113 



bodies can receive, according to the Professor's notion, motion 

 from this ether, and communicate motion to it. Ether, there- 

 fore, he affirms to be a material substance, less dense than that 

 with which we are usually familiar, and capable of assuming the 

 modes of motion called heat, light, electricity, and magnetism. 

 All this sounds as dogaiatic and assured as though it were a 

 well-ascertained fact, instead of being an effort of the scientific 

 imagination, to add a necessary supplement to a favourite 

 theory. 



28. We find Mr. Grove decidedly dissenting from it, because he 

 believes it an inadequate explanation of the phenomena it was 

 invented to explain. He thinks light, for instance, results 

 from a vibration or motion of the molecules of matter itself, 

 rather than from a specific ether pervading it.'' And as 

 regards heat, he says, — "That the phenomena presented 

 by heat, viewed according to the dynamic theory, cannot 

 be explained by the motion of an imponderable ether'' (p. 167). 

 Again, he writes (p. 168), " An objection that immediately 

 occurs to the mind in reference to the ethereal hypothesis of 

 light is, that the most porous bodies are opaque ; cork, charcoal, 

 pumice-stone, all very porous and very lights are all opaque." 

 The natural objection to Mr. Grove's theory is, that if these 

 forces be the result of molecular action, the space between the 

 sun and earth must be a plenum, filled with matter. This he 

 supposes it to be, the matter consisting of the atmospheres of 

 the planets, very much attenuated, but sufficiently dense to 

 transmit these molecular movements. But even this he 

 acknowledges to be an assumption, in more modest and 

 philosophic words than those used by Professor Tyndall. He 

 says, — At the utmost, our assumption, on the one hand, is, 

 that wherever light, heat, &c., exist, ordinary matter exists, 

 though it may be so attenuated that we cannot recognize it by 

 the tests of other forces, such as gravitation ; and that to 

 expansibility of matter no limit can be assigned. On the 

 other hand, a specific matter without weight must be assumed, 

 of the existence of which there is no evidence, but in the 

 phenomena, for the explanation of which its existence is 

 supposed. To account for the phenomena, the ether is 

 assumed ; and, to prove the existence of the ether, the 

 phenomena are cited. For these reasons, and others above 

 given, I think that the assumption of the universality of 

 ordinary matter is the least gratuitous." Each is, therefore, 

 an assumption, and a gratuitous one, but that of the ether the 

 most so ; and on this most gratuitous assumption the notion of 

 the continuity of motion and the persistence of energy is based. 



29. But Mr. Grove is not by any means alone in his objec- 



