BOWIE: ISOSTASY IN INDIA 247 



geophysicist, the seismologist, and the astronomer. There are 

 other branches of scientific research to which this question of 

 isostasy is also of interest and importance. 



Gravity reductions made by the older methods, the Free Air, 

 which ignores topography, and the Bouguer, which postulates a 

 rigid earth with the topography as an added load, do not give any 

 definite idea as to the strength of the earth's crust. It is believed 

 that the new (Hayford) method does give valuable information 

 on this question. 



In India and Italy gravity stations are being reduced by the 

 Hayford method and it is the work already done in the former 

 country that is the basis of this paper. In the Report of the Board 

 of Scientific Advice for India for 1912-13, there are given the 

 results of the reduction of fourteen gravity stations which throw 

 some light on the question of the degree of perfection of isostasy 

 in India. These stations are in approximately the same longi- 

 tude and extend from latitude 23° 16' to latitude 28° 19'. The 

 report gives the data for the fourteen stations listed in table 1. 



The theoretical value of gravity, 70, shown in table 1, is ob- 

 tained from the Helmert formula of 1884, which is 

 70 = 978.00 (1 + 0.00531 sin^ 0) 



The means of the anomalies of the several methods of reduction 

 without regard to sign are: Free Air, 0.031; Bouguer, 0.012; 

 Hayford, 0.035; The means with regard to sign are: Free Air, 

 +0.029; Bouguer, -0.008; Hayford, +0.035. 



These values of the anomalies with regard to sign for the several 

 methods of reduction, and by the old Helmert formula, indicate 

 the presence of systematic errors in the reductions, though the 

 Bouguer method seems to be the one most nearly free from such 

 errors. 



The constants in the new Helmert formula (1901) are derived 

 from many more gravity stations and much more accurate data. 

 This formula is 



70 = 978.030 (1 + 0.005302 sin' 6 - 0.000007 sin^ 2 <f>) 



When the 1901 formula is used to obtain the theoretical value 

 of gravity at sea level and at the latitude of the station the sea 

 level values and the anomalies are those shown in table 2. 



