W. A. Norton—Theories of Heat. 193 
tions,* that in the case of inelastic bodies the approximation 
that, as the condensation goes on, a series of instantaneous 
positions of equilibrium of the atoms and molecules (so far as 
the natural molecular actions are concerned) are passed through, 
by reason of the change just noticed, induced in the condition 
of the atoms. The potential repulsive energy subsisting at 
the point of contact, is thus mainly expended in disturbing the 
equilibrium of the atomic envelopes. The heat-energy evolved 
consists in the return of these envelopes to their former undisturbed 
condition, with attendant vibratory movements of their different 
layers, and the ethereal waves resulting therefrom. As the atomic 
envelopes return to their original condition, with the evolution 
of heat, the condensation or set, subsisting at the instant of the 
complete separation of the bodies, will pass off, in consequence, 
more or less. Any permanent set that may remain after the 
dies have recovered their original temperature, being chiefly 
due to changes in the atomic forces, resulting from alterations 
of the physical condition of the atoms incidental to the act of 
compression, will not have been attended with the expenditure 
of any considerable portion of the energy, or living force, that 
is lost in the impact. 
_ The theory may be succinctly stated as follows: The destruc- 
tion of the motion of approximation of the two bodies, during 
* This Journal, June, 1872, p. 444. 
+ This Journal, June, 1872, p. 443 and 444. 
