animal, are contained various parts : some hard, as bone? t 

 some soft, as muscles ; and some fluid, as blood. Now 

 it is not possible that bones should be broke or displaced 

 in the body, unless the pressure lay heavier on one part 

 than another. If the pressure be so divided, that it 

 be equal all round, upward, downward, sideways, and 

 no part of the skin to be exempt therefrom, it is plain, 

 no fracture or luxation can follow. 



The same may be observed of the muscles and nerves* 

 which though soft, yet being composed of solid fibres-, 

 'do mutually sustain each other, and resist the common 

 weight. The same holds of the blood and other hu- 

 mours. As water is not capable of condensation, so 

 these liquids, while contained in these vessels, cannot be 

 forced out of them by an universal compression. Add 

 to this, that the air itself which is contained- in every 

 part or the body, is such a balance to the external air, 

 that no hurt can ensue from its pressure. 



33. Oil of vitriol, when exposed to the air, conti- 

 nually increases in weight. Let a phial of this stand 

 unstopped, and it will be constantly running over. Per- 

 haps the cause of this odd phenomenon is, tlie moisture 

 contained in the air, which this liquor^ a potential fire, 

 imbibes as greedily, as actual fire does nitre. 



34. At the height of forty-one miles, tlte air is so ra- 

 refied, as to take up three thousand times the space it 

 does here. At fifty-three miles high, it would be ex- , 

 panded thirty thousand times as much as it is here. 



At that distance, (as was observed) it is expanded into 

 three thousand times the space it occupies here. Arid 

 we have seen- it condensed into the sixteenth part of the 

 same space. It seems then, that the air is capable of 

 being condensed into the hundred and eighty thousandth 

 part of the space it would take up when free from pres- 

 sure. But what texture must it be of, to make it capa- 

 ble of this immense .expansion and contraction? How 

 imperfectly is this accounted for, by comparing it to 

 wool, cotton,, and the like elastic bodies. 



