So 



THE POPULAR SCIENCE MONTHLY. 



It will be observed that since the diagonal either of a square or 

 of a parallelogram is longer than either of its sides, the resultant, A D, 

 will have a greater intensity than gravity represented by A B. Now, 

 suiDpose the point A' to be some point inside the earth's crust, and some 



distance from the surface, and suppose also that it is a particle of 

 water in a body of water imprisoned by surrounding rocks. This par- 

 ticle will be acted upon by a continual impulse to raove in the direc- 

 tion A' F', with an intensity represented by A' D'. This will be true 

 of every other water-particle in the imprisoned body of water. 



If, now, in an hermetically sealed vessel of water a set-screw is 

 turned and pressed upon the water inside until the resistance to it is 

 equal to one pound, that one-pound pressure will be duplicated upon 

 every other equal space of the vessel : and thus, if the end of the screw 

 has one square inch of surface, every square inch of the inside of the 

 vessel M'ill feel a pressure of one pound. Exactly this Avill occur in 

 the case of the water imprisoned in the rocks. The resultant of the 

 two natural forces, centripetal and centrifugal, will be duplicated upon 



