174- Mr. J. P. Joule on the Mecha?iical Equivalent of Heat. 

 Table I.— Friction of Distilled Water. 



We see then that the weights of 29 lbs., in descending 

 through the altitude of 1265'13 inches, generated 0°-668 in the 

 apparatus. But in order to reduce these quantities, it became 

 necessary in the first place to ascertain the friction of the pul- 

 leys and that of the twine in unwinding from the drum. This 

 was effected by causing the twine to go once round a roller of 

 the same diameter as the drum, working upon very fine pivots, 

 the two extremities of the twine being thrown over the pul- 

 leys. Tlien it was found that, by adding a weight of 3150 

 grain.s to either of the two weights, the friction was just over- 

 come. The actual force employed in the experiments would 

 therefore be 40G000 grs. —3150 grs. = 402850 grs. through 

 1265*13 inches, or 6067*3 lbs. through a foot. 



The weight of water being 77617 grs., that of the brass 

 paddle-wheel 24800 grs., the copper of the can 11237 grs., 



