186 W. A. Norton — Variability of the Ultimate Molecule. 
arov to $s. ‘To suppose that these molecules, during all the 
progressive permanent changes of mutual distance, continu 
to exert forces of mutual action varying only with the distan 
is to suppose that they were capable of taking, under the o 
ration of such forces, constant at the same distance, an ind 
nite series of positions of equilibrium differing from each other 
. 
experience a sensible permanent change of mec 
