34 W. A. Norton on Molecular and Cosmical Physics. 
the forcible compression of the envelopes, resulting from the 
clash of the atoms; and these movements constitute also the 
living force of heat developed. 
The heat produced by extraneous pressure, or by impact, is — 
the work done by the force of pressure in compressing the — 
molecular envelopes, in opposition to the resistance of the — 
* 
the atom 
posite movements, 
i because 
