146 
Local Attraction. 
[No. 2, 
Memorandum, showing the final result of Archdeacon Pratt's cal¬ 
culations regarding the effect of Local Attraction upon the opera¬ 
tions of the Great Trigonomctrical Survey of India. 
To the Secretary of the Asiatic Society of Bengal. 
Dear Sir, —Having now received from London some copies of the 
last of my communications to the Royal Society on the amount of 
local attraction in India and its effect on the operations of the 
Trigonometrical Survey, I beg to present to the Asiatic Society a 
complete set of my papers on this subject bound up in one volume, 
and to request you to give insertion in your Journal to the following 
Memorandum, which gives a brief history of the circumstances con¬ 
nected with this investigation and of its final results. 
I am, yours faithfully, 
Calcutta , April 30 th, 1862. John H. Pbatt. 
Memorandum. 
The influence of Mountain Attraction upon the position of the 
plumb-line and of the spirit-level in the operations of the Great 
Trigonometrical Survey of India was first pointed out to mo by the 
Surveyor General in 1852, who on that occasion requested me to 
turn my attention to the subject. The result has been a series of 
papers which have been published in the Transactions of the Royal 
Society for 1854, 1855, 1858 and 1861. During the nine years over 
which the investigation has extended, new information has been ob¬ 
tained from time to time, and new suggestions have presented them¬ 
selves to my mind. Some things which had been published in one 
paper have had to be modified in a subsequent one, and the object of 
this Memorandum is, now that the series is complete, to state what 
is the final result of the investigation. 
2. I will give a brief historical sketch of the circumstances con¬ 
nected with the publication of the successive papers in the Philoso¬ 
phical Transactions. 
The Surveyor General of India pointed out to me in 1852, that in 
the volume published by his predecessor Colonel Everest in 1847, 
giving an account of the measurement of the two northern portions 
of the Great Arc between Kaliana and Kalianpoor, and Kalianpoor 
and Damagida, lying in the longitude of Cape Comorin, the observed 
