Estimating the surface of man's body to be equal to fifteen square feet, he sustains an atmospheric pressure of 32,400 lbs., or nearly fourteen tons and a-half. The mere variation of weight, arising out of the changes in the state of the atmosphere, may amount to as much as a ton and a-half.
"I therefore so run, not as uncertainly; so fight I, not as one that beateth the air."—Corinth. ix.
646. Why does not man feel this pressure?
Because the diffusion of air which, surrounding him in every direction, and acting upon the internal as well as the external surfaces of his body, and probably surrounding every atom of his frame, establishes an equilibrium, in which every degree of pressure counteracts and sustains itself.
647. What is the weight of air relative to that of water?
A cubic foot of air weighs only 523 grains, a little more than an ounce; a cubic foot of water weighs one thousand ounces.
648. What is the greatest height in the atmosphere which any human being has ever reached?
M. Gay Lussac, in the year 1804, ascended to the height of 23,000 feet.