1833.1} Attraction and Repulsion. 453 
the same laws. And that there are numerous alternations of these 
forces. According to this law, the particles of a mass must always 
remain at some one of the intervals between attraction and repulsion. 
This may be at various distances, and thus may be explained the vari- 
ous degrees of density, which the same body may possess at different 
times. To this hypothesis it may be objected that it cannot be easily, 
admitted, of a simple force, that it should increase, as the centres of 
attraction are separated ; much less then, that this force should sud- 
denly, from a certain point, obey an opposite law, and decrease with 
_ am increase of distance. 
But to admit, in addition to this, that the same atoms, from another 
certain point, exert an opposite force of repulsion, which obeys the 
same complicated law, and that these alternations are frequently re- 
peated, until at last a regular decreasing attraction prevails, is scarcely 
possible ; since it does not accord with the extreme simplicity always 
observable in the laws of nature. 
Moreover, it is not possible by this theory alone, to account for the 
gradual increase of volume which bodies undergo, without introducing 
the repulsive agency of heat. 
Though there are, according to this theory, many points of distance 
at which particles may rest, it cannot of itself account, even for expan- 
sion, much less for liquifaction and vaporization. And again, if 
the agency of heat be added to it, on a reduction of temperature, bo- 
dies would not contract in volume, for their particles would necessarily 
be prevented from approaching, by that region of repulsion, at the li- 
mit of which they lay. This would involve the necessity of another 
extraneous agent, namely some compressing force. And thus the two 
alternate forces, assigned in the hypothesis, are ineffectual without the 
assistance of the other two, and with themare altogether useless ; con- 
sequently it is not philosophical to suppose them. 
An anonymous writer in the Encyclopedia Britanhica* treats of 
cohesion as a force, which extending to a small distance, is within 
this distance, ‘‘ little or not at all altered by slight compression, or 
expansion.” And in another place he says, “‘ it appears, that the force 
of cohesion cannot be supposed to vary much with the density, and 
it is therefore allowable to consider it as constant as far as its action 
extends.’”’ Ihave, under another head, I think proved, that this at- 
traction must not be considered, as extending only to very small dis- 
tances; and the arguments, adduced in support of this, also prove, 
that attraction is a decreasing force. These are, the increasing ratio 
* Supplement, Art. Cohesion. 
