308 H. O. WOOD SOME CONSIDERATIONS TOUCHING ON ISOSTASV 



in volume its vertical reduction of volume by compression; and this lat- 

 eral expansion would take place in all directions in the plane perpen- 

 dicular to the vertical. 



The difference between the horizontal and the vertical effects is given, 

 in elastic substances, by Poisson's ratio, and this varies tor most sub- 

 stances between 0.2 and 0.3. In seismologic computations the value fc: 



£aKTh'$ 5oHFAC£ 



Figure 1. — Diagram to illustrate Growth of Stresses with Depth 



I. Increase with depth of vertical stress from load. 

 II. Increase with depth of lateral stress from load. 



the earth's outer shell has been taken at 0.27. Consequently, above the 

 region of incipient potential yielding, the overlying load produces a cer- 

 tain lateral stress which is considerably less than the vertical stress from 

 the same cause, while below, in the region of ready potential yielding, the 

 lateral stress from load should be approximately equal to the vertical 

 stress, and the conditions may be considered approximately hydrostatic 



