i8 7 8.] 
Past Changes in the Universe. 
369 
It may be remarked that the conditions above arrived at, 
as a basis for recurring changes in the Universe, were not 
deduced solely with this object in view ; but these very con- 
ditions follow independently as necessary consequences of 
the explanation of gravitation afforded by the kinetic theory, 
so that it becomes a remarkable fadl that the very conditions 
that follow on the explanation of gravitation are precisely 
of that character required to account for recurring changes 
in the Universe. The more the subject is reflected on, the 
more apparent will it become that in broad principle other 
conditions for producing recurring changes are not conceiv- 
able — keeping in view the necessity (in order to effedl recur- 
rence) that the cooled down material of the Universe should 
be that material which is utilised for the development of 
fresh centres of heat ; and there would appear to be a 
simple grandeur (not out of harmony with the recognised 
characteristics of Nature) in this great result being brought 
about by the mere movement of the stars according to the 
kinetic theory. Also there would be a sort of harmony or 
(as is known) tends to establish itself between the energy of the translatory 
motion of the molecules as wholes, and the energy of the motion of their 
parts (internal motions). Thus the throwing of the parts of molecules into 
motion (from any cause) would tend to produce motion in the molecules as 
wholes. In principle, therefore, the development of motion in the smaller 
parts of matter tends to produce translatory motion in the larger parts (and 
that whatever the relative scale may be). This might possibly have its appli- 
cation as an auxiliary cause for the development of translatory motion in the 
larger scale parts of matter (represented by the stellar masses), through the 
intermediary oi the smaller parts (molecules), and the minute moving particles 
of the medium in which these smaller parts are immersed. 
Another point may perhaps be worth noticing here. When the molecules 
of a compound gas (immersed in another gas) break up from any cause into 
their components, each of these smaller components tends to acquire from 
the rest of the gas the same absolute kinetic energy of translatory motion as 
the entire compound molecule possessed (before it was broken up) ; so that 
therefore the total energy of a given portion of gas may be suddenly greatly 
augmented by the mere breaking up of its (compound) molecules into parts. 
If we imagine any limited portion of a gas to be immersed in another gas of 
unlimited extent (or if the portion of gas be supposed enclosed in some way 
so as to permit expansion, and at the same time to allow a free exchange of 
energy between it and the other gas), then a change in the state of aggre- 
gation — by the breaking up into parts of the compound molecules of the en- 
closed gas — will be followed by a considerable transference of energy from 
the outer gas to the enclosed gas; for when equilibrium is again attained, 
each of the small parts into which the compound molecules of the enclosed 
gas are split up will have acquired from the outer gas the same absolute kinetic 
energy of translatory motion as the entire molecule possessed before it was 
broken up. Thus the mere adt of breaking up (disintegration) of matter, 
immersed in a medium enclosing a stove of motion , may cause considerable 
transference of energy from this medium to the immersed matter, tending to 
produce expansion and rebound. Possibly this principle might also have 
some bearing on the disintegrating changes continually taking place in the 
Universe. 
VOL. VIII. (N.S.) 2 B 
