(namely, that the Force with which the Air preffes upon all things is equal to that of a Column of Water of about 33 Foot in Height) is fhewn in all its Circumftances; and fo every one that represents the thing to himself, may confider the terrible Powers which, tho' he feels nothing of 'em, are continually exerting themselves upon, and round about him.

SECT. XI. The dreadful Preffure of the Air upon a Man.

Now to fhew the incredible Greatnefs of that Force which the Air exercifes upon our Bodies, let us for once fuppofe (it being too laborious and unneceffary alfo to defcribe the fame with the utmoft Exactness) that a Man of fix Foot in Height, is one Foot in Breadth from Top to Bottom, the broader and narrower Parts being reckon'd together; fo that the Superficies of his Body, both before and behind, may comprise 6 Foot each, the roundness of the Sides being counted in, if this Computation fhould feem too large.

Now according to what has been faid, every Foot in Breadth sustains as much Weight as if there were a Column of Water of 30 Foot at least upon it; we put 30 instead of 33 Feet here, because the Air has a different Weight at different Times, and the very smalleft of it will be a fufficient Proof of our Hypothefis.

And every Cubical Foot of Water weighs about 63 Pounds, as we have found it upon Trial, tho' others make it a little heavier, which may proceed from several Causes, such as the difference of Waters and Seasons, and of the mixture of more or less Air therein; but this is not material, for the fmalleft Weight is here the strongest Proof.

This

This then being fuppos'd, altho' this Preffure upon our Body is moftly fidewife, and (excepting that upon the Head) is rather a lateral than perpendicular Preffure; yet it is well known to those who understand Hydroftaticks, that by reason of the height of the Air, and the fmallnefs of a Foot with refpe&t thereto, there is little difference between the lateral and perpendicular Preffure ; and he that is no Mathematician may likewife experience the fame; because, whether he stands upright, or whether he lies all along upon the Ground (at which time the Air will prefs perpendicularly upon every part of his Body) he does not perceive the leaft Difference. From whence it then follows, that upon every Superficies of one Foot of our Body, there always lies a Weight of 30 times 63, that is, 1890 Pounds; and accordingly, upon 6 Foot, which we have fuppofed to be the Breadth of the Body, 6 times 1890, that is, 11340 Pounds, with which Weight our Body is preffed only before, or behind; fo that if you take the whole Force of the Preffure, which is equally fuftain'd on both fides of the Body, the whole Weight will amount to 22680 Pounds. Now to avoid any mistake, we will fuppofe it in round Numbers to be no more than 20,000 Pounds, which is certainly not too much.

SECT. XII. Convictions from the foregoing Obfervations.

Now could any Body have imagined, if this irrefragable Truth had not been demonstrated by the plainest Experiments, that when he thought he was free and felt nothing, he should be loaded upon every part of his Body before and behind with no lefs a Weight than that of 20,000 Pounds; and that nothing could have faved him from being crushed

crushed to pieces by fo terrible a Force, than that exact Balance of another Force against it; whereby the one operates juft as much in favour of us, as the other would do to our Prejudice.

Now that this most astonishing Force would be more than fufficient to crufh our Body to pieces, can be doubted by no Body; forafmuch as if the Preffure of 10,000 Pound Weight upon one fide fhould cease to refift or balance the like Weight on the other, our Body would feel the fame, juft as if a Weight of 10,000 Pound did press upon the forepart of it, not only flowly and gradually, which yet would be enough to deprive us of Life, but as much as if the like Weight of fo many Thoufand Pounds were fuddenly caft against our Body: For the Elaftick Power of the Air, if the Balance thereof be taken away, exerts its Preffure with a more terrible Velocity than can be imagined. Now fince every one of us is bound to acknowledge herein a Power preferving him every Minute from utter Destruction, and that the fame Power operates according to the Rules of a wonderful Wisdom; can we do otherwise than ascribe all this to an infinitely Wife Director? And if it cannot be deduced from ignorant Causes, let the Atheist confider with himself what he has to expect for fuch blafphemous Negations of fo wife and mighty a Being.

SECT. XIII. and XIV. Experiments fhewing the Preffure of the Air.

Now as ftrange as all this may appear to any Body, yet all they who are used to Pumps, know that it is true: For if on the Top of a round Brafs Veffel (Tab. XIII. Fig. 3.) which is open CD, you fix a flat Glafs A B, which is adapted to the upper Orifice thereof; and (to prevent

at

the

the entrance of the leaft External Air N, and mixture with that of K in the little Veffel) thro' the Paffage which is between the Glafs A B and the Circumference of the Veffel, it being ftopt with a mixture of Sheeps Suit and Wax, and fo fet down together upon the Brafs Plate HI, of the Air-Pump and its Leather; then the Glafs A B (like all others that are in the Air) will remain wholly unmoved between the equal Preflure of the oppofite Air at N and K, as is fufficiently known.

Now that this only happens on account of the exact Balance of both thofe Columns of Air, by means of which the Air at K preffes the Glafs upwards with juft as much Force as the fame is preft downwards by that at N, may appear from hence; forafmuch as when the Force of the Air at K is never fo little diminished by pumping out fome of it, one thall fee that the Column E ABF, of the external Air N, preffing upon the other fide of the Glafs, will not only burst it, but will break it all to pieces, with a Noife like the Difcharge of a Gun; which to perform in the like manner, would require a very great Strength and Swiftnefs in the blow of a Hammer.

The faid Force of the Air appears likewife by exhaufting as far as one can the Air out of a Globe of Glafs AB (Tab. XIII. Fig. 4.) and afterwards having turned the Cock E, by taking the fame off and placing it in a Veffel of Water LFGM, with its Orifice D downwards. Then turning the Cock E back again, whilft it is under Water, fo that the faid Water may enter into the Globe by the part DB; whereupon immediately as foon as the Cock E is open'd, the Air at H and K, gravitating or preffing upon the Water L M, which is on the outfide of the Tube D B, exerts its Force, caufing the Water to fpring thro' the Tube into the empty Globe with as much Vio

lence

lence and Swiftnefs as a Fountain, so that it will very much furprise those that have never feen the like.

Now the Cause thereof is, that by exhaufting the Air out of the Globe AB, the Oppofition or Refistance is likewife taken away; which otherwife, when the Globe is full of Air, does with equal Force withstand the Water to be driven up thro' the Tube D B, by the Preffure of the external Air at H and K, is plain from hence; becaufe we know that upon admitting the Air again into the Globe, and putting every thing in Statu quo, there will not be the leaft Motion difcover'd in the Water; which being preffed upwards and downwards with equal Force in the Tube B D, between the two Powers of the Air within and without the Globe, reciprocally acting upon each other, does confequently remain quiet, and, as far as it appears, without any fenfible Disturbance.

SECT. XV. Convictions from the foregoing Obfer

vations.

Now I fubmit it to any Body, who from what we have here faid has attained to a true Idea and Conception of thefe dreadful Powers of the Air, whether inftead of believing that all things in which he can difcover no Motion round about him, do remain at Reft; whether, I fay, he is not now convinced that he is every moment of his Life encompass'd with fuch a Force as acts upon him and every thing befides; and of which, if the Wisdom of the great Director did not hinder it by an Equilibrium, from exerting all its Strength upon him, the half only would fuffice to crufh him and every thing else breathing, to pieces; and confequently, whether he can imagine, that it is by mere Chance only, and without any Wisdom, that Vol. II.

C

while