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

EXPERIMENT XXXVI. The Weight of Air in the Exhausted Receiver. The subtle penetrating Power of some Spirits above that of the Air. The Cause why Air will not enter the Pores of some Bodies which Water will. The Weight of the Air, examin'd by an Aeolipile. The Proportion betwixt the Gravity of Air and Water: Betwixt Water and Quicksilver. Con∣jectures concerning the Weight of the Atmo∣sphere.

* 1.1NOtwithstanding the several Methods pro∣propos'd by Galileo, and others, to try the Weight of the Air; being willing to be fur∣ther satisfi'd, we caus'd an Oval Glass with a small Tube at one End to be blown at the flame of a Lamp. And this Glass Bubble, being of the size of a Hen's Egg, was fix'd to one End of a Balance, being counterpois'd by a Weight at the other End, which being suspended in our Receiver, and the Pump set on work, the Bub∣ble, after three Exsuctions, continu'd to prepon∣derate more and more, till the Air was let in again, and then the Balance was reduced to its former Aequilibrium. But having repeated the Experiment with an additional Weight of three Quarters of a Grain, in the Scale opposite to the Bubble, the Weight of the Air included in the Bubble brought the Balance to an Aequilibrium, when the Air was drawn out; which Aequili∣brium was again lost upon a reingress of it; so that had the Air been wholly exhausted, the Air contain'd in the Bubble might probably

have weigh'd a whole Grain; and to prove that the Weight of the Air did really depress the Balance to which the Bubble was fix'd, we ex∣hausted the Receiver when the Neck of the Bubble was open; and did not perceive that End of the Balance in the least to preponderate: But a Lamb's Bladder being equally pois'd with a correspondent Weight, manifestly weigh'd down the Balance, tho the Air included in it, was considerably expanded when the Air was pump'd out of the Receiver.

* 1.2But once having caus'd the Pump to be ply'd longer than ordinary, the Air contain'd in a Glass Bubble expanded it self so powerfully, as to cause the sides of it to fly in pieces; which is a strong Argument of the Closeness of the Pores of the Glass, which are too fine to per∣mit the Air to pass through them. And for a further Proof of the imperviousness of Glass, even by so minute Particles as those of the Air, I shall add; that in all the Tryals I ever made, I but once found that a Spirit whose Parts are much more subtle and volatile than Air; I say, I but once found that a Spirit drawn from a Substance abounding with volatile Salts, and subtle Spi∣rits, made way through the Pores of the Recei∣ver, which unusual Phenomenon probably de∣pended on the brisk Agitation of those spiritu∣ous Parts, encreas'd by the more than ordinary Heat with which they were rais'd; for the Mo∣tion of them was so violent, as to fill the Recei∣ver, and almost burst it with their impetuous Steams; so that the Pores of the Glass being open'd with the violent Heat, several of them

penetrated those Pores, and appear'd on the out∣side of the Glass.

* 1.3But tho' by some, the Particles of the Air are thought to be able to penetrate Glass; yet by o∣thers, they are thought to be Grosser than Wa∣ter; since from the following Experiment it ap∣pears, that Water is capable of penetrating Bodies, and of being compress'd into their Pores, which Air is not: For having conveigh'd a small Bubble of Water into the longer Leg of a Sy∣phon, whose Orifice was as small as a Pin, that Air being incapable of passing through so small a Pore, kept the Water above it, suspen∣ded in the Tube; but as soon as that Bubble, by blowing into the wider Orifice of the short Leg, was compress'd and squeez'd out, Water pass'd through that small Orifice without any other force than the Weight of that which lay upon it. And the Inability of Air to pass through such Pores, which Water will readily enough, will be further evinc'd, by holding Water in a Tube, the lower End of which being very narrow, and perforated with a Pore no longer than a Hair; for the Water will readily pass through it; but if the Tube be inverted, the Water in the narrower End of that Pipe will be suspended, as if the End were wholly unperfo∣rated; the Air not being able to get through so small a Passage: And that Water will pass through Pores, which Air will not, may be fur∣ther evinc'd, by putting a little Alkalizate Salt into a Lamb's Bladder; for by wetting the End of the Bladder on the outside, the Water passing through it's Pores, will presently dissolve that Salt.

* 1.4But to return to what we have hinted before, concerning the Expansion of Air in a Bubble, so violently, as to break it; the Learn'd Jesuit Cabaeus says, he saw a Pillar so thick, that three Men could not grasp it, and that 1000 Yoke of Oxen could not tear it in Pieces; yet the Air in∣cluded in the Crannies of it, so violently expan∣ded upon the burning of a Fire near it, that it flew in pieces, tho' the Pillar was made of so so∣lid Stones as Marble. And as for the Reason why sometimes the Bubbles included in our Re∣ceiver, did not break as at others, it probably pro∣ceeded from the Air's Expansion by Heat, when they were seal'd, the included Air, upon a Re∣moval of that Heat, contracting it self, and losing part of it's Springiness; but this Guess we can∣not wholly rely on. But,

* 1.5To determine more exactly the Weight of the Air, we heated an Aeolipile of Copper, as hot as we could conveniently; and removing it from the Fire, we stopp'd the Neck with hard Wax, to keep out the Air; which being Weigh'd, when cold, counterpois'd six Ounces, six Drachms and Thirty nine Grains; but the Air being permit∣ted to rush in, by perforating the Wax with a Needle, the Aeolipile and Wax balanced an ad∣ditional Weight of 11 Grains; so that the Weight of so much Air as fill'd the Cavity of it, weigh'd half a Scruple and a Grain. And tho' Mersen∣nus affirms, that he had rarifi'd the Air to seven∣ty times its Bulk in an Aeolipile, yet I must con∣fess it seems impossible to me, except the Metal his were made of, would bear a much greater Degree of Heat, without melting, than ours would, to rarifie, and expel the Air contain'd

in them: Besides, the Method he took seems much less exact than ours, since he weigh'd the Aeolipile whilst hot; which might throw off a Considerable Quantity of Scales, as we have often observ'd; the Weight of which, in weigh∣ing so light a Body as Air, might be considera∣ble.

* 1.6As for the Difference in the Weight of an e∣qual proportion of Air and Water, tho' Riccio∣lus and Galileo have, by different Methods, made very different Computations; and Mersennus hath asserted it to be as 1300 to 1. Yet by the most accurate Computation we could make in our Aeolipile the difference appear'd to be, no more than as 1 to 938. I shall not wholly reject what Mersennus relates, but rather endeavour to reconcile the Difference, by representing, that my Observations were not only made in this Climate in London, where it is much colder than at Paris; but also at a time, when the Air was condens'd by the Winter's Cold; at which time it may be suppos'd to be a fifth Part heavier than at Paris, when Mersennus made his Observa∣tions. Wherefore it would be of no small use, to make such Observations in several Countries and at several Seasons of the Year.

* 1.7Having said thus much about the Weight of the Air, it may perhaps be expected, that I should, by the Assistance of the Observations already deliver'd, determine the Height of the Atmosphere, from whence the Pressure of the Air proceeds: But tho' it may be no difficult Task to shew, that the Accounts given by others are false; yet it is not altogether easie to deter∣mine a Controversie, in which the Truth is so

hard to be assign'd; and therefore, I shall only lay down something in order to the Elucidation of it.

And first, it is necessary to take Notice, that the Weight of an equal Proportion of Air and Water about London is agreed on to be as 1000 to 1.

In the next place it will be requisite to consi∣der, the Difference in Weight, of an equal Pro∣portion of Air and Quicksilver; to discover which, I took a Glass Pipe, such as is represen∣ted by the Sixteenth Figure,* 1.8 which being partly fill'd with Quicksilver, and held in such a Po∣sture, that the Superficies of the Quicksilver in each Leg was in a Horizontal Line, E. F. I. pour'd Water into one Leg, till it was fill'd up to the Top, by the Weight of which, the Sur∣face of the Mercury was weigh'd down from E. to B. the Surface of the other being rais'd from F. to C. so that measuring the Height of the Tube of Mercury D. C. which was buoy'd up by the Water in the other, we found it to a∣mount to 2 13/54 Inches; the Height of the Cylin∣der of Water B. A. which counterpois'd the Mercury being 30 45/54 Inches, and the whole Num∣bers with the Fractions, being reduc'd to impro∣per Fractions of the same Denomination, the Proportion was as 121 to 1665, or by Redu∣ction, as one to 92/121.

Besides this, we took another Method, to di∣scover the Proportion of these two Liquors, by weighing them in a Glass Bubble; by which we found, that it was as 1 to 13 19/28; and because Spirit of Wine is usually esteem'd the lightest of Liquors, and Quicksilver the heaviest, I

weigh'd that likewise, and found the Proportion of Quicksilver, and it, to be as 1 to 16 641/1084. So that the difference betwixt Spirit of Wine and Water was as 1 44/171; And here it may be neces∣sary to observe, that I the rather weigh'd these Liquors in a Bubble; because, when they are weigh'd in open Vessels, the Protuberant Sur∣face of the Mercury, and the Concave of the Water, makes it a difficult Matter to propor∣tion them exactly, if the Superficies be large.

* 1.9But to return to the Atmosphere. Having laid down the Proportion of Air to Water, and of Water to Quicksilver, it will be no very diffi∣cult thing to find, the Proportion betwixt Air and Quicksilver. And since from the Torrecel∣lian Experiment, it appears that the Cylinder of Mercury is buoy'd up by the Pressure of the Air, it consequently follows, that the Proportion of Air to Quicksilver is as 14000 to 1; so that a Cylinder of Air, that is able to buoy up Mer∣cury two Foot and a half, must amount to 35000 Feet of our English Measure, or seven compleat Miles; supposing the Air to be equally com∣press'd above, as here below; but this Compu∣tation is not to be accounted so exact, since not only Seneca Nat. Quaest. lib. 4. cap. 10. says, Om∣nis Aer, quo propior est Terris hoc crassior; quem∣admodum in Aqua & in omni humore Faex ima est; ita in Aere spississima quaeque desidunt, but it like∣wise is a Consequence of the Air's Spring; since it must needs be considerably compress'd by the Weight of what lies upon it; besides, if we con∣sider, that the Air may be expanded by Heat, to near a hundred and fifty times its Bulk, it may not be improbable, but that the utmost ex∣tent

of the Atmosphere, may reach to some Hun∣dreds of Miles.

And this Conjecture may enable us to guess at the Height to which some Vapours may as∣cend, allowing what Emanuel Magnen a dili∣gent Mathematician observ'd at Tolouse in a clear Night in August; for as Ricciolus records it, Vidit ab Horâ undecimâ post Meridiem us{que} ad mediam Noctem Lunâ infra Horizontem positâ, Nubeculam quandam lucidam prope Meridianum fere us{que} ad Zenith diffusam, quae consideratis omnibus non poterat nisi à Sole illuminari; ideo{que} altior esse debuit tota Ʋmbra Terrae: And the same Author further says, Addit simile quid evenisse. Michaeli Angelo Riccio apud Sabinos versanti, nempe viro in Mathesi Eruditissimo.

But to conclude; It would be of no small Use in estimating the Height of the Atmosphere, were Observations of the Density and Rarity of the Air made upon several Parts and on high Mountains; but till by some Means or other, we can arrive at some degree of Cer∣tainty, as to the various Degrees of it's Rare∣faction above, it will be a hard Matter to de∣termine the Height of it.

Notes

• * 1.1

  The Weight of the Air.
• * 1.2

  The Pene∣trating power of some Spirits above that of the Air.
• * 1.3

  Why the Parts of the Air are more indispos'd to pass through the Pores of some Bodies than others.
• * 1.4

  The force of the Air's Expansion.
• * 1.5

  The Weight of the Air.
• * 1.6

  Proportion betwixt the Weight of Air and Water, &c.
• * 1.7

  Conjectures concerning the Height of the At∣mosphere.
• * 1.8

  See Plate the First.
• * 1.9

  The Weight of an equal Proportion of Air and Mercury.