292 ATMOSPHERICAL PRESSURE. 



SO tlio-t it requires some days or weeks before the 

 weight passes from one extreme to the other. 

 On an average the weight or pressure of the 

 atmosphere amounts to 14| lbs. on each square 

 inch of surface of the earth; and, as fluids press 

 equally in all directions, every square inch of 

 surface, whatever may be its position, must be 

 subject to the same pressure. The surface of the 

 human body, as well as that of animals in gene- 

 ral, has to sustain this pressure; and it will be 

 found by calculation, that the whole surface of 

 a middle sized person will have to support from 

 15 to 20 tons of pressure, all acting inwards 

 and having no other mechanical tendency than 

 that of squeezing or compressing the materials 

 of which the body is composed into a less com- 

 pass. 



The above is a statement of facts, all of which 

 I believe are allowed to be incontrovertible. But 

 a very difficult question arises out of them, — how 

 is it that the animal frame is utterly insensible of 

 the whole, or of any part of this enormous 

 pressure upon it. In ordinary we feel no pres- 

 sure on the surface of our bodies, either external 

 or internal, neither when the barometer is sta- 

 tionary nor when it is in a most fluctuating state. 

 I have never met with a satisfactory answer to 

 this question, and I doubt whether such a one 



