1862.] Proceedings of the Asiatic Society. 589 
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 
(Ireat 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 w r ould 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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