392 



Report of the Great Trigonometrical Survey. [No. & 



on the circumstances ; the proceedings of the Court have already been 

 submitted to Government. The Court came to the opinion, in which 

 I entirely concur, that the fall of the tower was occasioned by the 

 sudden and unexpected sinking of the ground below, and that no 

 blame is attributable to Captain Haig, or any other person, for the 

 mishap. 



Captain Haig had already turned out a very excellent season's 

 work, comprising thirty-two principal triangles, covering an area of 

 6,625 square miles, and extending over a length of 260 miles, whereof 

 66 appertain to the Mangalore meridian, and 194 to the parallel of 

 Bombay. 



The Spirit-Levelling Operations were carried on by Mr. Don- 

 nelly, Civil Second Assistant, under the superintendence of Lieutenant 

 Thuilher. The party accompanied me to Calcutta, to receive the 

 necessary instructions regarding the programme of the season's oper- 

 ations, which could not be decided on until I had obtained reliable in- 

 formation regarding the Railway levels between Calcutta and Agra. I 

 had hoped to be able to incorporate these into our work, so as to avoid 

 the labour and expense of carrying a line of levels all that distance. 

 During the previous Field Season, a connection had been made, at Agra, 

 with the Railway levels brought up from Calcutta, and the Trigono- 

 metrical Survey levels, brought up from the mean sea level at Karachi. 

 The two sets of results differed by about twenty-four feet, and it was 

 hoped that all difference would disappear, on connecting the Railway 

 datum, the site of Howrah Dock, with the mean sea level of the Bay 

 of Bengal. 



That level had already been closely ascertained, by a Series of 

 Tidal Observations taken at Kydd's Dock, and subsequently verified 

 by others taken at Kejiri, from the description of which (vide foot- 

 notes, next page,) it is evident that the mean sea level of the Bay of 

 Bengal may be considered to be known to within a few inches of the 

 truth. On connecting the Railway levels with Kydd's Dock, it was 

 found that there still remained a difference of about twelve feet between 

 the Railway and the Survey height of Agra. On discussing this subject 

 with the Chief Engineer of the Railway, I ascertained that there were 

 several breaks in the Railway levels, that, in consequence of the pres- 

 sure of other work, there had been no opportunity of preparing a 

 correct and true section of the whole line, and that it was contemplate 



