PNEUMATICS cles of the diffolved gum, which, after a while fubfiding, leave the liquor tranfparent, themselves only remaining white. But, in our cafe, 'tis from the varied texture of the whole tranfparent fluid; and not from any particular part, that this whiteness results: for the body is white throughout, and will long continue fo; and yet may, in procefs of time, without any addition, be totally reduced into a tranfparent body, as before. Another conjecture, we grounded upon this obfervation: having convey'd fome fmoke into our receiver, placed againft a window, we obferv'd, that, upon the exfuction of the air, the corpufcles floating in it, manifeftly enough made the receiver feem more opake, at the very inftant the air rufhed out. For, confidering that the whitenefs, whofe caufe we enquire after, did but fometimes appear, it feem'd not impoffible, that, at fuch times, the air in the receiver, might abound with particles capable of reflecting the light, in the manner requifite to exhibit a white colour, by being put into a certain unufual motion; as the new motion of their former fumes, made the infide of the receiver appear darker than before; and as our fmoking liquor, formerly mention'd, whofe parts, tho' they feem'd tranfparent, whilft they compos'd a fluid; yet when the fame corpufcles, upon unftopping the glafs, were put into a new motion, and difpos'd after a new manner, they render'd that part of the air opake, wherein they mov'd, and exhibited a greater whitenefs than fometimes appears in our receiver. But as to the reason why our phenomenon appears not conftantly, I remember not that we ever made the experiment in a fmall veffel, without finding the expeted whitenefs. But it remains to be explain'd, why in our great receiver, the phenomenon fhould fometimes be feen, and often not. All I have to fay on this head is, that the air about us, and much more that within the receiver, may be much alter'd by fuch cafes, as few are aware of. The learned Jofephus Acofta tells us, that " in America there are winds which naturally trouble the water of the fea, making it green and black, and others as clear as cryftal." And, tho' we convey'd into the receiver, the fcales and the pendulums, formerly mention'd, clear and bright; yet, after the veffel had been emptied, and the air let in again, the luftre of both appear'd tarnish'd by a beginning ruft. And, laftly, having, with pure fpirit of wine, drawn a tranfparent tincture out of a certain concrete, commonly reckon'd among minerals, we put it into a cryftal-vial, carefully ftop'd it, and lock'd it up in a prefs; and this liquor, being a chymical rarity, and of a pleafing golden colour, we had often occafion to view it; and took notice that once it feem'd to be very thick: whereupon, we imagin'd it poffible, that fome of the mineral corpufcles were then precipitating. But finding, after fome days, that tho' no precipitation had been made, and that the liquor,retaining its former vivid colour, was grown clear again, as before; we lock'd it up again in the fame prefs, and refoly'd to obferve whether the like changes would again appear in our tincture; and, in cafe they should, whether they might be afcribed to the alterations of the weather. But tho' during the greateft part of a winter, winter, and a spring, we obferv'd the liquor would often grow turbid, PNEUMATICE. and, after a while, clear again; yet we could not find, that it depended upon any manifeft changes in the air; which would be often dark and cloudy, when the tincture was clear and tranfparent; as, in clear weather, the liquor would, fometimes, appear troubled, and more opake. freeze in vacuo. 38. Into a glafs vial, open at the top, we put a mixture of fnow, and com- Water made to mon salt; and, in the midft of this mixture, fet a cylindrical glafs, closely' stopp'd at the lower-end, and open at the upper, where we fill'd it with common water; then let them all down into the receiver; and the pump being fet on work, the fnow began to melt fafter than we expected. However, by that time the receiver had been confiderably exhausted, which it was in lefs than a quarter of an hour, we perceiv'd the water, near the bottom of the glafs cylinder, to freeze; and the ice, by a little longer ftay, feem'd to increafe, and to rife fomewhat higher than the furrounding furface of the liquor whereinto, almoft all the fnow and falt were diffolved. The lafs being taken out, it appear'd that the ice was as thick as the infide of the veffel it fill'd; tho', into that, I could put my thumb. The upper furface of the ice was very concave, and, held against the light, appear'd not deftitute of bubbles; tho' they were fewer than if the water had been frozen in the open air. The like experiment we made, alfo, in one of our fmall receivers, with like fuccefs. But, whence proceeds that ftrange force, we may fometimes obferve in frozen water, to break the bodies that imprison it, tho' hard and folid? A ftone-cutter, lately complain'd to me, that, fometimes, thro' the negligence of his fervants, the rain being fuffer'd to foak into marble, the violent frofts coming on, would burft the ftones. And, another tradefman complain'd, that,even implements made of bell-metal, being carelessly expos'd to the wet, have been broken and fpoil'd by the water, which, having enter'd at the little cavities of the metal, was there, afterwards, froze, and expanded into ice. And Cabeus tells us, that he faw a huge veffel of exceeding hard marble split afunder, by congeal'd water. I know it will be faid, to folve this problem, that congelation doth not reduce water into lefs fpace, than it before poffefs'd, but, rather makes it take up more. But, tho' we grant, that water fwells in freezing; yet how cold, which, in weatherglaffes, manifeftly condenfeth air, fhould expand either the water or the intercepted air, fo forcibly as to perform what we have here related, remains to be discover'd. 39. We took an oval glafs, clear, and pretty ftrong, with a fhort neck 4 water-thermoat the obtufer end, thro' which we thruft, almoft to the bottom, a pipe of meter in vacuo. glafs, and closely cemented it to the neck: the upper part of the pipe was drawn, in fome parts, more flender than a crow's quill, that the changes of the air in the glafs-egg, might be the more confpicuous; then we convey'd into the glafs, five or fix fpoonfuls of water, part of which, by blowing air into the egg, was rais'd into the flender part of the pipe; fo that the water was interpos'd between the external air, and that included in the egg. This weather-glafs, was fo placed, and clos'd Fig. 45. Nnn 2 up PNEUMATICS. TICS up in the cavity of a fmall receiver, that only the flender part of the pipe, to the height of four or five inches, paffing thro' a hole in the cover, remain'd expos'd to the open air. Infects in vacuo. In evacuating the receiver, the water, in the pipe, defcended about a quarter of an inch; and this upon two or three repeated trials; which feem'd to argue, that there was no heat produced in the receiver, upon the exfuction of the air: for even a little heat would, probably, have been difcover'd by that weather-glafs; fince, by the bare application of my hand to the outfide of the receiver, the warmth, after fome time, having been propagated thro' both the glaffes, and the interval betwixt them, to the imprifon'd air, fo rarify'd it, that, by preffing upon the fubjacent water, it impell'd that in the pipe much higher than it had fallen downwards, upon the exfuction of the air. Yet we do not hence conclude, that in the cavity of the receiver the cold was greater after the extraction of the air, than before. If it be demanded, what then could cause the water to fubfide; we anfwer, that, probably, it was the ftretching of the glass-egg, which, upon the exfuction of the ambient air, was unable to refift, as formerly, the preffure of the included air, and of the atmosphere, which, by the intervention of the water, prefs'd upon its concave furface. This feems probable, as well from the experiment about breaking a glafs, by the force of the atmosphere, as because, when by drawing the air out of the receiver, the water, in the pipe, was fubfided, upon the re-admiffion of the external air, to prefs against the convex furface of the egg,the water was prefently re-impell'd to its former height: for, if a glafs-egg be blown exceeding thin, and afterwards broken, you may, by degrees, confiderably bend fome narrow parts of it; and upon the removal of what kept it bent, it will readily recover its former ftate. From our experiment, then, it appears either that there fucceeds no body in the room of the air drawn out of the receiver; or, that every fubftance is not fubtile enough, readily to pass the pores of glafs, tho' always fufficiently agitated to produce heat, wherever it is found in plenty. So that if we admit no vacuum, this experiment requires us to allow a great difparity, either as to bulk, or agitation, or both, betwixt fome parts of the atherial fubftance, and thofe which, here below, produce heat and fire. We try'd, alfo, what operation the extraction of the air would have upon camphire; which confifts of fuch volatile parts, that they will exhale without any greater agitation, than that of the open air. But we found not, that even this loofe body, was fenfibly alter'd thereby. 40. We convey'd a large flefh-fly into a fmall receiver; and, at another time, fhut into a great receiver, a humming-bee, that appear'd ftrong and lively; we alfo procur'd a white butter-fly, and inclos'd it in a small receiver; where, though at firft, he flutter'd about, yet, prefently, upon the exfuction of the air, he fell down, as in a fwoon; retaining no other motion, than fome little trembling of the wings. The fly, after fome exfuctions of the air, drop'd down from the fide of the glass, whereon fhe was was walking: but, that the experiment of the bee might be more in- PNEUMATICS. ftructive, we convey'd in with her a bundle of flowers, which remain'd fufpended by a ftring, near the upper-part of the receiver; and having provoked the bee, we excited her to fly up and down the veffel, till, at length, the lighted upon the flowers, when we prefently began to draw out the air, and obferv'd, that tho', for fome time, fhe feem'd to take no notice of it, yet, within a while after, fhe fell down from the flowers, without making any ufe of her wings. in the exhaufted 41. To fatisfy ourselves, in fome meafure, why refpiration is fo ne- Birds and mice ceflary to the animals, that nature hath furnifh'd with lungs, we took a receiver. lark, one of whofe wings had been broken by a fhot; but, notwithstanding this hurt, the bird was very lively; and put her into the receiver, wherein fhe, feveral times, fprung up to a confiderable height. The veffel being carefully closed, the pump was diligently ply'd, and the bird, for a while, appear'd lively enough; but, upon a greater exfuction of the air, fhe began manifeftly to droop, and appear fick; and, very foon after, was taken with as violent, and irregular convulfions, as are obferv'd in poultry, when their heads are wrung off, and died; (tho' when these convulfions appear'd, we let in the air,) with her breaft upward, her head downward, and her neck awry; and this within ten minutes, part of which time had been employ'd in cementing the cover to the receiver. Soon after we put a lively hen-fparrow, which was not at all hurt, into the receiver; and profecuting the experiment, as with the former, fhe appear'd to be dead within feven minutes; one of which was employ'd in. cementing on the cover: but, upon fuddenly turning the key, the fresh air, flowing in, began flowly to revive her; fo that, after fome pantings, the open'd her eyes, and regain'd her feet, and, in about a quarter of an hour after, attempted to escape at the top of the glafs, which had been unftop'd to let in the air upon her: but the receiver being clofed the fecond time, fhe died, violently convuls'd, within five minutes from the firft ftroke. of the pump. Then we put in a moufe, newly caught, and, whilft he was leaping up very high in the receiver, we faften'd the cover to it; expecting, that an animal, used to live with very little fresh air, would endure the want of it better than the birds; but tho', for a while after the pump was fet on work, he continu'd leaping up, as before; yet 'twas not long e'er he began to appear fick, giddy, and to ftagger; after which, he fell down as dead, but without fuch violent convulfions as the birds had when, haftily letting in fome fresh air upon him, he recover'd his fenfes, and his. feet, but feem'd to continue weak and fick; at length, growing able to skip, as formerly, the pump was ply'd again, for eight minutes; about the middle of which space, a very little air, by mifchance, got in at the ftop-cock; and, about two minutes after that, the moufe, feveral times, leap'd up lively; tho', in two minutes more, he fell down quite dead; yet with convulfions far milder than those wherewith the birds expired. This alacrity, fo little before his death, and his not dying fooner than PNEUMATICS than at the end of the eighth minute, feem'd owing to the air that pafs'd into the receiver: for, the first time, the convulfions feiz'd him, in fix minutes after the pump began to be work'd. Thefe experiments feem'd the more ftrange, becaufe, during a great part of those few minutes, the engine could but confiderably rarify the air, and that too by degrees; and, at the end thereof, there remain'd in the receiver, a large quantity: for, as we formerly faid, we could not draw down water in a tube, within much less than a fcot of the bottom. And, by the exfuction of the air, and interfperfed vacuities, there was left in the receiver, a fpace fome hundreds of times exceeding the magnitude of the animal, to receive the fuliginous fteams, from which, expiration discharges the lungs, and which, in the other cafes, may be fufpected, for want of room to stifle those animals that are clofely pent up in too narrow receptacles. The nature of refpiration confider'd. Having caufed thefe three creatures to be open'd, I could difcover little of what we fought for, and might, poffibly, have found in larger animals: for tho' the lungs of the birds appear'd very red, and, as it were, inAlamed; yet that colour is ufual in the lungs of fuch winged animals: but in almost all the deftructive experiments, made in our engine, the animals appear'd to die with violent convulfive motions. From whence, whether phyficians can deduce any thing towards the difcovery of the nature of convulfive diftempers, I leave to them to confider. And, to obviate objections, and remove fcruples, about the fuliginous fteams of pent up animals, which are fuppofed to kill them; we fhut up another mouse, as clofe as poffible, in the receiver, where it liv'd about three quarters of an hour; and might, probably, have done fo, much longer, had not a perfon of quality defired to fee whether the mouse could be kill'd by the exfuction of the ambient air. Upon this, we open'd, for a while, an intercourfe betwixt the air in the receiver, and that without, whereby the mouse might be refreshed, tho' without uncementing the cover at the top; to avoid the objection that, perhaps, the vessel was more clofely stopp'd for the exfuction of the air than before. The event was, that, after the moufe had liv'd ten minutes, the pump being a little out of order, he died with convulfive motions; wherein he made two or three bounds into the air, before he fell down dead. I, alfo, caufed a moufe, that was very hungry, to be fhut up all night into a well-clofed receiver, with a bed of paper for him to reft on; and caus'd the engine to be placed by the fire-fide, to keep him from being deftroy'd by the immoderate cold of a frofty night; and, the next morning, I found he had devour'd a large part of the cheese that had been put up with him. And, having thus kept him alive full twelve hours, we, by fucking out part of the air, brought him to droop, and to appear fwell'd; but, by letting it in again, we foon reduced him to his former livelinefs. It may be here expected, I fhould attempt to clear the nature of refpiration; but I pretend to go no farther in it, than our engine leads me. 'Tis alledged by those who would have the lungs rather paffive than active, in refpiration, that as the lungs, being deftitute of muscles and fibres, |