1833.] Aitraction and Repulsion. 451 
all particles must be supposed to attract each other. Since then in 
liquids and solids also an attraction is always manifest, it follows that 
between homogeneous atoms this force is universal. We have equal 
reason to admit its action between all heterogeneous atoms, though it 
has until lately been considered to exist only between a limited variety. 
The fact that many atoms refuse to combine may be readily explain- 
ed, as Dr. Murray has observed, by taking all the forces that oppose 
combination into consideration. These forces may in many instances 
be superior to that of the attraction, and then the latter will apparent- 
ly not exist. A very strong proof of the universal action of attraction 
between dissimilar atoms, and even when in the gaseous state, is af- 
forded by the fact that all gases without any exception will either 
combine, or else mix, when brought together ; and further that all dis- 
solve water when placed over it*. 
The reason of an attraction being universally apparent between all 
gases, though not between all liquids and solids, is readily explained. 
In the former state, the particles of the body are not detained by any 
cohesion, but exert an effective repulsiont for each other, which ren- 
ders them easy to be put into motion ; hence even a weak attraction 
exerted by another gas becomes evident. On the other hand, the par- 
ticles of solids and of liquids, on a small separation from each other, 
are detained by their cohesion, it being stronger than the attraction 
of many bodies for them. 
With respect to the attraction, which acts between atoms, I trust 
that under the present head sufficient has been shewn, to justify its 
being considered as a power, which is universal, i. e. which is exerted 
(though with various degrees of force) between all particles similar 
and dissimilar. 
3dly. The effect of mass on contiguous attraction. 
If the statements, laid down in the two former heads, be true, it fol- 
lows of necessity, that attraction must also vary with the mass, or 
number of attracting atoms ; and this is confirmed by experiment, with 
respect to heterogeneous atoms. Thus it is well known, that a particle 
of sulphuric acid has a stronger attraction for one of potash than one 
*Itis well known Mr. Daron and others have endeavoured to explain these 
facts, without the assistance of an attraction. This will be discussed in a future part 
of this paper. 
+ Lhave used the term effective, here and elsewhere, to denote the excess of 
one force above its opponent ; thus, if the attraction be 4 but the repulsion 10, 
the effective repulsion = 6. In like manner, there is in some cases an “ effective” 
attraction. 
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