122

Pneumatics.

Since the Particles of Air are such **being separated from Bodies beyond l

Sp* 1 ^

, ,

are affected by the Power of the Earth’s Attraction,rnuit therefore all gravitate or tend towards its C ein ^which is what constitutes Weight in them, 3,1 .Jtother Bodies. The Experiments to shew theW"e>sj^of the Air are numerous which we thew on thePump, among which one is absolute and very exact, a j|weighing it in a Balance, in the same manner aSother heavy Bodies are weigh’d. A

2. The Method I take for this is, I believe, th e j#exact and nice that can possibly be thought of. \$since (as we have Ihewn) the Friction of the Bala sl ^ ( j )in Proportion to the Weight with which it is chah^Jthe less the Weight is the less will be the Friction, £ jjCconsequently the more nice and exquisite will b®Experiment. In order to this I take a very thin ^Florence Flask, whose Capacity is exactly knCubic Inches: This I exhaust of all the Air as n^^can be, and then hang it to the end of a veryexact Hydrostatic Balance, which I counter-balan j,Grain-Weights in a Scale hanging from theoth"When the Equilibrium is nicely obtain’d, I list i*Valve, and let the Air rush into the Flask, wh' csensibly heard, and seen to gravitate in the Glf^’^iOcausing it gradually to descend till it be fill’d '" fand will then preponderate greatly. Then to T’, i 0

which shews that a Gallon of Air weighs about a ifand a Bushel an Ounce Troy ; and because one y 1 jjC 128 Cubic Inches nearly, therefore one Cubic I* 1Air weighs | of a Grain, at a Mean. ... pfj3. As the Air is a heterogeneous Fluid, it tvr $in its Weight according to its differentParts, and also according to its different Altitudes, gj it c cif must have as an elastic and fluctuating Fluid-few Bodies are lighter than Water, and thatis most .easily rarified into Vapour, it follows, *Atmosphere fill’d with aqueous Particles will he hS ^

the Equilibrium, I find by Experience ’tis neceÆ 31 ^)add about 8 Grains for every Pint the Flask

\