190 W. A. Norton—Theories of Heat. 
differing positions of equilibrium, and these diverse positions 
cannot be taken up if the forces exerted remain the same at the 
same distance. We are, therefore, compelled to abandon one 
prominent feature of the doctrine of atomic heat-vibrations, and 
admit that the mutual actions of atums are liable to change, un 
the influence of applied forces, by reason of some change taking 
plice in the physical and internal mechanical condition of the atoms 
themselves. 
We may conclude, therefore, that when two bodies collide, 
the condensation that subsists at the close of the impact is, in 
all probability, due to some action, exerted by the force devel- 
oped in the collision, upon the ultimate atoms of the bodies, 
which has the effect to change the physical and internal 
mechanical condition of each atom—a result which is conceiv- 
decreases to zero at the instant of the final separation of the 
bodies. It is this force of mutual repulsion, developed at the 
*The mutual repulsion between the molecules in the interior of the two bodies 
comes into operation, it is true; but it is only incidentally, as an anta c wie 
to oe condensation which the repulsion develo between the contact-molec _ 
to p e 
amount of the condensation experienced by the bodies, and the duration of ns 
con ill vary with the intensity of the internal elastic resistance thus calle 
into play, for a given displacement of the molecules: or, in other words, with ee 
coefficient of elasticity. They should also vary with any deviations from perfect 
elasticity that may subsist. 
