ABSTRACTS 



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GEODESY. — The effect of topography and isostatic compensation upon 

 the effect of gravity. John F. Hayford and William Bowie. 

 Special Publication No. 10, Coast and Geodetic Survey, pp. 130, 

 with illustrations. 1912. 



The introduction of isostasy in the determination of the figure and size 

 of the earth from observed deflections of the vertical resulted in a marked 

 increase in the accuracy of the values deduced. It was logical that isos- 

 tasy should be considered in the reduction of gravity observations in 

 order that a corresponding increase in accuracy of the shape of the earth 

 might be obtained from these data. 



A preliminary report on the reduction of 56 gravity stations in the 

 United States, by the new method, was made to the International Geo- 

 detic Association at London and Cambridge in 1909 by Hayford. The 

 present publication is a complete report on the reduction of 89 gravity 

 stations in the United States. 



By the new method a correction is applied at each station for the 

 attraction of the topography of the whole earth and also a correction for 

 the isostatic compensation of the topography in addition to the correc- 

 tion for the height of the station above sea-level. The compensation is 

 assumed to be complete and uniformly distributed from the surface to a 

 depth of 113.7 kilometers. Ihis was the most probable limiting depth 

 as determined by the first investigation of the figure of the earth and isos- 

 tasy from measurements in the United States. The better value of 

 120 kilometers, obtained from the second investigation of the figure of 

 the earth and isostasy, was not available at the time the tables were 

 computed for the gravity reductions. 



The methods used in applying the effect of the topography and its 

 compensation are fully described and the necessary working tables are 



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