452 . On the two great powers, (Serr. 
of nitric acid has. Let the force of the former be 8, that of the lat- 
ter 4. If a compound atom of sulphate of potash were in this case 
exposed to three atoms of nitric acid, the potash would be separated, 
by the united action of the three atoms of nitric acid. Inthe same 
manner, the sulphuric acid may be taken from sulphate of barytes, by 
an excess of potash, as BERTHOLLET has shewn. In both the above in- 
stances, mass evidently operates*. There is also every reason for be- 
lieving, that this attraction varies as the mass, between homogeneous 
atoms, although there are not experiments proving that this is 
absolutely the case; for such experiments can hardly be expected, nor 
is it easy to propose a way of making them. . In a homogeneous solid 
mass, this law does not plainly present itself, merely from the small- 
ness of the atoms; from which, as formerly observed, the attractions ' 
of all those that are at a distance from each other (which is the case: 
with far the greater part) becomes so much less than that of contigu- 
ous particles, (on which the solidity chiefly depends,) as not to admit 
of measurement with it. 
The law of attraction which is here enforced, is also perfectly con- 
formable with the doctrine of definite proportion, and does not in fact 
at all affect it, as has been by some supposed. 
From all that has been stated, it must surely be admitted as a law 
of this power, that the attraction of atoms varies as their number. 
4thly. The ratio in which the force of attraction varies, and the 
identity of this power, with gravitation. 
I have observed, at the beginning, that the opinions of philosophers, 
upon the attraction of atoms, are various, and in many instances con- 
tradictory to each other. They are particularly so in the present ques- 
tion. 
Among other theories is that of Boscovicu, which is very generally 
known. In this it is supposed that atoms do not exert a simple 
power of attraction towards each other ; but that their mutual attrac- 
tion alternates with a mutual repulsion, not with variations of time, 
(as has been by somesupposed of the affinity of bodies for light) but with 
variations of distance. Thus that two atoms, when contiguous, repel 
each other with great force: and that this repulsion decreases with 
the increase of the distance, and at last vanishes, giving place to an 
attraction, which increases with the distance to its maximum ; whence 
it decreases, vanishes, and is replaced by the repulsion, which obeys 
* This fact does in no degree militate against the well established and important 
doctrine of definite proportions in combination. 
