W. A. Norton on Molecular Physics. +209 
ded as asensible indication of the extent of such changes 
of molecular condition. The mechanical work, of which the 
heat evolved serves as the measure, is expended in urging the 
On the other hand, if heat be directly applied to a body, it 
has a tendency opposite to that of a mechanical pressure, or to 
expand the molecular atmospheres, and so to reduce the inten- 
groups, and bring the mass to the condition of a homogeneous 
and symmetrical arrangement of molecules. 
pea of the molecular forces under special circumstances. 
€ general nature of these forces, and the Jaws of the variation 
of effective molecular action with the distance between two 
Seen (pp. 207, 208) that the mechanical condition of an individual 
Molecule is subject to change under the operation of heat, and 
al 
every particular substance has primarily, and inherently, its own 
special physical condition, by virtue of which it exercises an 
