cilitated. Then the upper orifice of the cylinder was very carefully ftop'd; PEUMATICS, the valve being likewife fhut, with its ftopple well oiled, after the fucker had been again impell'd up to the top of the cylinder. To the former weight we now added a hundred and twelve pounds, which forcing down the fucker, though but leifurely, we took off the 28 pound weight, and hung on, instead of it, fourteen pound; but found that, with the reft, unable to carry down the fucker. And to fatisfy ourselves it was the refiftance of the ambient air, that hinder'd the defcent of fo great a weight; after we had try'd, that upon unftopping the valve, and thereby opening an access to the external air, the fucker would be immediately drawn down, having forcibly deprefs'd the fucker, to the bottom of the cylinder, and then faften'd weights to the iron, the preffure of the external air, finding little refiftance, in the cavity of the cylinder, prefently began to impel the fucker, with the weights that clogg'd it, towards the upper part of the cylinder, till fome fuch accidental impediment, as we formerly mention'd, check'd its courfe; and when that was remov'd, it would continue its afcent to the top. And tho', poffibly, there might remain fome particles of air in the cylinder, after the fucker was drawn down; yet the preffure of a cylinder of the atmosphere, fomewhat lefs than three inches in diameter, uncomprefs'd, not only fuftain'd, but drove up a weight of a hundred and odd pounds: for, befides the weight of the whole fucker itself, which amounts to fome pounds, the weights annex'd to it, made up a hundred and five pounds; yet all this falls fhort of the weight juft faid to be fufpended, by the refiftance of the air, in the cavity of the cylinder. This experiment was made in the winter, the weather neither frofty nor rainy, about the change of the moon; and at a place whofe latitude is about 51 degrees and a half: for, perhaps, the force, or preffure of the air, may vary, according to the feafons of the year, the temperature of the weather, the elevation of the pole, or the phafes of the moon; any of them feeming able to alter either the height, or confiftence of the atmofphere. And therefore, it would not be amifs, if this experiment were try'd carefully, at feveral times and places, with variety of circumftances. It might, alfo, be try'd with cylinders of feveral diameters, exquifitely fitted with fuckers; that we might know what propoption feveral pillars of the atmosphere, bear to the weight they are able, to fuftain, or lift up; and confequently, whether the increase, or decrease of the refiftance of the ambient air, can be reduced to any regular proportion, to the diameter of the fuckers. Thefe, and other experiments, which may be made with this cylinder, might, moft of them, be more exactly try'd by the Torricellian tube; if glafs could be blown, and drawn perfectly cylindrical. Here we may obferve, that as many other phenomena of our engine, The nature of fo efpecially the two laft experiments, feem to fhew the nature, or caufe of fuction. It's true, indeed, in fucking, we commonly use fome manifeft endeavour, by a peculiar motion of our mouths, chefts, &c. yet it appears not how the upper-part of the emptied cylinder, that remains at reft all the while, or any part of it, endeavours to draw the deprefs'd

L112

fucker,

Suction

PNEUMATICS. fucker, and the annex'd weights to it; tho' fuch as behold the afcent of the fucker, without confidering the cause of it, readily conclude it to be rais'd by fome fecret thing, that powerfully fucks or attracts it. Whence it feems not abfolutely neceffary to fuction, that there be in the body, which is faid to fuck, an endeavour, or motion in order thereto; but rather that fuction may be reduced to trufion, and its effects afcribed to a preffure of the neighbouring air, upon the bodies contiguous to that which is faid to attract them. To object here, that fome particles of air, remaining in the emptied cylinder, attracted this weight, to obviate a vacuum, is to no purpofe; unless it can clearly be made out, by what grappling inftruments the external air could take hold of the fucker; how fo little of it obtain'd the force to raise fo great a weight; and why, upon letting a little more air into one of our evacuated veffels, the attraction is much weakned. For that ftill there remain'd in the exhaufted cylinder many little empty spaces, may appear by the great violence wherewith the air rusheth in, if it be permitted to enter. In the next place, these experiments may teach us, what to judge of the vulgar axiom, That nature utterly abhors a vacuum; fo that no human power is able to make one And vacuity. in the univerfe. For, if by a vacuum we understand a place perfectly free from all corporeal fubftance, it may be plausibly maintain'd, that there is no fuch thing in the world. But the generality of the plenifts take not the word in fo ftrict a fenfe. For when they alledge, that by fucking water thro' a long pipe, the liquor, contrary to its nature, afcends into the mouth, only to fill up that space, made by the dilatation of the breaft and lungs, which would, otherwise, in part, be empty; and when they tell us, that the reafon why in a gardener's watering-pot, conically fhaped, and filled with water, none falls thro' the numerous holes at the bottom, whilft the orifice at the top, is clos'd; muft be, that if, in case the water should defcend, the air being unable to fucceed it, there would be left a vacuum at the upper part of the veffel, they feem to mean by a vacuum, any space here below, that is not fill'd with a vifible body, or, at leaft, with air, tho' it be not quite deftitute of all bodies whatsoever.

Taking then, a vacuum in this vulgar and obvious fenfe, the common opinion about it feems liable to feveral exceptions, whereof fome of the chief are fuggefted by our engine.

It feems unintelligible, how hatred, or averfion, which is a paffion of the foul, can either for a vacuum, or any other object, be fuppofed in water, or any inanimate body, which cannot be prefum'd to know when a vacuum would enfue, if they did not attempt to prevent it; nor to act contrary to what is moft conducive to their own particular prefervation, for the good of the univerfe. The meaning, therefore, of this metaphorical expreffion feems to be, that by the wife author of nature, the univerfe, and the parts of it, are fo contriv'd, that it is as hard to make a vacuum in it, as if they ftudiously confpired to prevent it.

But our experiments teach, that this fuppofed averfion of nature to a vacuum, is merely accidental, or confequent upon the weight, fluidity, or

fluxility of the bodies here below; and, perhaps, principally of the fpringPEUMATICS of the air, whofe conftant endeavour to expand every way, makes it either rufh, or compel the interpofed bodies, into all spaces where it finds no greater refiftance than it can furmount; and fhew, that the er, exercised by nature, to avoid, or replenish a vacuum, is limited, and may be determined even to pounds and ounces *.

pow

And the experiment we are now upon, affords us a notable proof of the unheeded strength of the preffure fuftain'd by the free air, which we prefume to be uncomprefs'd: for hence we fee, that even in our climate, and without any other compreffion than what is natural, or ordinary, it bears fo strongly upon contiguous bodies, that a cylinder of it, not exceeding three inches in diameter, is able to raise, and carry up a weight, amounting to between fixteen and feventeen hundred ounces. In more nor¬ thern countries, the air may be much thicker, and able to fupport a greater weight; fince the Hollanders, who were forced to winter in Nova Zembla, found the air there fo condens'd, that they could not make their clock go, by a very great addition to the weights that used to move it.

Specific gra

vacuo.

34. We took a dry bladder, ftrongly ty'd at the neck, and about half filled with air, and faftening it to one part of a very exact balance, we put a metalline counterpoife into the oppofite fcale; and fo the two weights being brought to an equilibrium, the balance was convey'd into the recei- Bodies of diffever, and fufpended from the cover of it: when we obferv'd, that presently went fir after laying on the cover, the bladder appear'd to preponderate; where-equilibrium in upon the fcales being taken out, and reduced very near to an equilibrium, yet fo, that a little advantage remain'd on that fide to which the metalline weight belong'd; they were again let down into the receiver, which was prefently clofed. Soon after this, before the pump was work'd, the bladder feem'd again a little to preponderate; and the air in the glass beginning to be drawn out, the bladder expanded itself, and greatly raifed the oppofite weight, by drawing down the fcale to which it was faften'd, efpecially when the air had fwell'd it to its full extent. This done, we very leifurely let in the external air, and obferv'd that, upon the flagging of the bladder, the fcale whereto it was faften'd, not only, by degrees, return'd to an equilibrium with the other; but, at length, was a little outweigh'd by it; tho the bladder, after a while, began again to preponderate, and, by degrees, to fink lower for feveral hours: wherefore, leaving the veffel closed up all night, we, next morning, found the bladder fallen "All the parts of space," fays Sir Ifaac Newton," are not equally full; for if they were, the specific gravity of the fluid, "which would fill the region of the air, "could not, by reafon of the exceeding great denfity of its matter, give way to "the fpecific gravity of quick-filver, gold, or any body how dense foever; whence

66

ne ther gold, nor any other body, could "defcend in the air. For no bodies can "defcend in a fluid, unless they be

A

"fpecifically heavier than it. But, if a

quantity of matter may, by rarifa"aian, be diminish'd in a given space, "why may it not diminish in infinitum? "If all the folid particles of bodies,

are of the fame denfity, that is, have "their vires inertia as their magnitudes, "and cannot be rarified, without leaving pores, there must be a vacuum". Newton. Princip. p. 368.

yer

PNEUMATIC yet lower: as if the very fubftance of it, had imbibed fome of the moisture wherewith the air then abounded; as the ftrings of mufical inftruments, are known to fwell fo much in rainy weather, as to break. This conjecture is the more to be regarded, because having a little warm'd the bladder, we found it lighter than the oppofite weight. And, without removing the fcales, or the cover of the receiver, we again caus'd the air to be drawn out; the weather continuing very moift; but found not any manifeft alteration in the balance.

The afcent of liquors in fiphons, and fil

tres, whence.

Fig. 58.

...

But to make the experiment with a body, lefs apt to be alter'd by the temperature of the air, than a bladder, we brought the fcales again to an equilibrium with two weights, the one lead, and the other cork. And, having exhaufted the receiver, obferv'd, that both upon the exfuction, and after the return of the air, the cork manifeftly preponderated: and much more, a while after the air had been let in again, than whilft it was kept out. Wherefore, for the cork, we fubftituted a piece of charcoal, as lef's likely to imbibe any moisture from the air; but the event proved much the fame; fo that this experiment feems very liable to cafualties.

35. The true cause of the ascent of liquors, in fiphons and filtres, remaining unknown; we were defirous to try whether the preffure of the air might reasonably be fuppofed to have any confiderable share in it. But, because we could not fo far evacuate our receiver, but the remaining air would impel the water to a greater height than is ufual in filtrations; instead of a lift of cotton, or the like filtre, we made ufe of a fiphon of glafs, confifting of three pieces, two ftrait, and the third crooked, to join them together; whofe junctures were carefully clofed, that no air might find entrance at them: one of the legs of this fiphon was fomewhat longer than the other, and pervious at the bottom of it, only by a hole almoft as flender as a hair, that the water might drop very gently out of it. The shorter leg of the fiphon was quite open at the end, and of the fame diameter with the reft of the pipe; that is, about a fourth of an inch. The whole fiphon was defign'd to be about a foot and a half long, that the remaining air, when the veffel was exhaufted, might not impel the water to the top of it: then the fiphon, being inverted, was fill'd with water, and the fhorter leg let down, two or three inches, into a glafs-veffel; whilft the upper part remain'd faften'd to the infide of the cover of the receiver.

And, till a confiderable quantity of the air had been evacuated, the water dropp'd freely out at the lower end of the lower leg of the fiphon; as if the experiment had been made in the free air: but, afterwards, the bubbles began to appear in the water; and, afcending to the top of the fiphon, run into one, which was gradually augmented by the rifing of other bubbles, that, from time to time, broke into it, but much more by its own dilatation, which increased, proportionably, as the receiver was evacuated fo that, at length, the water, in the fhorter leg, was reduced, by 'the extraction of the ambient air, and the expanfion of the great bubble, at the upper part of the fiphon, to the height only of a foot; whence, the

courfe

courfe of the water, in the fiphon, was interrupted, and that which re- PREUMATICE main'd in the longer leg of it, continued fufpended there, without dropping any longer. But, upon turning the ftop-cock, the external air got into the fiphon, by the little hole at which the water formerly dropp'd out: and, traverfing all the incumbent cylinder of water, in the form of bubbles, join'd itself with that air which before poffeffed the top of the fiphon.

To prevent the inconveniences arifing from these bubbles, two glafspipes, like the former, were fo placed, as to terminate together in the midst Fig. 39. of the belly of a glafs-vial, into whofe neck they were cemented; and then both the vial, and the pipes, being filled with water, the fiphon was placed with its fhorter leg in the glafs of water, as before; and the experiment being profecuted after the fame manner, much more air was now drawn out before the bubbles caused any disturbance; because there was room enough in the vial for them to ftretch, without depreffing the water below the ends of the pipes; and during this time, the water continued to drop out of the lower leg of the fiphon. But, at length, the receiver being very much emptied, the water ceafed to run thro' the fiphon; the upper ends of the pipes beginning to appear above the remaining water in the vial, the dilated air wherein, feem'd likewife to prefs down the water in the pipes, and fill the upper part of them.

Hence, the experiment being interrupted, we let in the air again, which, according to its various proportions of preffure, to that of the air in the vial, and the pipes, exhibited a pleafing variety of phenomena. And upon the whole, there feem'd little caufe to doubt, if the bubbles had not disturb'd the experiment, that the courfe of water, thro' fiphons, would have appear'd to depend upon the preffure of the air.

An eminent mathematician lately told me, fome French gentlemen had Their afcent in obferv'd, that, if one end of a flender open pipe of glafs, be dipp'd in wacapillary tubes ter, the liquor will afcend to fome height in the pipe, tho' held perpendicular to the plain of the water; and, foon after, brought me two or three fmall pipes of glass, which gave me the opportunity of trying it: tho' I had often before, in the long and flender tubes of fome weather-glaffes, made after a peculiar manner, taken notice of the like afcent of liquors; but, prefuming it to be cafual, I made little reflection upon it. But, after this trial, fuppofing that tho' the water, in these pipes, rofe not above a quarter of an inch; yet, if the tubes were flender enough, it might afcend to a much greater height; I caufed feveral of them to be dextrously drawn at the flame of a lamp, in one of which, that was almoft incredibly flender, we found, the water afcended five inches, tho' the pipe were. held erect: but, if it were inclined, the water would fill a greater part thereof. We alfo found, that, when the infide of the pipe was wetted before-hand, the water would rife much better than otherwife. And fome of these flender pipes, being bent, like fiphons, we immers'd the fhorter leg of one in a glafs of fair water; and found, that the water, rifing to the top of the fiphon, of itself, ran down the longer leg, and continued.

run