THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



DECEMBER 1858. 



XLV. On the Figure of the Indian Meridian. By the Venerable 

 John Henky Pratt, M.A., Archdeacon of Calcutta. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IT is not many days since I had the opportunity of seeing for 

 the first time the Notices of the Royal Astronomical Society 

 for Januaiy 9, 1857, which contain a paper with the following 

 title, " An Examination of the Figure of the Indian Meridian as 

 deduced by Archdeacon Pratt from the two Northern Indian 

 Arcs ; with a proposition for testing that form by Astronomical 

 Observations, by Lieut. J. F. Tennant, Bengal Engineers, 

 F.R.A.S.;" and also a continuation of that paper, read before 

 the Astronomical Society in June of last year by the same author. 

 The calculation here referred to by Mr. Tennant was made by 

 me while at the Cape of Good Hope in 1854, and is published 

 in the Philosophical Transactions of the following year. As the 

 calculations and results of that paper do not appear to have 

 been altogether understood by Mr. Tennant, I trouble you with 

 these remarks*. 



2. The general figure of the earth has been determined to be 

 an oblate spheroid of elUpticity about ^ijj. This has been 

 arrived at by four distinct processes. (1) Upon the hypothesis 

 that the earth was once fluid, and by assuming a (very probable) 

 law of density of its mass, the depression has been brought out 



* I am indebted to Mr. Tennant for nointing out a numerical error near 

 the close of my paper. Others also, which I have detected myself, I have 

 corrected in another communication which I have recently transmitted to 

 the Society in the hope tliat they may consider it worthy of a place in their 

 ' Transactions.' These errors do not, however, at all affect my main results. 



Phil. Mag. S. 4. Vol. 16. No. 109. Dec. 1858. 2 D 



