the Heat excited by Friction. 487 



duced by the friction of the borer against the bottom of 

 the cylinder was collected, and, being carefully weighed, 

 was found to weigh 4145 grains, or about 8f oz., Troy. 



As this quantity was produced in i\ hours, this gives 

 824 grains for the quantity produced in half an hour. 



In the first experiment, which lasted only half an hour, 

 the' quantity produced was 837 grains. 



In the experiment No. I, the quantity of Heat gener- 

 ated in half an hour was found to be equal to that which 

 would be required to heat 5 lb., avoirdupois, of ice-cold 

 water 180 degrees, or cause it to boil. 



According to the result of the experiment No. 3, the 

 Heat generated in half an hour would have caused 5.31 

 lb. of ice-cold water to boil. But, in this last-mentioned 

 experiment, the Heat generated being more effectually 

 confined, less of it was lost ; which accounts for the dif- 

 ference of the results of the two experiments. 



It remains for me to give an account of one experiment 

 more, which was made with this apparatus. I found, by 

 the experiment No. i, how much Heat was generated 

 when the air had free access to the metallic surfaces which 

 were rubbed together. By the experiment No. 2, I 

 found that the quantity of Heat generated was not sen- 

 sibly diminished when the free access of the air was pre- 

 vented ; and by the result of No. 3, it appeared that the 

 generation of the Heat was not prevented or retarded 

 by keeping the apparatus immersed in water. . But as, 

 in this last-mentioned experiment, the water, though it 

 surrounded the hollow metallic cylinder on every side, 

 externally, was not suffered to enter the cavity of its 

 bore (being prevented by the piston), and consequently 

 did not come into contact with the metallic surfaces where 

 the Heat was generated ; to see what effects would be 



