516 On the two great powers, [Ocr. 
last is a two-fold argument ; for since, on a small separation of the 
atoms of liquids, their attraction becomes superior to the repulsive 
force, how is it possible that without any addition to it, this repulsive 
force should expand them into gases ? And again, since the attrac- 
tion is the stronger force, when the particles are somewhat removed, 
if the two forces varied in the same ratio, it has been already shewn 
that no liquids could exist ; but atoms, so acted upon, must be reduced 
into masses absolutely dense. 
The constitution of liquids then could not be accounted for, if the 
compound repulsion of heat be supposed to vary in the same ratio as 
the attraction. 
Thirdly.—Of the constitution of gases. 
When a liquid passes into the gaseous state, its atoms are so far se- 
parated from each other that their mutual attraction is much lessened, 
but from its great augmentation of bulk, the pressure it is subjected 
to is greatly increased. Hence, in a gas the chief force opposing 
expansion, is the pressure of the air ; and to enable it to resist this force, 
the repulsion must be so augmented as to exceed the attraction by a 
force equal to the pressure. 
It is this excess of the expanding force over the attraction, which is 
alone capable of being measured. 
The experiments of Mr. Boyts, as is well known, tended to shew 
that the density of gases varies as the compressing force ; and New- 
Ton proved that if this be true, the expanding force operating between 
the atoms, will be inversely as their distances. 
But as only the excess of this force over the attraction is capable of 
measurement, it is plainly this excess of the repulsion which was 
shewn to vary inversely as the distance between atoms. 
If, then, the repulsion from heat and attraction vary in the same 
ratio, and if this ratio be the inverse square of the distance, any differ- 
ence between the two forces ought also to vary in the same ratio. 
And although this difference in the experiment of these great 
philosophers, is seen to vary in aless ratio than the inverse square of 
the distance, yet it will not appear incompatible with this or even 
some higher power being the real ratio of the repulsion between the 
atoms of any gas, when it is remembered, that on increasing or lessen- 
ing the density of a gas, by varying the compressing force ; in the 
one case much heat is given out, and in the other much is assumed. 
This must cause the expanding force apparently to vary in a far less 
inverse. ratio, than it otherwise would, if heat did not pass out on in- 
creasing, or were not assumed on lessening, the density of a gas. 
