfes, &c. tho' a man will withstand the impetuofity of fuch a ftrong wind, and walk directly against it, by virtue of the vigour of his muscles and fpirits, without being thrown down, or bruifed, by fo violent a current of air, and without fo much as complaining of pain; and this, tho' the wind that beats against him, acts as a ftream, and does not uniformly comprefs him, but invade only the fore-part of his body. Thus, alfo, in the lifting up of heavy weights by lufty men, we may fee the flender tendons of the hand loaded with an hundred and fifty pounds, or more, without having their fibres fo far compreffed, or ftretched, as to make the perfon complain of pain. A human body, therefore, is an engine of a much firmer ftructure, than mere fcholars ufually take notice of. And, I doubt, whether, if the structure of a man were not confiderably firm, he could, efpecially in a deep fea, fupport the preffure of the water, tho' not immediately apply'd, without pain. For, having, feveral times, convers'd with a man who got his living by diving for fhip-wreck'd goods; he affured me, that, when he ftay'd at a confiderable depth, as ten or twelve fathoms, under the furface of the fea, he felt a great pain in both his ears, which often put him to fhifts to leffen it; and this, by his manner of defcribing it, I concluded, arofe from the incompetent refiftance of the air, which he found, by manifeft tokens, to be greatly compreffed by the upper water. This relation, from fuch a perfon, not only confirms our explanation, but likewife warrants us to doubt whether the common reports that are made concerning divers, ought to be rely'd on, without further examination. We took a common flesh-fly, of a middle fize, and having put it into the fhorter leg of a bent glafs, which we caufed to be hermetically fealed, we added 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-filver, and the feal'd end, that there might be room both for the fly, and the condenfation of the air; and then, with a little rammer, fitted for the purpofe, we caus'd the mercury, in the open leg, to be thrust against that in the feal'd one; which neceffarily crowded the air, near the fly, into lefs room; fo that it feem'd condens'd into about a third part of the fpace which it poffefs'd before, and which it regain'd, when the rammer was withdrawn and tho' this were done more than once, yet the fly appear'd not fenfibly hurt; and I perceiv'd her, whilft fhe was pent up, to move her legs, and to rub them one against the other, as 'tis ufual with that fort of infects in the free air. Another Another experiment, to the fame purpose, we made with water; tho' this STATICS. wet the wings of the fly, and foon after, by mifchance, drown'd it: but we had, firft, an opportunity to comprefs the air into a third, if not a fourth part, of its former dimenfions; yet the fly continued to move feveral of her parts, and, efpecially her legs, very vigorously; as if nothing troubled her, but being, as it were, glued to the infide of the glafs by her wetted wings. And this, I hope, will keep the refiftance of divers, to the furrounding water, from feeming incredible; fince fuch flies were able to refift, and, for ought appear'd, without harm, or pain, the preffure of the crowded particles of the air: tho' we guefs'd it to have been as much comprefs'd by the force of the rammer, as it would have been by a cylinder of water, of between 50 and 60 feet high. Hence, too, we may be affifted to conceive, how great a difference there is, whether the fame preffure be exercised by a folid, or by a fluid body. For, according to our eftimate, the preffure against the body of the fly was as great, as if a flender pillar of marble, having the fly for its bafe, and 18, or 20 feet in height, had refted upon the little animal. We alfo took fome ordinary black flies, of a middle fize; and having placed one of them, with the head upwards, and left fome distance betwixt her and the feal'd end of the glafs tube, we pour'd in quick-filver very flowly, and cautiously, left the force of fo heavy a body, acquired by its velocity in the fall, fhou'd, more than the mere weight of the fluid, opprefs her: at length we got in as much mercury as the tube would receive; and then, holding it upright, we watch'd whether the fly would make any motions; and finding that fhe did manifeftly ftir, notwithstanding the incumbent mercury, we meafur'd the height of the mercurial pillar, reaching from the middle of her body, to the top of the fluid, and found it to be about eight inches; and the quick-filver being pour'd out, the fly appear❜d very lively, and vigorous. We repeated the experiment with one of the beft flies we could take, when their feafon was almoft over, and of the fame fize with the former; when, ordering the matter fo, that the mercury incumbent on her, appear'd to be of a greater height than that of the tube before employ'd, we faw her move one, or other of her legs, feveral times, tho' the tube was held upright; and therefore, meafuring the height of the mercury above her, we found it to amount to above fixteen inches; then freeing her from this preffure, we obferv'd, that fhe immediately found her legs again, and moved, up and down, briskly tho, when she was aftewards opprefs'd, with 23, or 24 inches of the fame quick-filver, fhe gave no figns of life. But having got another fly, of about the fame bignefs; tho', when she was at the bottom of the quick-filver, fhe feem'd fo comprefs'd as not to have any motion, yet, upon being taken out of the glafs, fhe prefently difplay'd her wings; tho' the pillar of mercury, that prefs'd upon her, amounted to above 27 inches. Another |