TRIGONOMETRICAL SURVEY OF INDIA. 



209 



having been lent for the occasion by the Chairman, and it is of importance 

 to remark, that two of the Gentlemen of the Royal Engineers who had 

 taken a prominent part in the measurement at Loch Foyle, Lieutenants 

 Drummond and Murphy, were with me for two days, in order that no 

 important step of the operation might be overlooked. 



Having measured the nine sets of bars in question, I returned over 

 the same ground, and on reaching the register from which I had originally 

 started, the return measurement exceeded the prior one by ^V^h of an 

 inch. Now -^^th of an inch in five hundred and sixty-seven feet, would 

 amount to 5 6 inches in eight miles, and to one hundred and forty-five 

 inches in a section of the meridian of about three degrees. 



The increments of degrees between the latitudes of 8" and 31° vary 

 from 5-2 to lO'O fathoms; if therefore we could be certain that this were 

 the greatest quantity to be feared, there could be no doubt, philosophically 

 considered, that the compensation bars would be quite adequate to the 

 purpose for which they were designed, and that the superior accuracy 

 attainable from them, would be commensurate with the greater toil entailed 

 by their use, and the increased expence and complexity of their structure. 



It is my opinion that the variation of -Vth of an inch is rather more 

 than need be apprehended, because the formation of Lords' Cricket 

 Groimd is a thick clav, which retains the moisture at the surface, and as 

 for several days of the operation rain descended in great quantities, there 

 was an alternation of dryness and Innnidity niiich more unfavourable than 

 need be looked for in actual measurement on a <;reat scale. 



In fact tlie constant trnnii)lin'4 of tlio l'cc\ oi' \hc soldiers and otiiers 

 who were occu[)ie(l in \\\r work, rendered such parts as were hoUnu pcM-fect 

 swamps, and anc le deep in nuid ;ind water, wliilst llie move ele\aied fiarts 

 were hard and dry. 



