128 The Evolution of the Spheres. [March, 
evolution from original ether to motionless and dead 
worlds. 
In the case of two attracting systems approaching there 
would necessarily be a rapid augmentation of the motion of 
each. But this new motion could only be gained at the ex- 
pense of the internal temperature of the spheres (as argued 
in my article on Heat Transformations, in the “ journal of 
Science ” for June, 1880). Thus in two such systems there 
would be a rapid diminution of temperature, accompanied 
perhaps by an extreme condensation. But if they should 
come into contact with each other a result would arise simi- 
lar to that shown above in the case of two repelling spheres. 
Their sudden loss of mass motion would yield a sudden in- 
crease of heat motion, and disintegration might also, in this 
case, occur. Thus the hypothesis that force is an attribute 
of motion yields us the possibility of an infinitely aCtive 
universe, instead of a finite one, as under the hypothesis 
that force is an attribute of matter. 
Before concluding, however, a certain degree of recapitu- 
lation seems desirable. We have argued that in the con- 
ceivable original homogeneous diffusion of matter there was 
an equal balance in the directions of motion, every move- 
ment in one direction being somewhere balanced by a 
movement of equal vigour in the opposite direction. But 
however heterogeneous the state of matter in the universe, 
this condition continues necessary. For if, taking the uni- 
verse as a whole, its sum of motive energy in one general 
direction should exceed its sum of motive energy in the 
opposite general direction, the universe must move for ever 
in that direction, there being no force in existence capable 
of reversing this excess of energy. Or, if we could imagine 
the existence of space beyond the material universe, then a 
section of matter containing this excess motion might sepa- 
rate from the remaining matter, and move eternally onward, 
leaving the other section of matter in eternal rest. Such a 
condition of affairs seems inconceivable. But if there is 
not this eternal movement in one direction of the whole or 
a portion of the universe, then there must be a balance of 
its motive energies in every opposite direction. Such a 
balance, once existing, must be eternal. The universe, once 
at rest in infinite space, could never begin, of itself, to move 
through space. 
Yet the continued existence of such a balance requires 
that no particle can gain a movement in any special direc- 
tion unless some other particle gains an equal opposite 
movement. And such an exchange always occurs, whatever 
