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at all times and in all circumstances, in fact, exists.” Having 
once assumed that motion never commences, another assump- 
tion naturally follows, i.e., that motion never ceases. It may 
be lost to perception or measurement, may wholly change its 
modes, pass away from the earth altogether, but through space 
it will act for ever. Mr. Grove, in reference to this subject 
says, — “ The term c perpetual motion/ which I have not unfre- 
quently employed in these pages, is itself equivocal. If the doc- 
trines here advanced be well-founded, all motion is, in one sense, 
perpetual. In masses whose motion is stopped by mutual con- 
cussion, heat or motion of the particles is generated ; and thus 
the motion continues, so that if we could venture to extend 
such thoughts to the universe, we should assume the same 
amount of motion affecting the same amount of matter for 
ever.” There is no evidence possible that will justify us in 
extending such thoughts to the universe, and the assumption 
might be at once discarded. Perpetual motion we believe to 
be as baseless in a cosmical, as it is in a mechanical sense. 
The reason, however, why it is so tenaciously maintained is 
clearly stated by Mr. Spencer, and is seen to be not for the 
sake of the hypothesis in itself, but because it helps to support 
the theory of evolution. His words are , — “ The continuity of 
motion, like the indestructibility of matter, is clearly an axiom 
underlying the very possibility of a rational theory of evolution. 
That kind of change in the arrangement of parts, which we 
have found to constitute evolution, could not be deductively 
explained, were it possible for motion either to appear or to 
disappear.” It has already been shown that it is possible for 
motion to appear ; we have now also to show that it is possible 
for it to disappear. Allowing for the moment that it cannot 
disappear, or rather cannot cease to be, on earth, can it pass 
beyond earth’s limits and exist in space ? This is possible, if 
space be occupied by matter, but it is not possible if space be 
a void. It is not needful for our present purpose to enter into 
any metaphysical subtleties regarding the nature of space, but 
only to ascertain as far as possible whether it be filled with 
matter, in however attenuated a form, or not. 
27. That it is so occupied is asserted in the plainest terms 
by Professor Tyndall, and the properties of the universal 
substance stated. Of it he says, with, apparently, every 
confidence that he is describing something having a real, and 
not merely an assumed existence, “ The luminiferous ether 
fills stellar space ; it makes the universe a whole, and renders 
the intercommunication of light and energy between star and 
star possible. But the subtle substance penetrates farther : it 
surrounds the very atoms of solid and liquid substances.” All 
