THE STRENGTH OF THE EARTH'S CRUST 



229 



angle 6 below a point on the horizontal line; the latter to be 

 defined as at distance R from the intersection. 



Let the gravitative attraction of unit masses along this vertical 

 line upon any other point either in or outside of this line be repre- 

 sented by F. The horizontal component will be the force produ- 

 cing deflection of the vertical and may be represented by Fh. The 

 vertical component will give the acceleration of gravity due to the 

 unit mass and may be represented by Fv. Taking the unit mass 

 such that the constants will have a value of unity, the following 

 relations are deduced: 



Attraction of unit mass at depth D, upon a point at R: 



cos^ 6 



Fh= 



Fv = 



R' 



tan cos^ 

 R' 



For the intersection point, 



R and 0=0 and 



Fh — o 



Let the depth of the zone of compensation, 114 km., be taken as 

 unit distance, i . 00, and for purposes of discussion let points I, II, 

 III, IV be located on a vertical line at depth of 0.25, 0.50, 0.75, 

 and 1. 00 as shown on Fig. 6. Solving the equations for these 

 points and for various values of R gives the following tabulation: 



TABLE XVII 



Table of Relative Attractions 

 (Not in dynes per gram) 



