188 W. A. Norton—Theories of Heat. 
In the propagation, then, of sound, or a force of percussion, 
through a solid or liquid, the force of repulsion develope 
between the contiguous atoms of two molecules should be as 
great as would be developed between the constituent atoms of 
the molecules by an equal relative displacement. The velocity 
imparted by this repulsion to the molecule, would of course be 
less than that communicated to the single atom by an equal 
force; but less only in the ratio of the number of atoms in the 
molecule to unity. Unless, then, the integrant molecules of an 
elastic solid, or of a liquid, contain a large number of atoms. 
the velocity of propagation through it of sound, or a force of 
percussion, should not be many times less than that which 
should oceur from atom to atom of each of its molecules, under 
ds. 
ertain phenomena attendant upon the development of heat by 
impact, are opposed to the hypothesis of atomic heat-vibrations. it 
contiguous molecules; the repulsive forces exerted by 1, if 
experiencing any change, certainly not being proportionally 
increased. The constituent atoms of each molecule must then, 
if invariable as supposed, have taken up 
equilibrium, in which the attractive actions exerted by them 
upon the atoms of a contiguous molecule have augmented. 
Hence the actions of the constituent atoms of each molecule 
on one another must have changed. Now such a change 12 
the intensities of the atomic forces that take effect at a give? 
distance, cannot result from the mere fact of atomie vibrations. 
Again if we reflect that the compression existing at the moment of 
the separation of the two colliding bodies, which serves as the meas 
