1 1G 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 Trigonometrical 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 heg to present to the Asiatic Society a 

 complete set of my papers on this subject hound 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 30th, 1862. Jonisr 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 me 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 subseqiient 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 ]852, 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 



