476 Inquiry concerning the Source of 



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 experi- 

 . ment, is represented by Fig. 2. W is a strong horizon- 

 tal 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 cyl- 

 inder 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 at- 

 mosphere. 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 cylin- 

 der was nearly 2- inches. This borer, which is distin- 

 guished by the letter , 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 60 F. 



At the end of 30 minutes, when the cylinder had 

 made 960 revolutions about its axis, the horses being 

 stopped, a cylindrical mercurial thermometer, whose bulb 

 was T 3 ^- of an inch in diameter, and 3^ inches in length, 

 was introduced into the hole made to receive it, in the 



