ioo Traces of Unity in the Various 



de-materialize the notion of light. The case of light, 

 indeed, does not seem to differ much from that of heat. 

 Nay it does not follow that the passage of light through 

 extra-mundane space can be appealed to as a proof that 

 light is something independent of matter. For who can 

 say that such space is a vacuum in the strict sense of 

 the word ? Matter, there is every reason to believe, is 

 diffusible to a degree which passes conception, and the 

 best vacuum is only a plenum from which some, perhaps 

 not very many, of the more solid particles have been 

 taken. The Torricellian vacuum over the column of 

 mercury in the tube of the barometer is not devoid of 

 mercury : and it is difficult to regard the case of this 

 vacuum as in any way peculiar in its relation to a plenum. 

 Indeed, until it is possible to assign limits to the diffus- 

 ibility of matter.it seems necessary to believe that cos- 

 mical space is not matterless even when most empty of 

 matter that in this very place, with sufficiently delicate 

 tests, might be detected unequivocal traces of every 

 material body in the universe, planet, or sun, or star, 

 great and small, one and all. Nor does the extreme 

 velocity of light present any valid objections to this 

 notion. For, as is shewn by the rate at which electri- 

 city traverses a metal wire a case where each 

 particle of matter is undoubtedly affected electricity 

 can travel with equal or even greater velocity ; and not 

 only so, but as is proved by Mr. Latimer Clarke in 

 some experiments when the wire used was 760 miles in 

 length electricity agrees with light and also with 

 sound, in travelling (provided the effects of lateral 

 induction be the same) at the same rate of velocity 

 whatever be its intensity. Indeed, for anything that 

 appears to the contrary, light may be a mode of motion 

 in ordinary matter, which has nothing to do with any- 



