the Source of the Heat excited by Friction. 85 
against it was equal to the weight of about loooolb. avoirdu- 
pois, the cylinder was turned round on its axis, (by the force 
of horses,) at the rate of about 32 times in a minute. 
This machinery, as it was put together for the experiment, 
is represented by fig. 2. W is a strong horizontal iron bar, 
connected with proper machinery carried round by horses, by 
means of which the cannon was made to turn round its axis. 
To prevent, as far as possible, the loss of any part of 
the heat that was generated in the experiment, the cylinder 
was well covered up with a fit coating of thick and warm 
flannel, which was carefully wrapped round it, and defended 
it on every side from the cold air of the atmosphere. This 
covering is not represented in the drawing of the apparatus, 
fig. 2. 
I ought to mention, that the borer was a flat piece of hardened 
steel, 0.63 of an inch thick, 4 inches long, and nearly as wide 
as the cavity of the bore of the cylinder, namely, 3^ inches. 
Its corners were rounded off at its end, so as to make it fit 
the hollow bottom of the bore ; and it was firmly fastened to 
the iron bar (m) which kept it in its place. The area of the 
surface by which its end was in contact with the bottom of the 
bore of the cylinder was nearly 2^ inches. This borer, which 
is distinguished by the letter n 3 is represented in most of the 
figures. 
At the beginning of the experiment, the temperature of the 
air in the shade, as also that of the cylinder, was just 6o° F. 
At the end of 30 minutes, when the cylinder had made 960 
revolutions about its axis, the horses being stopped, a cylin- 
drical mercurial thermometer, whose bulb was of an inch 
in diameter, and 3^ inches in length, was introduced into the 
Gz 
/Jdooqo • 
'525 ^ 3' 3 
/'b203/ 
