1862.] Proceedings of the Asiatic Society. 539 



Walker observed that the Archdeacon had thus rendered a second ser- 

 vice to the survey by demonstrating the presence of an additional, 

 but beneficial source of disturbance, tending to counteract the errors 

 which the Himalayas acting above, would introduce into the astrono- 

 mical arcs. 



A vote of thanks was accorded to Major Walker for his valuable 

 communication. 



Archdeacon Pratt, who was present, said that it was gratifying to 

 him to learn from so high an authority as the Superintendent of the 

 Gre.at Trigonometrical Survey himself that his investigations were 

 considered useful. His connection with this subject had arisen from 

 the accidental circumstance of his visiting Budraj near Dehra, ten 

 years ago when on a tour of official duty, on which occasion Sir 

 Andrew Waugh called his attention to the discrepancy which his 

 predecessor had found to exist between the measured and observed 

 lengths of the northern portions of the great arc of meridian, and 

 asked him to turn his thoughts to the subject. The investigation is 

 so difficult and abstruse that those only who had read his papers 

 through would enter into it. To this he would attribute the impres- 

 sion which had gone abroad in some places that in his fourth and last 

 paper in the Royal Society's Transactions he had in a measure reced- 

 ed from a position he had taken up in an earlier stage of the 

 investigation ; which was not at all the case. There could be no 

 question that the deflection caused by the Himalayas at the northern 

 extremity of the great arc is very great, about five times as great as 

 that caused at Col. Lambton's station, which was rejected in 

 consequence of the amount, as Major Walker has stated ; and that 

 there is a considerable deflection also at the southern extremity of the 

 arc, arising from a cause which had never before been thought of, viz., 

 the deficiency of attracting matter in the ocean, and amounting, there 

 was little doubt, to as much as four times the error at the rejected 

 station. At intermediate places on the arc the effects were inter- 

 mediate also. The tendency of the two causes taken together was, 

 therefore, as Major Walker had stated to a certain degree to equalize 

 the total error throughout the arc, that is in fact to conceal it, 

 because the Survey brings to light only relative errors of deflection. 

 His last paper had demonstrated by means of the theorem to which 

 Major Walker had referred, that (inappreciably small quantities being 



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