W. A. Norton—Theories of Heat. 191 
equivalent to saying that the atoms and molecules take up, of 
themselves, by reason of variations in their mutual actions, in 
some way induced by the impact, a series of new virtual posi- 
tions of equilibrium in the process of condensation. Again, if 
as we have seen, no portion of the energy lost in the impact is 
expended in effecting the final condensation, then it follows 
that the whole of the energy lost is consumed in the production 
of some form and amount of movement which must be, either 
actually, the heat-energy developed by the 
mterval of time that this repulsion has been in operation, mul- 
tiplied by the minute distance that these molecules have 
equal to the actual energy expended by the same repulsion in 
bringing the bodies to a se velocity. Now, if the bodies 
be serene to be perfectly elastic, this potential energy will be 
€xpended in separating fe bodies, by altering their velocities 
—the loss and gain effected being the same as has been experi- 
enced during the previous interval. The previous compression 
18 now followed by an equal recoil, and the repulsions in opera- 
tion between the contact molecules, and between all those 
which have been urged into closer proximity, pass through the 
