444 On the two great powers, {Sepr. 
The two following are proofs of attraction in liquids, and also that 
it is very considerable*. 
Sir Humpurey Davy remarks very justly, ‘‘ Cohesion is usually said 
to act only at the surface of bodies, or by their immediate contact, but 
this does not seem to be the case. It certainly acts with much great- 
er energy at small distances ; but the spherical form of minute portions 
of fluid matter can only be produced by the attraction of all the parts 
of which they are composed for each other ; and most of these attrac- 
tions must be exerted at sensible distances.” To this remark, I 
may be allowed to add, that the attraction between the particles of a 
liquid, must, moreover, be a very powerful force; for it is not only 
able to resist the force of repulsion, but also to gather the particles 
into drops against their tendency to gravitate. 
Another proof of the force of attraction in liquids, appears to me 
afforded in the fact, that the expansion of liquids increases im a great- 
er ratio than the temperature, or that liquids expand more from equal 
additions of heat at high than at low temperatures. If the pressure 
of the atmosphere were the only force opposing their expansion, li- 
quids would expand less as the temperature increased ; for, as a liquid 
expands, since it presents a greater surfacet either to the air or to 
the vessel containing it, it is pressed on with increasing force. But 
if the force opposing the expansion increases with the temperature, it 
is plain that equal additions of heat would produce less and less 
effect. | 
If these equal increments of temperature in liquids be considered to 
indicate equal additions of heat, as isthe general opinion, the only 
means by which the increased ratio of expansion can be accounted 
for, it appears tome, must be sought for in a powerful attraction 
exerted between the particles of a fluid, by the decrease of which at- 
traction, as the particles separate from each other, more effect is pro- 
duced towards enabling heat to expand the fluid, than the increase of 
atmospheric pressure produces in opposing the expansion; so that the 
sum of the powers opposing expansion is a decreasing force, and hence 
the expansion itself will have an increasing ratio. 
The nature and physical properties of gases, have especially induced 
most philosophers to consider the attraction of atoms as only acting 
* Elements of Chemical Philosophy, p. 68. 
+ This is of course the same effect ; for though a liquid expanding in a jar may 
not have the surface exposed to the air increased, yet it displaces more and more 
air, and is re-acted on by the vessel, with precisely the same force, as if it were 
compressed on all sides by the atmosphere. 
