194 W. A. Norton— Variability of the Ultimate Molecule. 
sets of waves, emanating from different virtual centers, will be 
propagated according to the law of inverse squares. 
effective action of one molecule on a contiguous one will be the 
difference between the resultant attractive action just men- 
tioned, and the opposing action of the system of repulsive 
waves first mentioned. The following is the general expression 
for this force of effective molecular action.* 
2 
f= Gea rtay e 
in which a denotes the distance between the molecular en- 
velopes, 7 the distance between the center of the system of re- 
pulsive waves first mentioned and that of the system of attrac- 
tive waves, n the coéfficient of attraction, and m that of re- 
n m ; , 
1 a and PoP this expression 
__{  k(84+2u) 1 
pulsion. If we put c=ur 
becomes 
From the point of view taken in the present discussion 
the important question here arises, whether the ultimate mole- 
cule as it has been defined, endued with the forces of external 
action just specified, is susceptible of permanent variation, and 
if so, how? It is, in fact, not difficult to see that it may be 
ulses, under 
variations of pressure. Suppose that the external pressure 1S 
increased, and the ultimate molecules are thus urged nearer to 
sive wave actions to their original value, and the mo ecules 
would return to their original relative positions ; but in fact a 
portion of this dense ether will be urged outward between the 
atoms of the envelopes, and so when the recoil comes on, the 
* See this Journal, July, 1864, p. 68, and May, 1872, p. 338. é 
+ A paper embodying the principal results obtained in the application of the 
tests here referred to, was read before the National Academy of Sciences at the 
