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CHAPTER XVII. 

 The Ether. 



IN what has just been said, we have spoken of 

 light, only with respect to its power of illuminating 

 objects, and conveying the impression of them to 

 the eye. It possesses, however, beyond all doubt, 

 many other qualities. Light is intimately con- 

 nected with heat, as we see in the case of the 

 sun and of flame ; yet it is clear that light and 

 heat are not identical. Light is evidently con- 

 nected too with electricity and galvanism ; and 

 perhaps through these, with magnetism : it is, as 

 has already been mentioned, indispensably ne- 

 cessary to the healthy discharge of the functions 

 of vegetable life ; without it plants cannot duly 

 exercise their vital powers : it manifests also 

 chemical action in various ways. 



The luminiferous ether then, if we so call the 

 medium in which light is propagated, must 

 possess many other properties besides those 

 mechanical ones on which the illuminating 

 power depends. It must not be merely like a 

 fluid poured into the vacant spaces and inter- 

 stices of the material world, and exercising no 

 action on objects ; it must affect the physical, 

 chemical and vital powers of what it touches. It 



