1833. ] Attraction and Repulsion. 515 
pressure of the atmosphere. Hence it would appear, that the pressure 
of the atmosphere does not so materially affect the constitution of li- 
quids, as is generally supposed ; for, although by compressing them 
with great force, it resists their passing into vapor, yet it at the same 
time endeavours to afford them the heat requisite for this transition, 
though doubtless with less force. 
Let us now consider the constitution of a liquid, supposing the 
repulsion from heat and atttraction as varying in the same ratio. 
And first.—In a liquid, these two forces could not be equal to each 
other at any one distance of the atoms ; for since they would also be 
equal at any other, no resistance whatsoever would be offered to any force, 
such as that of the atmosphere compressing the liquid into an absolute- 
ly dense mass, the atoms of which would be in contact. They would, 
in fact, constitute, what in mechanics is named an equilibrium of in- 
difference, liable to be destroyed by the slightest extraneous force. 
Again : the attraction could not be the greater force at any one 
distance, for it would also be greater at any other; and much more 
then could no liquid exist, for there would be, besides external pres- 
sure, this additional force tending to condense the liquid, and no force 
to resist their action. 
Lastly : if the repulsive force be greater than the attraction at one 
distance, it also will at any other, and this excess of the repulsion 
over the attraction, might be sufficient to resist also the pressure of the 
air ; and the constitution of a liquid might be considered as compatible 
with such a law. But let us examine this more minutely. If the 
pressure of the air were removed from a liquid, since the repulsion was 
so far superior to the attraction, it would necessarily expand the liquid 
without limit ; for it would, at any distance of the atoms, continue the 
more powerful force. But it has, I think, been above shewn, that 
there is no evidence of liquids expanding into vapors without any ad- 
dition of heat. The vapor from a liquid in vacuo is expanded, both 
by heat assumed from the liquid and by heat forced in by the atmos- 
phere without ; and yet the evaporation of most liquids in vacuo is 
not instantaneous, as it would be according to such a law. Of some, 
as sulphuric acid and certain oils, it is at most, exceedingly slow. 
There is moreover evideuce of the attraction in liquids becoming, on 
a small separation of their atoms, stronger than the repulsion ; for 
otherwise no attraction would be apparent in them, nor would their 
atoms ever be collected into spherical drops; which can only be effect- 
ed by the excess of the attraction over the expanding force. This 
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