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at Jill 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 ' 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 



