OUR PRESENT KNOWLEDGE OF ISOSTASY 



433 



When the researches in isostasy and in the deflection of the 

 vertical were started, it was assumed that the compensation of 

 topography was complete, that it was distributed directly under the 

 topographic feature, and that it was uniform with respect to depth. 

 This method of distribution vertically and horizontally was contin- 

 ued in the computations connected with the researches in gravity 

 and isostasy. The depth of compensation derived from investiga- 

 tions of the deflection of the vertical, which was considered to be 

 of the greatest probability, was 122.2 km. 1 



As it is probably true that the gravity anomalies may be due to 

 an erroneous depth of compensation, it was decided to compute a 

 new value for the depth, based upon gravity observations alone. 

 The results of these computations, with numerous tables, are given 



TABLE IV 



in Special Publication No. 40, and only the results need be given in 

 this paper. In the investigations from which were determined the 

 most probable depths from gravity determinations, there were 

 used only the 219 stations in the United States. It was impossible 

 to use the gravity stations outside of the United States because 

 of lack of detailed data. 



The depth 113. 7 km., the one derived in the first investigation 

 of The Figure of the Earth and Isostasy from Measurements in the 

 United States, was used in making the reductions for compensation 

 in the investigations of gravity. With the detailed information 

 obtained from the computations it was possible to obtain the effect 

 of the compensation for other depths. This was done by means of 

 certain factors. 



The mean anomaly with regard to sign for all the stations is 

 shown in Table IV. The means without regard to sign for all of 



1 See Supplementary Investigation in igog of the Figure of the Earth and Isostasy, 

 P- 54- 



