THEEMO-D YNA MFCS. 



3f> 



directions and heavy weights weighing from 10 to 30 Ibs. 

 were attached to the extremities of the strings. When 

 the apparatus was in perfect order there was very little 

 friction, because the strain of the string is equal in 

 the two directions. The quantity of friction there was he 

 was enabled to measure by an extremely ingenious process 

 with considerable accuracy. He let his weights descend 





to the floor from a distance of five feet, then he wound 

 the string up again without turning the paddles at the same 

 time and let the weights descend again, and repeated this 

 operation twenty times for each experiment. After that 

 he measured the temperature of the water, and knowing 

 the weight of water there was there, he knew the amount 

 of heat that had been generated. He also knew the 

 amount of mechanical force which had been employed 

 because these leaden weights had descended 20 feet five 

 times. He also calculated the amount of friction due to 

 the resistance pivots. Great precautions were taken to 

 prevent any error arising from the heat of the body reaching 

 the apparatus or from the heat escaping from the vessel 

 containing the water; and measurements were made to 

 find out How much heat did thus escape, and allowance 

 was made for it. Every possible correction having been 

 thus applied, Joule eventually arrived at the conclusion 

 that the mechanical equivalent of heat is 772 feet Ibs., 



D 2 



