W. A. Norton—Molecular and Cosmical Physics. 445 
and the changes which the envelopes undergo will be attended 
with a diminution of the molecular actions that are opposed 
to the force of distortion. 
Since reaching this conclusion, with regard to the physical 
cause of imperfect elasticity, and the precise molecular state of 
inelastic substances, I have met with a striking confirmation of it 
in the results of the recent experiments of Dr. Warburg on heat 
developed by sound. On referring to the table on page 444, it 
will be observed that for all substances for which the value of = 
is greater than 6°9 (that is, for all the harder and more ten- 
acious substances), the maximum attraction between their mo- 
lecular envelopes occurs at distances greater than that of quies- 
ence, Oa, and that in consequence the diminution of this attrac- 
tion will be greater for small diminutions of the distance between 
the molecules than the increase of the same for small incre- 
ments of the distance. Now a diminution of this attraction 
will be attended with a contraction of the molecular envelopes 
and a consequent evolution of heat, while an augmentation of 
the attraction will be attended with an expansion of the enve- 
lopes and a consequent absorption of heat-pulses from without. 
permanent contraction of the molecular envelopes, and therefore 
4 certain amount of heat given out. The gradual subsidence 
of the vibrations, after the inciting cause has ceased to act, 
results from the process of contraction of the envelopes, attend- 
ant upon each vibration, and the consequent evolution of heat- 
energy. 
Tndia-rubber must belong to that class of substances for 
which the ratio = is less than 6-9, for the heat given out by it 
when it is stretched, shows that its envelopes must contract 
when the molecules recede from each other (p. 443). Still as 
much below 6-9. Again, the fact that heat pee oa ag 
ia- 
are 
sibi 
lopes contract, and their attractive action diminishes in conse- 
