FOOT-POUNDS AN EQUIVALENT OF HEAT. 4! 



chanical action requisite to produce the increase of 

 the vibrations of the electric ether pervading the 

 particles of a pound of water, to raise its heat one 

 degree of Fahrenheit's scale, has been ascertained 

 by Meyer and Joules to be the equivalent of seven 

 hundred and seventy-two foot-pounds. Instead of 

 the rotating cylinder of an electrical machine, they 

 had recourse to rotating a little paddle-wheel in a 

 box containing a pound of water at the tempera- 

 ture of thirty-nine degrees of Fahrenheit. In this 

 way, seven hundred and seventy-two foot-pounds 

 have been adopted as " the British unit-standard 

 measure of the increase of one degree of heat in 

 a pound of water;" and on this basis have been 

 made useful comparative estimates as to the eco- 

 nomical employment of fuel for developing heat 

 as motive-power. 



The vibrations of the ether pervading a bar of 

 steel by the swift rotation of a disc of sheet-iron, 

 as previously described, would probably develop 

 one degree of heat in a pound of water, by a force 

 of seven hundred and seventy-two foot-pounds, 

 were the disc made to rotate against the poles 

 of a horse-shoe magnet partially immersed in the 

 pound of water. 



In like manner, the gravitating force of seven 

 hundred and seventy-two foot-pounds may be em- 

 ployed to rotate the cylinder of an inductive elec- 

 trical machine, to test and measure the intensity of 

 both heat and light by the precise extent of action 

 employed to produce their development. 



