JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. IV MAY 19, 1914 No. 10 



GEOPHYSICS. — Isostasy in India. ^ William Bowie, Coast and 

 Geodetic Survey. 



The investigatiorivS carried on by the United States Coast and 

 Geodetic Survey m recent years have proved conclusively that 

 for the total area of this country isostasy is practically perfect. 

 The two reports on the gravity reductions show that areas in the 

 United States of much smaller extent than the whole are largely 

 compensated. This is clearly showTQ by the gravity anomaly 

 map in the last gravity report. ^ But the area of the United States 

 is a small percentage of the land surface of the earth and the 

 scientist may well reserve judgment as to whether complete 

 isostasy obtains generally until the theory has been tested in 

 other lands. It is the earnest hope of advocates of this theory, 

 and even of its opponents, that such tests may be undertaken in 

 the near future. The determination of the dimensions of the 

 mean figure of the earth (the ellipsoid) and the actual shape of 

 the earth's surface (the geoid) are problems which the truth or 

 falsity of the theory of isostasy will help the geodesist to solve. 

 The degree of rigidity and the strength of the earth's crust may 

 be more closely estimated or computed after knowing more about 

 isosta.sy, and this is a very important matter to the geologist, the 



' Paper read in abstract before the Philosophical Society of Washington on 

 April 11, 1914. 



- Illustration Xo. 2, Effect of Topography and Isostatic Compensation on the 

 Intensity of Gravit3\ Special Publication No. 12, U. S. Coast and Geodetic 

 Survey. I 



245 



