Superintendent of the Trigonomeirical Survey of India. 255 



He has taken experiments at the following stations, which you will find 

 in the chart at the end of Everest's description of the measurement of the 

 Indian Arc, Dehra Doon, Nojli, Kaliana, Dateri, and Usira. At Dehra 

 Doon he took six sets of observations with each pendulum ; but finding 

 he could advance more rapidly than the observatories could be got ready 

 for him, at the subsequent stations he took ten sets of observations with 

 each pendulum. Each set was carried over eight to nine hours, from 

 9 A.M. to P.M. The pendulum was set in motion in the morning, the 

 coincidences were observed, and the thermometers and arc of vibration 

 were read hourly, until the set terminated in the afternoon. The first and 

 last coincidences will be used only for determining the number of vibrations ; 

 but the whole of the intermediate temperatures and arcs will be employed 

 for determining the corrections for temperature and arc. He was very 

 fortunate in his transits, only losing four nights in sixty ; complete sets of 

 observations were twice taken at Kaliana (the northern extremity of the 

 Indian arc) in December, when the temperature was lowest, and again this 

 month when it was highest ; the range was not so great as we had antici- 

 pated, being 58^ in the first instance, and 92° in the second, so that the 

 results will scarcely be applicable to the observations at Kew, where, to the 

 best of my recollection, the temperature was between 40° and 50° ; but 

 they will amply suffice for all the observations that are likely to be taken 

 in India. He endeavoured to observe at a constant pressure, but the 

 leaking of the cylinder prevented this ; however, the whole range of 

 pressure does not exceed 3 inches, and the average range is much less, the 

 maximum being b inches and the minimum 2. He is about to commence 

 a series of observations at jNIasoori, at an altitude of about 6800 feet above 

 the sea. He hopes to complete these during June, before the rainy season 

 sets in, when transits will be impossible. 



During the rains he will be employed in completing the calculations 

 connected with his experiments. By September I hope to be able to send 

 you the final results. 



He has had so much to do in surmounting the difficulties arising from 

 his new apparatus, that he could not manage to take any magnetic obser- 

 vations. In future, however, he hopes to be able to take these observations 

 regularly at each of his pendulum stations. 



I trust that you will be gratified with this account of his first year's 

 operations. No pains have been spared to secure results of the highest 

 possible value, and to reward the confidence you reposed in us, when you 

 suggested to the India Office that we should undertake these delicate and 

 difficult operations. 



Believe me, yours sincerely. 

 General Saline, P.R.S. J. Walker. 



VOL. XV. 



