LIGHT. 109 



just as sound is propagated by the vibrations of wood, or as 

 waves are by water. I am not here speaking of the character 

 of the vibrations of light, sound, or water, which are doubtless 

 very different from each other, but am only comparing them 

 so far as they illustrate the propagation of force by motion in 

 the matter itself. 



I was not aware, at the time that I first adopted the 

 above, view, and brought it forward in my Lectures, that the 

 celebrated Leonard Euler had published a somewhat similar 

 theory ; and, though I suggested it without knowing that it 

 had been previously advanced, I should have hesitated in re- 

 producing it, had I not found that it was sanctioned by 

 so eminent a man as Euler, who can hardly be supposed 

 to have overlooked any irresistible argument against it the 

 more so in a matter so much controverted and discussed as 

 the undulatory theory of light was in his time. 



Although this theory has, been considered defective by a 

 philosopher of high repute, I cannot see the force of the argu- 

 ments by which it has been assailed ; and therefore, for the 

 present, though with diffidence, I adhere to it. The fact 

 itself of the correlation of the different modes of force is to my 

 mind a very cogent argument in favour of their being affec- 

 tions of the same matter ; and though electricity, magnetism, 

 and heat might be viewed as produced by undulations of the 

 same ether as that by means of which light is supposed to be 

 produced, yet this hypothesis offers greater difficulties with 

 regard to the other affections than with regard to light : many 

 of these difficulties I have already alluded to when treating of 

 electricity ; thus, conduction and non-conduction are not ex- 

 plained by it ; the transmission of electricity through long 

 wires in preference to the air which surrounds them, and 

 which must be at least equally pervaded by the ether, is irre- 

 concilable with such an hypothesis. The phenomena exhi- 

 bited by these forces afford, as I think, equally strong evidence 

 with those of light, of ordinary matter acting from particle to 

 particle, and having no action at sensible distances. I have 

 already instanced the experiments of Faraday on electrical 

 induction, showing it to be an action of contiguous particles, 

 which are strongly in favour of this view, and many experi- 



