456 On the two great powers, (Serr. 
~attraction. And, since it operates between the liquid and gaseous 
atoms, most of which are at a much greater distance from each other, 
than any two neighbouring atoms of the vapor, it at once proves that 
atoms in a gaseous state attract each other at all distances. 
Part IIl.—Of Repulsion. Div. 1st. 
Were the attractive force, which we have hitherto treated of, op- 
posed by no other power, it is manifest, that the atoms of all bodies 
would be in perfect contact, and that all masses would be absolutely 
dense. Hence there must of necessity exist some divellent, or repul- 
sive power in bodies; for the atoms of none can be in contact, since 
all are capable of contracting from certain causes. As they, in con- 
tracting, occupy a less space than before, the differenee between their 
present and former bulks must have intervened between their atoms; 
and even much more; for no limit has been found to the contraction of 
bodies. It is owing to the same divellent power, that heterogeneous 
atoms cannot come into contact. Hence the limited number of com- 
binations ; and hence it happens, that most gases, on being presented 
to each other, merely mix, and cannot enter into combination. 
Since a divellent or repulsive force is always as evidently operating 
to prevent the contact of atoms, as an attraction, exerted by them, is 
operating to favor their contact, the former has no less commanded 
the attention of philosophers, than the latter. 
Any theory, which would at all admit of investigation, must suppose 
the great opponent force to the attraction of atoms to depend, either 
ona repulsive power inherent in and exerted by them; or on this 
force, aided by the power heat ;—or on the power heat alone. 
These I shall attempt to investigate severally.—First. Whether the 
opponent force to the attraction of atoms is a power inherent in and 
exerted by them. 
The theory of Boscovicn and a few others may be placed under this 
head. His theory, as above observed, would sufficiently account for 
the constitution of bodies, if their volumes were permanent, and their 
particles always at rest. But, since all bodies are capable of possess- 
ing every degree of density, and of expanding and contracting gradu- 
ally, such a theory would interfere with known phenomena, which 
could not take place on the admission of it. 
Bodies, as I have before remarked, would never expand without the 
introduction of some extraneous expanding power, nor could they con- 
tract, without the admission of a compressing force, of which we have 
no evidence, and the action of which could not be explained. 
