301 
reside them. Its truth thus depends on these four formal 
conditions. 
First, we must know, not only that atoms exist, but all the 
laws of force which exist between them. But Mr. Brooke 
affirms (p. 31) that we know nothing of their nature, and at 
the close of his paper repeats the statement once more. And 
Mr. Spencer lays down among his first principles that matter 
is inscrutable and unknowable, and that any force of matter on 
matter at a distance is inscrutable also. If so, the conservation 
of motion, according to one view, is unthinkable and incon- 
ceivable, and according to the other, wholly unproved and 
unknown. 
Secondly, the doctrine involves the view of atoms as simply 
centres of force, not finite, impenetrable part of extension. 
And this for two reasons. Distances can only be strictly 
measured from some point, not from a bulk or space, for then 
the attraction or repulsion would have many different values 
at the same time, which is impossible. And next, these im- 
penetrable atoms, by meeting, would destroy each other’s 
motion. Hence Newton, who held this view of them, held, as 
the proper consequence, no conservation of motion, but its slow 
and ceaseless extinction. Yet Mr. Spencer sets aside the notion 
of force centres as wholly unthinkable, and Mr. Brooke includes 
it among those questions which are yet wholly unknown. Thus, 
by their own statements, a second main pillar of the doctrine 
is broken down and destroyed. 
Thirdly, the doctrine requires the admission of an ether dis- 
tinct from common matter. For if no forces exist but those 
which depend on the distance, and no kinds of substance but 
one, there can only be one single law of force, and that one is 
already known, — the law of the inverse square, or universal 
gravitation. It would follow that no repulsive force could 
exist, and no cohesion or electric action more powerful than 
gravity. The conclusion is plain. Repulsion and cohesion 
are evident facts ; and we must either reject the condition 
on which the conservation of motion depends, or accept an 
ether of some kind, distinct in its laws of force from matter. 
Now Mr. Brooke, like Mr. Grove, denies the existence of such 
an ether. He conceives that matter, immensely attenuated in 
the planetary spaces, can transmit vibrations of light, or have 
an elasticity almost a billion times greater than that of the air, 
which causes the waves of sound. The contrast of direct and 
transverse vibrations only increases this difficulty, instead of 
removing it. For direct attraction or repulsion must be more, 
not less, intense than that which is oblique and indirect. Thus, 
YOL. IX. Y 
