GEOGRAPHY. 347 



cent work in India gives a still larger fraction, assimilating 

 to the value heretofore obtained from pendulum observations. 

 The data on which the recent investigation is founded 

 are: (l) the latitudes of 13 stations in the Russian arc of 

 25 ; (2) latitudes of 15 stations in the Anglo-French arc of 

 22; (3) latitudes of 14 stations in the Indian arc of 24; 

 (4) the longitudes of 7 stations in India; and (5) the Cape 

 of Good Hope and Peruvian arcs. From these data equa- 

 tions of condition are derived, which by the method of 

 least squares give 



= 20926202, 

 c = 20854895, 



a and c being the equatorial and polar semi-axes in feet of 

 the spheroid most nearly representing the figure of the earth. 

 If, however, the more probable hypothesis of an ellipsoid in- 

 stead of a spheroid be assumed, the following are the values 

 of the semi-axes in feet : 



= 20926629, 

 5 = 20925105, 

 c = 20854477; 



and taking the ellipticity as the ratio of the difference of the 

 semi-axes to half their sum, the ellipticities of the two prin- 

 cipal meridians are ^ji and ^sTr 



Three well-determined secondary meridians Aden, Bom- 

 bay, Madras have been established by the Indian Survey 

 through the submarine telegraph cables ; telegraphic time- 

 signals having been exchanged by Major Campbell and Cap- 

 tain Heaviside between Bombay, Aden, and Suez, the longi- 

 tude of the latter station having been determined telegraph- 

 ically under direction of the Astronomer Royal on the occa- 

 sion of the transit of Venus in 1874. 



The whole work of the Indian Survey is carried on with 

 energy. Besides the geodetic work, a report is made of ex- 

 plorations by the native officials. During 1876 one of the 

 survey explorers, known as the Mullah, made an examina- 

 tion of the only part of the course of the Indus which re- 

 mained unexplored, from the point where it enters the plains 

 of Attok to where it is joined by the river Gilghit. Here 

 the river traverses a distance of about 220 miles, descending 



