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THE Bulk of the former Volume, for∣bidding that I should add any more of the Experiments concerning the Air's Spring and Weight, I shall now proceed to lay down what our Author hath fur∣ther deliver'd in his first Continuation of Ex∣periments relating to that Subject.
AS in the Experiments recited in the for∣mer Volume, it appear'd, that the Pres∣sure of the External Air, occasions the Difficul∣ty of drawing up the Sucker of a Syringe; so I shall now shew, that the Pressure of the Exter∣nal Air, upon the Surface of the Water, in which the Syringe is immersed, causes it to as∣cend, when the Sucker is drawn up.
Having cemented a Glass Pipe to the lower End of a Syringe, and immersed the lower End of that Pipe in a Viol which contain'd Mercury, we tyed the Sucker of the Syringe to the Stopple which is in the Cover of the Receiver, and ha∣ving conveighed it into such a Receiver as Fig. 2. Plate 1. Represents;* 1.1 we observ'd, that upon drawing up the Sucker, the Mercury did not in the least ascend, till the Air was let into it, and then it ascended up to the Top of the Glass Tube: And this Experiment being varied, by drawing the Sucker up an Inch before the Recei∣ver was exhausted, the Mercury rose to the Top of the Glass Tube, tho' it did not in the least rise when the Sucker was drawn up as high a∣gain, after the Receiver was exhausted. And in trying this Experiment it was further to be noted, that when the Receiver was exhausted,
it was as difficult to raise the Sucker, as when the End of the Syringe was stopped, the remain∣ing Air which was able to keep the Sucker from rising, being unable to raise the Mercury.
The former Tryal being again repeated, be∣sides what we observed in that Experiment, we further noted, that a considerable Weight being tyed to the Syringe to keep it steady and firm, the Mercury did not rise till we permitted the Air to return again into the Receiver, tho' the Sucker was raised two Inches.
But lest the Phaenomena exhibited by these Ex∣periments, should be influenced by the Air con∣tain'd in the Glass Pipe; I caus'd the Pipe to be fill'd with Spirit of Wine, and immersed it in a Viol which contain'd the same Liquor tinged with Cocheneel; and observ'd, that tho', when the Re∣ceiver was exhausted, the Liquor afforded Bub∣bles plentifully, and at the Top seemed to boyl, yet it did not ascend in the least, notwithstand∣ing the Sucker was raised two Inches and a half: But when the Air was let into the Receiver a∣gain, it ascended into the Body of the Syringe, which appeared, by the small Quantity of Spi∣rit remaining in the Bottle, in which the Glass Tube was immersed.
HAving instead of the Glass Tube mention'd in the former Experiment, provided a crooked one of Brass,* 1.2 such as the first Figure represents, and joyn'd a Glass Tube to the short∣er Leg with Cement, we caus'd Weights to be fixed to the Top of the Sucker to depress it speedily when occasion required: This Syringe was fixed to a Pedestal to keep it firm, and to hinder it from tottering; and a Feather was likewise fixed with Cement to the lower End of the Syringe, so that the small End was placed above the Orifice of the crooked Tube. All which being conveyed into a Receiver, and the Pump set on Work, we observ'd, that, the Suck∣er by the help of the Turning-Key being of∣ten elevated and permitted to fall again, the Feather was gradually less shaken, with what was forced out of the Syringe, as the Receiver was more and more exhausted, till at the last the Feather did not seem in the least to be mo∣ved, before Air was again let in, and then it was blown up as before: In which Experiment we observ'd, that as the Cavity of the Receiver was more or less exhausted, the Descent of the Sucker was accordingly quickened, so that had there been a Substance finer than Air in the Re∣ceiver, the Blast would have been greater as the Descent of the Sucker was swifter.
We tryed the same Experiment a second time, contriving to draw up the Sucker higher than we did before, but the Event was no more sa∣tisfactory than the former.
But that I might be informed, what Quan∣tity of Air was drawn out every Exsuction, as well as when the Feather was more or less sha∣ken by the Wind thrown out of the Syringe, I made use of a Glass Tube, such as Figure the Third represents,* 1.3 instead of the former Brazen One; and the one End being immersed in a Jar, and placed in the Receiver, as the Air was pum∣ped out, several Bubbles broke through the Wa∣ter out of the Pipe, but External Air getting in at a Leak, the Water was pressed up into the Pipe again; nevertheless, upon an Exsuction of that Air it again subsided; yet yielded so ma∣ny Bubbles, that we could not conveniently make any further Observations, till the Recei∣ver having stood still for some time, the Water was freed from Air; and then, tho' the Pump was set on Work, till the Gage discovered the Receiver to be very well exhausted; yet we could not discern, that any Bubbles were forced through the Water in the Bottom of the Tube by fre∣quently elevating and depressing the Sucker; for tho' there appear'd a few in the Top of the Water, yet we judged that those rather pro∣ceeded from some aery Particles lodging in the Pores of the Water.
But what was most Remarkable in this Expe∣riment was, that after some time the Water ri∣sing about an Inch in the Tube, above the Sur∣face of the Water without it, we several times rais'd the Sucker 2 or 3 Inches, and fuffered it
to fall again, without perceiving, that the Wa∣ter in the Tube was in the least Affected; which is an Argument either of a Vacuum, or that the Parts of that Aether are so fine, that they exceed the Rarefaction of the Air so far, as not to be able to effect what a Particle of Air does which is not above 1/500 part of the Quan∣tity of a Pin's head; a Particle of Air, before Expansion, of that Minuteness being able, when the Receiver is exhausted, to displace much more Water upon their Expansion than this Ae∣ther.
By which Experiment, as well as what we have taken notice of, the Reason I formerly as∣sign'd for the rising of Water in Syphons seems to be confirm'd; the Water in the Pipe made use of in these Experiments, not being able to rise when the Air was exhausted, tho' the Suck∣er was drawn up, till Air was permitted to en∣ter into the Receiver again.
TO discover whether so light Bodies as Fea∣thers would be affected in their descent in the exhausted Receiver by any subtle Matter contain'd in it, we fix'd a small pair of Tobac∣co-Tongs in such a Receiver as Fig. the Fourth Represents,* 1.4 which was 22 Inches high, and ha∣ving joyn'd four Feathers together with Cement,
so as to lie across each other, we fixed a small piece of Paper to them, which being held in the Tongs, the Feathers hung in an horizontal Po∣sture; And upon an Exsuction of the Air out of the Receiver, till by a Mercurial Gage it seem'd void of Air, we open'd the Tongs, by turning the Stopple in the Cover of the Receiver, (a short String, the one End of which was fixed to the Stopple, and the other to the Tongs, being by that means shortned) upon which we ob∣serv'd, that tho' these Feathers turned several times in the unexhausted Receiver, yet the Ex∣periment being often repeated, we could not per∣ceive them in the least to turn in the exhausted Receiver, but to fall like a dead Weight; and what was further to be observed was, that the Descent of the Feathers was much quicker in the exhausted Receiver, than when it was full of Air.
Yet in this Experiment it was observed, that the Phaenomena were less convincing than the for∣mer, because we took notice that the Feathers fell without in the least turning when the Re∣ceiver was but half exhausted.
And we further noted in this Experiment, that, the Receiver being lengthened with a Cy∣linder of Laton, cover'd over with Cement, and kept from being press'd too much inward by the outward Air, by a Case made of Iron Bars, when the Air was let in again into the exhaust∣ed Receiver, it made a considerable crackling Noise, the sides of the Metalline Receiver which before were in some measure compress'd being again extended.
HAVING caused a Cylinder of Box to be turned,* 1.5 with an Axle-tree at each End, into the Cavity of the uppermost was received the Bottom of the Stopple; and the Axle-tree at the Bottom was adapted to a Hoop of Brass fixed in the middle of a Trencher, which was about 5 Inches broad, and 3 thick, and which had a piece of Lead fixed to the Bottom to keep it steady; which being done, a Wyer was fixed in the upper part of the Trencher, and at the End, which bent downwards, was fixed a Bell, and at another place of the same Trencher was fixed a Steel Spring, to the upper part of which a piece of Steel was joyn'd, at such a convenient Distance, that when it was bent back by two Pegs placed at right Angles in the Cylinder (which had several Holes made in it on purpose) and the Spring on a sudden ceased to be pressed up∣on, it would fly forcibly upon the Bell, and give it a smart Stroak.
Things being thus ordered, I caused the Re∣ceiver to be exhausted, and tho' the Sound (which was caus'd by turning the Cylinder fixed to the Stop-Cock, so as to make the piece of Steel strike upon the Bell) was scarce discerni∣ble, yet as Air was gradually let in, it became louder and more audible.
And the like Experiment being tryed by sus∣pending a Watch which had an Alarum belong∣ing to it, by a piece of Thred, which was ty∣ed to a Glass Button purposely blown in the in∣side of a Receiver which was made of one en∣tire piece, so that it was less subject to break; we ordered the Watch so, that the Alarum should begin to go by the time that we were ready to make our Observations, at which time one that held his Ear near enough to the Top of the Receiver, perceiv'd, that when the Air was wholly exhausted, the Sound of the Alarum was scarce at all discernible, but became much louder as the Air was gradually let in.
TO know the Reason, why upon the Break∣ing of a Part of the solid Case of the Stem of a Glass Drop, which upon it's first Formation falling into Water, was kept full of Rarifi'd Air; I say, to know the Reason, why such a Bottle flies in pieces when part of the Stem is broken off upon a sudden Ingress of External Air; I caused the lower End of a Glass Drop to be fastened to a staple Body, the Stem being tyed to one End of a String, and the other End being fastened to the Turn-Key; which being done, and the Receiver exhausted, the Stem was broke off by short∣ning the String, whereupon the Bubble flew
into a Thousand Pieces, the Air inclosed ex∣panding violently, and endeavouring to rush out at that small Vent.
TO try whether Light might be produced in the Exhausted Receiver without an Access of Air, we made use of a Virtical Cylin∣der, the lower Basis of which was fixed in a Staple Trencher; and having fixed two pieces of Steel in the lower End of that Cylinder, so as to rub forcibly against a Lump of Loaf-Sugar, I observ'd, that the Vitriol Cylinder being forcibly turn'd by the help of the Turning Key, the Steel made Impressions strong enough upon the Sugar, to cause it to afford, not on∣ly several Flashes, but little Sparks of fire.
WE made use of a large inverted Cucurbite for a Receiver, which being exhausted, and a large Candle held on the Opposite side, when the Stop-cock was turned, to give way for the Air, to pass out of the Receiver into the Cylin∣der, the Cavity of the Cylinder seemed to be filled with Fumes; so that the Candle whose Flame was visible, though it appeared to be en∣compassed
with a kind of Halo, whose Colour was between Blew and Green; and after a few Exsuctions, would be of a Reddish or Orange Colour, very vivid: Which Meteor I supposed to arise, from some Particles of the Turpentine, which extricating themselves upon the Applica∣tion of a hot Iron to the Cement, caused an Explo∣sion in the Receiver, when the Parts of the Air were put in Motion and disposed to Expansion; and the variety of Colours, I conceive to pro∣ceed from the various Positions of those Particles of Matter which fill up the Receiver and vari∣ously reflect the Rays of Light. To confirm which Opinion I observed several Steams to rise up from the Cement upon turning of the Stop-cock; and if we continued to exhaust the Re∣ceiver, it would become clearer and clearer, and the Colours more dilute, till the Cement was enabled to emit more Steams, by re-ap∣plying a hot Iron to it: And as for the Reason, why these Steams do not so plentifully rise, when the Receiver is evacuated, it appears to be, because the Particles of the Turpentine are less agitated as the Heat declines; and further, be∣cause they want Air to support them.
To confirm what I have intimated, as the Causes of the aforementioned Phaenomena, I con∣veyed some of the Cement Melted in a Crucible into a Receiver; and observed, that upon open∣ing of the Stop-cock to let out the Air, the Steams would for some time plentifully fly about, but after a little time would subside again. But in the aforementioned Phaenomena, the several Colours seemed to depend on the different De∣grees of Heat which the Cement acquired; as
also, on the different Size and Figure of the Re∣ceiver; as also, on the Nature of the Cement and the Quantity of Air which was left unpum∣ped out.
HAving conveyed an Evaporating Glass, with a sufficient Quantity of Water in it into the Receiver, when the Air was drawn out, we let down a piece of unslacked Lime into it, by the Assistance of the Turning-Key; and ob∣serv'd, that in about ¼ part of an Hour, the Lime began to slack violently, and at each Ex∣suction afforded very large Bubbles, which con∣tinued as long as we plyed the Pump; so that in a little time the whole inside of the Receiver was cover'd over with Lime Water, a great part of the Mixture boiling over into the Capacity of the Receiver; in which Experiment the Outside of the Vessel was considerably hot, and the Mixture continued its Heat near ¼ part of an Hour after the Receiver was removed: The Lime made use of in this Experiment was very strong.
TO measure the force of the Air's Expansi∣on, we fixed a Syringe in a Frame, that it might be kept firm and erect; which being done, we provided a Leaden Hoop, which was sus∣pended at the Top of the Sucker, and hung so far below the Bottom of the Syringe, that it might have Space enough to rise in upon the Ex∣pansion of the Air in the Cavity of the Syringe, when the Receiver should be exhausted; the Weight in the mean time being prevented from compressing the Air beyond it's natural State by a String, the one end of which was tyed to the Top of the Sucker, and the other to the Turn∣ing Key; which being done, and the Pump set on Work, we found, that the Expanding Air was able to raise about 7 or 8 pound Weight, and had the Rammer had a free Passage it probably would have raised a much greater Weight; but the Experiment was less satisfactory in determin∣ing the force of the Air's Expansion, in elevating a determinate Weight; because the Air made it's way too easily betwixt the convex Superficies of the Sucker, and the concave Surface of the Cylinder.
Therefore to be more exact, I caused two Cy∣linders to be made different both in Length and Breadth, the Diameter of the one being an Inch,
and of the other two Inches; In the former, I put a Lamb's Bladder, which contained a suffici∣ent Quantity of Air, and having ordered the Receiver to be exhausted, I found, that a Cylin∣der of Air of an Inch Diameter, was able to raise a Weight of 10 Pound Averdupoiz Weights; but tho' the Bladder for a long time kept the Air from flying away, yet when it was loaded with the utmost Weight it was able to bear, some Air getting out of the Bladder rendred our Tryal less satisfactory.
Wherefore we made use of a Cylinder 4 Inches Deep and two in Diameter, which having a broad Basis to stand upon, we put a Lamb's Blad∣der into it well blown and tyed;* 1.6 and putting a Wooden Plug upon that, we loaded the Plugs with Weights amounting to 35 Pound, the up∣permost of which was fastned to the Turning-Key, to prevent it from falling, and then the Plug being marked at the brim of the Cylinder, we set the Pump on Work, and observed that the Expansive force of the Air in the Bladder was so great that it lifted up the Plug consider∣ably; yet when the Air was again let into the Receiver the Plug was so far depressed that the Mark was below the Edges of the Receiver; yet the Air being again a second time exhausted, the Bladder raised the Plug so high, that ⅜ parts of the whole Plug was lifted up above the Edges of the Cylinder. And by repeating the Tryal we found, that the Air in the Bladder, when the Receiver was exhausted, was able to bear up 7 pound Weight more, by which Weight the Mark upon the Plug, was not depressed below the top of the Cylinder.
But in trying these Experiments the follow∣ing Particulars are to be Noted.
1. That the Plug must be so adapted to the Cy∣linder as to move up and down easily; also it must be of a convenient length, not exceeding an Inch and a half; and it will be likewise re∣quisite that the Plug should have a strong Ledge upon the upper part of the Cylindrical Surface, that it may rest upon the Edges of the Cylinder and sustain the Weights laid upon it more firm∣ly.
2. When the Bladder was put into the hollow Cylinder, we took care to adapt it by easie and frequent Compressions to the Cavity it was pla∣ced in, making a Mark in the inside of the Cylinder where the Air in it's Natural State was Compressed to, that we might learn what Weight the Expansion of the Air was able to sus∣tain above that Mark; for the Air being preter∣naturally compressed, upon the Account of that accidental pressure may be able to raise a greater Weight than Air uncompressed, so that the Weight it raises above that Mark is alone to be taken for what Air condensed is able to lift up more than the Air in it's Natural State.
3. When the Bladder was taken out of the Cylinder, the Figure of it was proportionable to the Cavity, which it was contained in, being 2 Inches Diameter, and 2 Inches and ½ long.
4. From the Experiments now mentioned it appears, that the Air is able at it's first Expansion, to raise a Weight proportionably larger accor∣ding to the different Bores of the Cylinders
made use of; but when it hath been a little more Expanded the Proportion is not so exact, be∣cause a small Quantity of Air being to fill up ¼ or ½ part of an Inch more, the smaller Quantity of Air must be much more rarified and conse∣quently lose of it's expansive Force.
But comparing the expansive Force of Air in different Bores at it's first Expansion, some may think the Proportion not exact; since the small Bladder being able to raise no more but 10 Pound, and the Weight which the larger raises being 42, it is more than a Duplicate Proportion-of what our Hypothesis requires; but if we consider that comparing the Diameter of each Cylinder, the Bladder in the less, proportion ably takes up more Room than in the larger; it may be sufficient to account for the Differ∣ence.
5. Considering that the Bladders in which Air is Included, may straiten the Cavities of the Cylinders, the expansive Force of the Air might be more exactly determined, could Cylinders be contrived stanch enough without such helps.
6. And it will not a little contribute to ren∣der the Force of the Air's Spring difficult to be determined, that the Air it self at different times varies, in it's degrees of Pressure: Yet from what hath been said it seems probable, that were it possible to contrive an exact Cy∣linder very tite one, of an Inch Bore would be able to raise above 10 pound Weight.
TO demonstrate more obviously the Air's Spring, we took a* 1.7 Brass Cylinder whose Depth was 4 Inches and it's Diameter 4 Inches and ¾, to which we adapted a† 1.8 short Plug, to whose upper Basis was fixed a broad Rim for Weights to stand on more firmly; which being done we pressed a Bladder into the Cylinder, that it might adapt it self to the Cavity of it; and then, observing, how much the Plug was above the surface of the Cylinder, we laid the Weights upon it (see Plate the 2d Figure the 5th) and observed that the Air in a Cylinder about 4 Inches broad lifted up 75 pound at the 5 Exsuction so high that one might discern the Mark;* 1.9 and at 2 Exsuctions more it was elevated 3/10 above the Top of the Cylinder, and at the same time, in a Mercurial Gage the Mercury that usually stood at ⅛ above the highest Glass Mark subsided to ⅛ below the Second. When the Air was let into the Receiver again, after some time the Bladder subsided again, and being taken out exactly answered the Cavity of the Cylinder. The Receiver being again exhausted at the 24th Exsuction the Mercury in the Gage was de∣pressed to the lowest Mark, and at the 35th to ⅛ below it.
And the former Experiment being tryed in a small Receiver in which we heaped flat Weights one upon another, the Air raised 100 pound
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Weight, and would probably have raised much more, had it not been, that the Bladder was so much strained as to give way for some Air to get out at a Leak.
And here it may not be improper to advertise, that the Orifices of such Receivers must not be very wide, for if they be they will be subject to be crack'd by the violent external Pressure of the Atmosphere.
TO Compare the Gravity of Air and Wa∣ter, I weighed a Glass Bubble in the Re∣ceiver, which I found to weigh above half a Grain more in the exhausted Receiver than be∣fore the Air was drawn out; and this Bubble being weighed in the open Air counterpoised 68 Grains and an half; upon which the Bubble being immersed in Water, we found that the Air in it had been so far rarified by the Heat employed in sealing it up, that the Nip being broke off, it sucked in 125 Grains of Water, the Glass together with the Water sucked into it weighing 193 ½ Grains: The whole Cavity of the Bubble being large enough to contain 739 Grains of Water, it weighing 807 ½ Grains, so that the Proportion betwixt the Weight of the Air and Water did not quite amount to 1228 to 1.
Having weighed a Glass Bubble in the Recei∣ver, whose Weight was 60 Grains, the Air con∣tained in it in Vacuo weighed 27/92 of a Grain, and the Weight of such a Quantity of Water as it would contain, weighed 720 ¼ Grains. In
which Experiment the Proportion of Air to Water in Weight was as 857 17/27 to one. But Galileo says, Water is but 400 times heavier than Water, tho' Ricciolus is as much mistaken on the other side, who says it is 10000 times hea∣vier.
To inform my self further of the Weight of the Air, I took the following Measures; having exhausted a Receiver, and when it was void of Air counterballanced it, upon turning the Stop-Cock and a Reingress of Air, it weighed 36 Grains more than before, which succeeded when tryed a second time, and likewise a third. And then the Receiver being exhausted was immersed in Water, and the Stop-Cock turn'd to give way to an Ingress of Water, and when as much Water as was able to enter into the Receiver had succeeded in the Place of the exhausted Air, we turned the Cock again to keep that Water in, and the Receiver being again weighed, the Water weighed 47 Ounces, 3 Drachms and 6 Grains, so that the Water was heavier than its bulk of Air, near 650 Grains, the Mercury in a Baroscope at the same time being boyed up to 29 Inches ¾, so that the Weight and condensed state of the Atmosphere being greater then than usually, was the Reason why the Disproportion was not as great as at other times; tho' we may reasonably suspect, that the Quantity of Air contained in the Pores of the Water, joyning with that in the Receiver, might hinder so much Water from getting in as was requisite to fill the Space deserted by the Exhausted Air; besides several Particles of Air might probably get in at the Stop-Cock, whilst the Experiment was
trying, which joyning with the Air remain∣ing in the Receiver might contribute to prevent a sufficient Ingress of Water.
From all which Experiments it appears, that tho' the Weight of the Atmosphere is so vari∣ous, that it is impossible to know exactly the Proportion betwixt it and Water, yet it is e∣vident that Water is to Air some Number be∣twixt 600 and 1100 to 1, being greater or less as the Atmosphere is more or less conden∣sed. But these Tryals are only of use in Eng∣land, for the Weight of Water as well as Air, is so different in most Countries, that it is requisite to make frequent Experiments in each, to determine the Proportion of the Weight of Air in such Places.
See Plate 1. Fig. 2.
See Plate 1. Fig. 1.
See Plate 1. Fig. 3.
See Plate 1. Fig. 4.
See Plate 2. Fig. 1.
See Plate 2. Fig. the 2 and 4.
See Plate the second Fig. 4.
See Plate
See Plate 2. Fig. 5.