the length of the pendulum at Madras. 165 
The height of the pendulum above the level of the sea was 
27 feet ; the distance in a direct line to the sea being about 
4900 yards, or 2,784 miles. The country is flat ; the near- 
est elevation being St. Thomas's Mount, which is 9950 
yards, or 5,654 miles off, and rises but little above the ordi- 
nary level.* There is a range of low hills a short distance 
beyond St. Thomas's Mount ; and the Pulicat Mountains, 
which are of considerable elevation, are 39 miles off. The 
soil about Madras is composed of sand and blue mud, and 
this to as great depths as the wells have been sunk. I do 
not recollect any rock having been found. I have therefore 
used 0,66 as a multiplier to 0,095, the correction for 27 feet, 
which gives 0,06 to be added to the number of beats in 24 
hours. 
The last correction required was for the buoyancy of the 
atmosphere. Having no information relative to the specific 
gravity of the pendulum, I was obliged to determine it in the 
best way the limited means in this country afforded. This 
was done with a balance at a dispensary, and with the aid of 
Mr. Bruce, the proprietor of the establishment. The Madras 
water drawn from wells in the Black town here, and con- 
ducted into the cisterns in the fort, is considered among the 
purest in the world. This was boiled, and strained into a 
tin trough prepared for the purpose ; the pendulum also was 
securely and properly slung by means of brass wire, with the 
assistance of Mr. Gordon, jeweller, of this place. The wa- 
ter was at the same temperature with the atmosphere, and 
the experiments were made with every care. It may be 
unnecessary to detail them here ; I shall therefore proceed 
to the result, which was as follows : 
» About 150 feet above the level of the sea. 
