532. On the two great powers, [Ocr. 
heat grow less, (i. e. it falls in temperature,) and hence it rapidly re- 
ceives heat forced into it from the vessel and external air. The truth 
of this is evident from the fact, that, during the experiment, the rare- 
fied air at first falls in temperature, but afterwards rises to the same 
temperature as the external air; and if the exhaustion be again con- 
tinued, the air again expands, falls in temperature, and therefore again 
receives heat; and, as long as heat is forced into it, so long must it 
expand, and the point of stable equilibrium be removed toa greater 
distance. Were it possible to procure a receiver impermeable by heat, 
there is every reason to believe, that the expansion of the contained air 
would terminate after several increments of volume ; for it cannot be 
supposed, that, on the removal of pressure, a gaseous fluid would expand 
without limit, unless the repulsive force, operating between its atoms, 
be considered to vary either in the same or in a less inverse ratio 
of the distance, than their attraction ; and since it has been already 
shewn, that either of these cannot be a law of the repulsion in bodies, 
in any degree of combination, or inany other state, analogy will show, 
that neither of them can be a law of the repulsion of atoms in the 
gaseous state. 
Another objection which may be presented, is, the apparent fact, that 
the effective repulsion in gases, varies inversely as the distance of the 
atoms ; for, according to the doctrine which I have laid down, since the 
actual repulsive force is considered as varying in a higher inverse ratio 
of the distance than the attraction, and since the attraction is supposed to 
vary as the inverse square of the distance, the effective* repulsion ought 
to vary ina higher inverse ratio of the distance than the inverse square ; 
and not therefore only inversely as the distance, as it appears to do. To 
this I may answer, that, as I have before remarked, an ingress of heat 
takes place, on removing pressure from the air, and an egress on increasing 
the compressing force. This reception of heat on the one hand, and loss 
_ of heat on the other, must cause the effective repulsion apparently to 
vary in a much lower inverse ratio of the distance, than it would, did 
the air always possess the same quantity of heat ; and from this cause 
Mr. Boyun’s experiments, and the doctrine I have laid down, contain 
nothing contradictory. 
In like manner, in the case of a body gravitating towards a planet, 
the force varies inversely as the square of the distance from the cen- 
tre. But, by varying the quantity of matter in the planet, in some 
* The excess of the repulsion, over the attraction ; the only force which, in a 
gaseous fluid, admits of measurement. 
