OUR PRESENT KNOWLEDGE OF ISOSTASY FROM 

 GEODETIC EVIDENCE 



WILLIAM BOWIE 



Chief, Division of Geodesy, United States Coast and Geodetic Survey, 

 Washington, D.C. 



For a number of years investigations have been made by the 

 Coast and Geodetic Survey upon the subject of isostasy. The first 

 work was done under the direction of Professor John F. Hayford 

 in connection with a study of the deflection of the vertical and the 

 determination of the shape and size of the earth. The later work 

 consisted of investigations of the effect of topography and isostatic 

 compensation upon the intensity of gravity. This work was 

 started by Professor Hayford, and the first report on it was made 

 to the International Geodetic Association. 1 The first comprehen- 

 sive report on this work was made by Professor Hayford and the 

 writer in Special Publication No. 10 of the Coast and Geodetic 

 Survey which appeared in 1912. 2 The investigations of gravity 

 and isostasy were continued under the direction of the writer, and 

 the results have been published in two reports, one appearing in 

 191 2 and the other in 191 y. 3 



As is well known, the theory of isostasy postulates that at some 

 depth below sea-level forces are in equilibrium and, therefore, that 

 each column of unit cross-section extending from the depth of 

 compensation to the surface of the earth contains the same amount 

 of matter; or, to be more exact, it may be stated that each column 



1 Geodetic Operations in the United States, igo6-g, a report to the sixteenth general 

 conference of the International Geodetic Association. Separate publication of the 

 Coast and Geodetic Survey (not numbered), 1909. 



2 Effect of Topography and Isostatic Compensation upon the Intensity of Gravity, 

 Special Publication No. 10, Coast and Geodetic Survey, 191 2. 



3 Effect of Topography and Isostatic Compensation upon the Intensity of Gravity, 

 Second Paper, Special Publication No. 12, Coast and Geodetic Survey, 191 2; Investi- 

 gations of Gravity and Isostasy, Special Publication No. 40, Coast and Geodetic Survey, 

 1917. 



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