FOOT-POUNDS TEST OF HEAT. 159 



amount of mechanical action, estimated in foot- 

 pounds. Ice may be melted by the excitation of 

 friction upon its surface ; and water may be simi- 

 larly heated by friction. In this way, Meyer, Joule, 

 and other experimenters have demonstrated that 

 the mechanical force developed by the descent of 

 a weight of seven hundred and seventy-two pounds 

 one foot, excites one degree of heat in a pound of 

 water. 



MOLECULAR VIBRATION, CONSTITUTING HEAT, CONSID- 

 ERED AS AN EQUIVALENT OF MECHANICAL ACTION 

 IN FOOT-POUNDS. 



The increase of the heat of water only one degree, 

 from 2 1 2 to 21 3, converts it into steam ; causing 

 the particles to occupy seventeen hundred fold 

 more space, against an atmospheric pressure of 

 fifteen pounds on each square inch of surface. It 

 has been ascertained also that, after the particles 

 of water are heated to 212, nine hundred and 

 sixty-seven times more heat is required to raise 

 the same water only one more degree, than will 

 raise its temperature from 39 to 40. The sur- 

 prising extent of latent vibratory action is shown 

 by multiplying 967 by 772 foot-pounds = 746,524 

 foot-pounds. The particles of steam, by the in- 

 tensity of their vibration, displace the particles 

 of the atmosphere (with its reaction of more than 

 one ton on each square foot of surface), and occupy 

 its place. 



This 967 of heat remains latent, as tested by 



