1S65.] The Proposed Pendulum Operations for India. 251 



On the Pendulum operations about to he undertaken by the Great Trigo- 

 nometrical Survey of India ; with a sketch of the theory of their 

 application to the determination of the earth's figure, and an account 

 of some of the principal observations hitherto made. — By Capt. J. P. 

 Basevi 7 B. E., 1st Assistant, Great Trigonometrical Survey of India. 



[Received 29th July, 1865.] 



"Whilst Lieut. -Colonel Walker, R. E., the Superintendent of the 

 Trigonometrical Survey, was in England last year, General Sabine, the 

 President of the Royal Society, solicited his attention to the importance 

 of making a series of Pendulum observations at the stations of the 

 Great Indian arc, of a similar nature to those made by Captain Kater 

 at the stations of the English arc, and by himself, Captain Henry 

 Foster and others in various parts of both the Northern and Southern 

 hemispheres. Pendulum observations were made on the French arc 

 by Arago, Biot and Mathien early in this century ; it is also the inten- 

 tion of the Russian Government to have them made at the principal 

 stations of the Russian arc : moreover there is hardly an instance of 

 the measure of an arc which has not been accompanied by such observ- 

 ations. 



General Sabine offered to assist by placing at the disposal of the 

 India Board the pendulums, clocks, and apparatus which he had 

 employed in his own operations ; and he added that, should the India 

 Board desire any opinion from the Royal Society on the subject, he 

 would assemble a Committee for the purpose. 



Colonel Walker drew up a scheme and estimate of the probable 

 expense, and submitted it with General Sabine's letter for the approval 

 of the Secretary of State for India, who, acting on General Sabine's- 

 suggestion, requested the Royal Society to report on the plan of oper- 

 ations proposed by Colonel Walker. 



The President accordingly called for opinions from several distin- 

 guished Fellows, viz. Professors Challis, W. H. Miller, Stokes, H. J. S. 

 Smith, Dr. Robinson, Sir G. Everest, and Sir John Herschel ; all in 

 their replies were agreed on the scientific value of the operations, and 

 33 • 



