Oniche Materialily of Caloric. 619 
intercepted. But on the theory of capacities, 
the evaporation should proceed as rapidly at 
the close, as at the commencement, of the pros 
cess—or, in other words, evaporation should be 
wholly independent of temperature, which every 
one knows is contrary to fact. 
It may be considered, therefore, as extremely 
probable, that the tendency of ether to assume 
a gaseous form depends on its chemical affinity 
for caloric. But, (it may be asked) how is this 
affinity counteracted by an increased pressure, 
and augmented by a diminished one ? 
A circumstance, absolutely essential to the 
formation of gasses, is, that free space shall be 
allowed for their expansion.—Mechanical pres- 
sure acts as a counteracting force to this expan- 
sion; and either prevents it completely, or 
partially, according to the degree of its appli- 
cation. But from this fact, no argument can 
be drawn against the existence of chemical 
affinity, as an attribute of caloric. Two oppo- 
site forces in physics may be so balanced, that 
neither shall produce its appropriate. effect. 
Thus a body, impelled in contrary directions, 
may remain at rest, yet the operation of the 
opposing forces, in this case, cannot be denied, 
Even in chemistry, we have unequivocal ex- 
amples, in which the action of the affinities 
is suppressed by more powerful causes. Thus 
