1865.1] The Proposed Pendulum Operations for India. 251 
On the Pendulum operations about to be 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, 2. 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 are, 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 are 
by Arago, Biot and Mathieu 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 
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