The works of the Honourable Robert Boyle, Esq., epitomiz'd by Richard Boulton ... ; illustrated with copper plates.

CHAP. IV. Concerning the cause of the Condensation of the Air, and ascent of Water by Cold in common Weather-glasses.

COncerning the Reason, why Water in com∣mon Weather-glasses descends upon Heat, and is raised by Cold? there are three Opinions which may deserve our Consideration.

* 1.1The first is, that of the Schools and com∣mon Peripateticks, which teaches, That the external Air condensing that included in com∣mon Weather-glasses; it rises to fill up that space deserted by the Air to prevent a Vacuum. But not to urge, That they have not yet pro∣ved, that Nature will not admit of a Vacuum, or that it is contrary to the Notion a Naturalist ought to have of Matter; to suppose it to act any thing contrary to its own natural tendency for a publick Good: I say not to urge these Argu∣ments, which we have elsewhere made use of; I shall alledge the following Experiment. viz. That,

* 1.2If a Bolt-head with a long Stem be made use of to try the Torrecellian Experiment with, the space deserted by the Mercury in the Cavity of the Bolt-head, and from whence the Mercury drove the Air, continues void; the Pendulous Cylinder remaining at 30 Inches, without offer∣ing to ascend to prevent a Vacuum. Nor will the Quick-silver rise ¼ of an Inch higher upon the application of cold Bodies outwardly; tho' in a common Thermometer, the same degree of Cold would make Water ascend several Inches.

To this I shall add another Argument taken from the consideration of sealed Weather-glasses (see Plate 1. Fig. 3.) in which it is observed,* 1.3 That the Air, instead of contracting upon an in∣crease of Cold, expands it self. If it be said, That the Water contracting the Air follows it to prevent a Vacuum; it may be demanded, Why, since Nature causes the one to contract in com∣mon Glasses, and the other in sealed ones, to a∣void a Vacuum; she does not rather make the Air retain its natural extension than suffer it to be condensed, and then put her self to double trouble, in compelling the Water to as∣cend contrary to its nature?

But not to insist on these Arguments, I shall rather urge, that what is offered by them will not solve the Difficulty; for whether the Water or Air be expanded into a large space, since Glass is impervious to Air and Water; I see not how a Vacuum interspersum and coacervatum can be avoided: For if upon the expansion, no o∣ther Body is added and penetrates the Glass to fill the space deserted by some Parts of the ex∣panded Body, there must remain Vacuities be∣twixt them: Because it is impossible, the same quantity of Matter should compleatly and ade∣quately fill a greater space by being expanded; the Parts of the Body being only able inade∣quately to fill it by receding from each other: But were it allowed, that upon the expansion of one of these Bodies, and the condensation of the other, a third Substance harboured in the space deserted by the one; it may be questioned, how such Matter should make its way out again?

* 1.4The second Opinion I shall take notice of, is that of Mr. Hobbes, which is to me partly pre∣carious, partly insufficient, and scarce intelligi∣ble; for tho' when he asserts, That the coldness of Liquors depends on their being pressed with a constant Wind, besides that he asserts it without Proof; it will appear from an Experiment short∣ly to be alledged, That Liquors sealed up in Glasses, and suspended in Liquors not subject to freeze, may be refrigerated; tho' it appears not how they can be raked on by the Wind as his Hypothesis requires.

Secondly, I see no necessity, that the Cold should press upon the superficies of the Water in the Shank; since by Cold it will be raised in a Weather-glassess, kept in a still Place and void of any sensible Wind. Besides, he ought to shew, Why Air insensibly moved deserves to be styled Wind, and how it is possible such a Wind should raise Water so many Inches by pressing upon it? Nay further, Water poured into a Bolt-head till it reaches into the Stem, will subside when refrigerated, and not rise. And if the Ball of a Weather-glass be encompassed with a mixture of Ice, or Snow and Salt; the Water will readily ascend; which how it will be explained by Mr. Hobbes's Hypothesis, I do not see.

Thirdly, Mr. Hobbes allowing not of a Vacuum, I wonder he should tell us, That by a bare Pres∣sure, the Water finding no other Place to re∣cede into, is forced to rise into the shank of the Weather-glass: For since, according to him, the shank of the Weather-glass must be full be∣fore; I see not how it should be able to receive the ascending Water, except to use Mr. Hobbes's

own words, it can be fuller than full. Besides, it may be further alledged against Mr Hobbes his Doctrine, that it gives us no account of the con∣densation of the Air by Cold, in Weather-glas∣ses in which the Water descends with Cold and rises with Heat.

Fourthly, whereas Mr. Hobbes in explaining the depression of Water in Weather-glasses, at∣tributes it solely to it's own Gravity; it will easily appear, that we must likewise have re∣course to the spring of the included Air: For if a Thermometer be placed in the Sun, when the Water in the shank is but a little above the Sur∣face of the Water without the Tube; the rari∣fied Air will depress the Surface of the Water in the Pipe below the other, and sometimes so far, that some of the rarified Air making it's way out of the Pipe, as soon as the remaining Air is refrigerated again, the Water will be able to rise up higher into the Tube than it did be∣fore.

* 1.5The third and last Opinion I shall consider is one held by some modern Naturalists, which ascribes the Ascent of the Water to the Pressure of the Air gravitating upon the Surface of that Water without the Pipe; but supposes that the Air contained in it, is contracted by Cold a∣lone: As for the first Part of this Hypothesis, I readily Assent to it;* 1.6 but am apt to believe that the contraction of the included Air depends on the same Cause, and that the spring of it being weakened by Cold, it is condensed by the same Pressure of the Atmosphere; the weight of the External Air over-powering the weakened Spring of the Internal.

In favour of this Opinion I shall add the fol∣lowing Experiments,* 1.7 and First, having filled a Vial capable of holding five or six Ounces, half full (See Plate 1. Fig. 5.) and having inverted a Glass Tube into it, about 10 Inches long, much bigger than a Swan's Quill, it being first sealed at one end and filled with Water; the Orifice of the Vial was closed with Cement, so that the External and Internal Air, had no communication with each other: It was placed in a Mixture of Snow and Salt, till the Water in the Bottom of the Vial began to freeze; yet notwithstanding so great a degree of refrigera∣tion, the Water in the Tube did not at all de∣scend; so that either the Air was not conden∣sed by Cold, or the Water descended not to prevent a Vacuum. The Glass being left in this Posture, in our absence, the sealed end of the Pipe flew off; being beaten out by the In∣tumescence of the freezing Water.

Having fixed another Pipe as the former, which was some Inches longer, and drawn ve∣ry slender at the sealed end, that it might easi∣ly be broken; this was set to freeze as the o∣ther, yet the Water descended not, but as soon as the top of the Glass-Tube was broke off, the external Air pressing upon the Water, and by the intercourse of that upon the Air; the Water in the Tube subsided 8 or 10 Inches, but rose again when the internal Air was rari∣fied, within half an Inch of the top; and then the Apex being sealed up it was placed in Snow and Salt, yet the Air in the top, had it's Spring so weakened by refrigeration, that it was not able to depress the Water; tho' as soon as the

Apex was broke off, it subsided several Inches, the external Air pressing upon it.

The Experiment being a third time reitera∣ted with 3 ½ of Air in the Pipe, when the Wa∣ter in the Vial was in some measure froze, it was able to expand it self a little: But when the Apex was broke off, the External Air de∣pressed the Surface of the Water two Inches, but being removed into a warm Room it as∣cended above an Inch higher than the upper∣most Level.

Having put so much Water into a Vessel,* 1.8 (Such as Plate 1. Fig. 6. Delineates) as was a∣ble to fill almost the whole Tube, we caused a Mixture of Snow and Salt to be placed about the Ball of it, yet we perceived not the Wa∣ter in the least to rise; but if at all, it might well be ascribed to the the Intumescence of some airy Parts lodged in the Pores of the Water. But the Apex of the Tube being broke off under Water, the External Air forced the Water several Inches up into the Cavity of the Pipe.

Another Experiment we made with the fol∣lowing Vessel (See Plate 1. Fig. 7) the Stem of this being no thicker than a Raven's Quill tho' several Inches long,* 1.9 and the Ball being about as big as a Nutmeg; we dropped a few drops of Water into the Stem which being suspended there, betrayed very slight changes in the Rare∣faction or Condensation of the internal Air. Watching therefore when the Air within had raised the Bubble up to the top of the Stem; we immediately sealed it up, and observed, That tho' the sealed Glass was placed in a Mixture of

Snow and Salt, the Bubble did not in the least subside: But if the Apex of the Stem was broke off, the Bubble of Water would be sometimes depressed so low, as to fall into the Ball of the Weather-glass. And what was further remark∣able, was, That when the Liquor was descending, if the end of the Tube was sealed up; the Wa∣ter would immediately stop at the place it rest∣ed at, when the Pressure of the Atmosphere was taken off: Where it would continue till the Stem was broke open again, and then the Wa∣ter would be further depressed; as the weight of the Atmosphere was able to over-power the Resistance made by the internal Air.

Having made use of such a Vessel (as Fig. 7. Plate 1.) represents and conveyed a pretty Quantity of Water into both the Legs,* 1.10 we seal∣ed up the end of the bent Stem; leaving so much Air above it, as we thought convenient: Which being done, we placed the Ball of it in a frame, in which, the Tube hanging down, we could cover the round Ball with Snow and Salt: Upon which the Air in the Stem was able to expand it self so far, that the Water in the longer Leg was raised the length of a Barly-corn higher than before, and depressed as much in the o∣ther: But when the end of the Stem was broke open, the Water was raised 2 ¼ Inches in the longer Leg, and depressed so low in the shor∣ter, that several Bubbles rose into the Cavity of the Ball.

In which Experiment it cannot be supposed, That the weight of the Water in the shorter Leg could be able, to raise the Water in the other, except by Virtue of it's Spring, which being

but small, answerable to the Quantity of of it; it cannot be expected that it should have any con∣siderable Effect upon the Air in the other Leg; tho' it's Spring were in some measure weaken∣ed by Cold.

An Explication of the Figures in the first Plate.

• Fig. 1. p. 12.
  • A. The Ball or Egg.
  • B C. The Stem.
  • D. The little Aqueous Cylinder.
• Fig. 2. The open Weather-glass mentioned p. 16, 22.
• Fig. 3. The Sealed Weather-glass, or Ther∣moscope mentioned p. 16.
• Fig. 4. The Barometer or Mercurial Stand∣ard placed in a Frame B B. mentioned p. 17.
• Fig. 5. An Instrument mentioned p. 34.
  • A. The Vial.
  • B C. The Pipe cemented into the neck of the Vial, open at C and sealed at B.
• Fig. 6. p. 35.
  • A. The Bolt-head.
  • B. The small Stem.
  • B C. The Cylinder of Water enclosed.
• Fig. 7. p. 36.

Notes

• * 1.1

  The Opini∣on of the Schools con∣cerning the ascent of Water in Weather-glasses exa∣mined.
• * 1.2

  Experi∣ments al∣ledged a∣gainst their Doctrine.
• * 1.3

  See Plate 1. Fig. 3.
• * 1.4

  Mr. Hobbes his Doctrine examined.
• * 1.5

  A Modern Opinion ex∣amined.
• * 1.6

  and the Au∣thor's pro∣posed.
• * 1.7

  See Plate 1. Fig. 5.
• * 1.8

  See Plate 1. Fig. 6.
• * 1.9

  See Plate 1. Fig. 7.
• * 1.10

  See Plate 1. Fig. 7.