620 



III. " Rectification of Logarithmic Errors in the Measurements 

 of Two Sections of the Meridional Arc of India." In a 

 Letter to Professor STOKES, Sec. R.S. By Colonel EVE- 

 REST, F.R.S. Received December 22, 1858. 



It will be in your recollection, that some years ago, at the 

 request of the Court of Directors of the East India Company, I com- 

 piled from the General Report of the Great Trigonometrical Survey 

 of India, a work entitled " An Account of the Measurement of two 

 Sections of the Meridional Arc of India," executed by myself and 

 my assistants, an impression of which (printed in 1847) was presented 

 to the Royal Society. 



In reference to the work in question, I now have to mention that in 

 the computation of the meridional triangles (vide pp. 240 to 248) 

 there have been some errors committed in taking out the logarithms 

 of the twelfth triangle (p. 241) and the twentieth triangle (p. 243); 

 and as from the nature of that series, the purpose of which is to project 

 the sides of the principal triangles on the meridian, any such error 

 must run through all the computations subsequent to it, I have had 

 the whole series recomputed, and now forward for submission to the 

 Royal Society, a sheet containing a revised synopsis (vide p. 248), 

 such as it would have been, but for the errors adverted to, to which 

 it is my wish that the utmost publicity should be given. 



I must here say, that I owe the detection and correction of the 

 said errors entirely to the industry of Colonel Waugh, F.R.S., and 

 the able computing establishment at his disposal ; for myself it re- 

 mains only to urge, that though mistakes of this nature are not ere - 

 ditable, but, on the contrary, much to be regretted, yet it is all but 

 impossible for the chief of two departments, that of Survey or- General 

 of India, and that of Superintendent of the Great Trigonometrical 

 Survey of India, each involving a vast array of business peculiar to 

 itself, to enter into all the minutiae of computation ; I took the pre- 

 caution to have every portion of the work gone over by two com- 

 puters acting independently, and it is singular that both should have 

 fallen into the same errors. 



As the existence of these errors, in the instance of the northern of 

 the two sections or series A, would naturally lead to the supposition 

 that like errors might lurk in series B (pp. 46 to 53), an equally 



