210 AN ACCOUNT OF THE. 
W ootasTon’s improved thermometer will supercede the mountain barome- 
ters altogether. It has every advantage. I may here mention that on the 
20th of June, 1816, when in the snowy pass in Kanaur, it occurred to me 
to put the thermometer to this use, which I did, and the next day, after cross- 
ing over the ridge of the Himdlaya, I mentioned the circumstance in a letter 
to England, and observed the advantages to be derived froma it, if thermo- 
meters could be made portable, with a sufficiently long scale. I was quite 
ignorant then of Dr. Woouaston’s instruments, or that a thermometer had 
ever been thought of, as a proper instrument for measuring heights, and in- 
deed it is very strange, how little it has hitherto been applied to the purpose. 
4, Tue chain which was used as a standard of comparison in the mea- 
surement of the base was made for me by Troucuton. It is of steel, 
one hundred feet in length at the temperature of 62. and is composed of 
twenty links, each being five feet, they are strong and little liable to bend. 
It has the usual apparatus of forks and pins to keep it stretched, and index 
plates, intended to be fixed to a stand, to mark the termination of each chain’s 
length. I much regret that [ had not two such chains, that one might be 
used in the measurement, and the other kept as a standard, but as there 
‘was only one, it was thought best to use it only as a check on the cedar 
rods, as is fully detailed in the sequel, 
Tue above are the principal instruments used in the trigonometrical and 
astronomical operations of the survey, intended to determine the positions of 
the snowy peaks, but in tracing the numerous routes, and filling up the interior 
of the map, various instruments, adapted to the purposes, were employed, 
of which it is not necessary to give detailed descriptions, 
