103 
for ascertaining the velocity of sound. 
experiments were made. The situations of the guns with re- 
spect to the station from which the observations were taken, 
was very favourable, being in the direction, one of N. E. and 
the other of the S.W. monsoons — with the southerly wind 
and sea breeze, (both which prevail at certain seasons of the 
year,) blowing between the two. The guns used were 24 
pounders, charged with 8 lbs. of powder, and both pointed, 
not exactly towards the station, but in a direction not far 
from it. 
The distances were ascertained with great care : first, by 
a survey made for the purpose, a base having been measured, 
and the angles taken with a grand circular instrument, simi- 
lar to that used on the trigonometrical surveys.* Secondly, 
by using two or three of Colonel Lambton's distances and 
bearings found by the trigonometrical survey. 
The results were thus deduced, and verified in different 
ways ; and I have reason to think that the distances of the 
guns from the Observatory station are very accurately given. 
The mean of 1 2 results made the distance of the Mount Gun 
from the station 29547 feet ; and the mean of 6 results, gave 
the distance of the Fort Gun from the station 13932,3 feet. 
The map-f will show the exact relative positions and distan- 
ces of the points, and the face of the country over which the 
sound travelled. 
* I have not given the details of the survey, as that would swell the Paper to an 
inconvenient size : the base, however, was measured with great care twice, and gene- 
rally six observations were taken for finding each angle, each observation differing 
very little from the other. 
f The angles and distances were protracted, and the map of the intermediate 
country filled up from the best surveys, under the superintendance of E. Lake, Esq. 
of the Madras Engineers, my son-in-law. 
