﻿ACROSS THE PENINSULA OF INDIA. 30,1 



of not being certain as to the exact height above the 

 level of the sea, since that height was determined by 

 corresponding barometrical observations made at 

 Madf^as, and at each extremity of the base, and I am 

 well aware tliat those results will be exceptionable. 

 But I was careful to found my computations on 

 those observations only which were made when a 

 perfect uniformity in the state of the atmosphere 

 had existed for several days together ; that is, when 

 the barometer and thermometer at each place, and 

 at the same hour of the day, had suffered scarcely 

 any sensible variation for a considerable time. And 

 since the quantity to be deducted from the base on 

 account of the height is little more than 8^ 5 feet, 

 upon the whole, any error that might arise in cor- 

 recting for the temperature and density of the at- 

 mosphere would be but trifling ; I shall therefore, foi* 

 the present, rest satisfied until the height can be de- 

 termined trigonometrically, and proceed to give an 

 account of the operations of the measurement, and 

 of the apparatus made use of. 



CHAIN, 



The chain is of blistered steel, constructed by 

 Mr. Ramsden, and is precisely alike, in every re- 

 spect, with that used by General Roy in mea- 

 suring his base of verification on Rurmiey marsh. It 

 consists of 40 links of ^4 feet each, measuring in the 

 whole 100 feet. It has two brass register heads, 

 Avith a scale of six inches to each ; these scales slide 

 in the brass heads, and are moved by a finger screw, 

 for the purpose of adjusting exactly the two extre- 

 mities of the chain when extended : in short, every 

 part of it is the same as the one above mentioned, 

 which has been fully described in the Philosophical 

 Transactions of 17i}0,.and therefore it is unnecessary 

 to say more on the construction of that instrument 

 here. 



Y la- 



