9$ DEFINITION OF GASEOUS HYPOTHESIS. 



" Admitting the correctness of the equivalent I have 

 named, it is obvious that the vis viva" (the first time Joule has 

 used this expression in connection with his own experi- 

 ments) " of the particles of a pound of water at (say) 

 51 , is equal to the vis viva in a pound of water at 50, 

 plus the vis viva that would be acquired by a weight of 

 8171b. after falling through the perpendicular height of one 

 foot." Even now he does not use vis viva according to its 

 mathematical definition, but as half the quantity. 



" Assuming," he continues, "that the expansion of elastic 

 fluids is owing to the centrifugal force of revolving atmo- 

 spheres of electricity we can easily estimate the absolute 

 quantities of heat in matter. For in an elastic fluid the 

 pressures will be proportional to the square of the velocity 

 of the revolving atmospheres, and the vis viva of the atmo- 

 spheres will also be proportional to the square of the velocity. 

 Consequently the pressure will be proportional to the vis 

 viva. Now the ratio of the pressure of the elastic fluids 

 at temperatures 32 and 33 is 480-^481, consequently the 

 zero of temperature must be at 480 below the freezing point 

 of water. We see then what an enormous quantity of vis 

 viva exists in matter. A single pound of water at 6o° must 

 possess 480 + 28 = 508° of heat, or, in other words, it must 

 possess a vis viva equal to that acquired by a weight of 

 4i5,0361bs. after falling one foot. The velocity with which 

 the atmosphere of electricity must revolve in order to present 

 this enormous amount of vis viva must of course be pro- 

 digious, and equal probably to the velocity of light in the 

 planetary space, or to that of an electric discharge, as 

 determined by the experiments of Wheatstone." 



This account of the application of his theory, which is 

 expressed in strict accordance with dynamical principles, 



