Air, A C, over them, and confequently a leffer Weight, may be proved by the following eafie Experiment among others: Take the Tube of a Barometer (Tab. XIV. Fig. 1.) let it be open at I, and fhut at F; fill it with Quickfilver fo far as to leave a little Air at the Top of it; then ftop the Orifice I with the Finger H, and turn it fuddenly upfide down, so that the Finger which was before at the Top, may now be at the Bottom. This being done, you will fee that the Air that remained in the Tube, and which, by the inverting thereof, does now bear the Preffure of the whole Column of Quickfilver, will be immediately contracted into a much narrower space than it was at I; and that as it afcends thro' the Quickfilver from I to F, it will continually poffefs larger Spaces, because the incumbent Quickfilver does continually lofe of its Heighth above it; and therefore the higher thefe Air-Bubbles come, the lefs Weight they feel; and this is the reason why they appear to us larger at A than at I, at B than at A, at C than at B, and fo on, till they have got up as high as F, where being no longer preffed, they are expanded to the utmoft Bignefs.

We may likewife fee the fame Appearances, but with lefs difference of Size, if we fill the Tube with Water inftead of Quickfilver: From whence it may be then concluded, that the Air which bears the greatest Weight, is alfo the most compreffed.

1

SECT, XXI. Air that is moft Compressed, is most Elaftical.

Now that the Air that is moft compreffed, does make the strongest Efforts to dilate or expand itself again, and accordingly preffes more powerfully upon all the Bodies about it (befides, that the

C 4

fame

fame appears from the Wind-Guns, and the little Fountains of Hero Alexandrinus) may be prov❜d by a very eafie Experiment, (Tab. XIV. Fig. 2.)

Take a Syringe SD (thofe that are used in Anatomical Operations are, by reafon of the Narrownefs of the injecting Tubes, very fit for this purpose) and drawing out the Pifton SC half way as far as C, fo that the Part A B remains full of Air; put the End or Nofe of it D, in Water, which will enter into it,by drawing back the Piston to FG; then fcrewing upon it a little Tube D E, which has a fmall Orifice at E, if you lay the Syringe horizontally, so that the Water A may cover the Hole D, and the Air B remain over it, you will not be able to discover the leaft Motion therein; but if you fuddenly, and at once, protrude the Pifton from FG, to C, fo as to make the Water spout out at E, and the Air at B is the more compreffed thereby; tho' you fhould immediately ftop the Pifton again, you will yet find, that the Air at B being more compreffed, does likewife expand itself with greater Force, and preffes upon the Water A; fo that the Stream of Water E K, does thereby continue for a long time to run out at E, even tho' the Pifton do lie ftill at C, and preffes no farther; from whence what has been faid above is proved.

SECT. XXII. Convictions from the foregoing Obfervations.

Now, if any would contemplate the aforemention'd Laws, and how the formidable Power of the Air is fo wonderfully balanced by fo fmall a part of the fame; Can he still imagine, that all this is owing to Chance, without any Design or Wisdom of the Maker?

Without fuch a Law, and in cafe that the little Air which is in a Chamber could not fufficiently

balance

balance the vast Ocean of the external Air, how could it otherwise be, but that all our Glass Windows, like the Glass Veffel mention'd in §. xiii. should be immediately broken into small Pieces? Forafmuch, as according to the preceding Calculation §. xi. upon every fquare Foot thereof there is a continual Preffure of above 1800 Pounds Weight. Without this Law, how could an Army Tent, a Peafant's House, or a Shepherd's Cottage, yea even the most stately Edifices, remain ftanding? Since, if they be taken in their Largenefs and Circumference, as an Apartment, which being but ten Foot in Length, and of the fame Breadth and Heighth like a Dye, the four standing Sides, and the Ceiling, being each 100 Foot broad, and each pressed upon with 189,000 Pounds Weight, and confequently the whole Apartment would be preffed with five times as much Weight upon all its Sides, on which the Air is incumbent, that is to fay, with a Weight of 945,000 Pounds. Whereas in the fpace of 1000 Foot, which the whole Compass thereof contains, the whole Body of Air that refifts fuch an External Preffure, would not gravitate more than 63 Pounds; fuppofing, with many Enquirers, that a Cubic Foot of Water weighs 63 Pounds, and is a thousand times heavier than a like Foot of Air. Without this Law, how is it conceivable that we, who are continually preffed with a weight of above 20000 Pounds round about us, fhould not have been long fince crushed to Pieces, fince the third Part thereof is able to do it? And in case our Breast, by the Roundness of its Ribs and Cartilages, might make fome Refiftance, how comes it, that our Belly and Loyns are not preffed flat and close together by fuch a Force, were it not that they did contain fome little Quantity of elaftick Air, which, tho' fo very fmall, is yet able to balance fo terrible a

Preffure