﻿Principles of Molecular Physics. 435 



Transmission of rays. — My critic says : 



" The doctrine that transparent bodies transmit rays of light by 

 the motion of their own molecules, will hardly be accepted, we 

 think, by physicists. " 



The author knows, I assume, that Mr. Grove, who is an eminent 

 physicist, holds in his ' Correlation of Physical Forces ; that the 

 phenomena of light can be explained without any intervention of 

 aether, and consequently by the vibratory motion of ponderable 

 matter. And although I think, as I have remarked in my 

 6 Molecular Mechanics/ that Mr. Grove has failed to establish 

 the non-existence of aether as a special substance, his arguments 

 have still sufficient weight in the case of the transmission of 

 li°;ht through solid bodies, as the reader will see in my treatise 

 (pp. 190-192). 



The author adds that it would be " a waste of time " to argue 

 against this view. I cannot subscribe to his opinion, nor pro- 

 bably would Mr. Grove. A view unsupported by reasons may 

 be passed over without arguing, as it might be a waste of time 

 even to mention it : but when reasons are adduced, a critic 

 should at any rate mention the fact of their existence and bear- 

 ing, before he decides that arguing against them is a waste of 

 time : a decision which should rather be left to the reader him- 

 self. The principal reason adduced by me in support of my 

 view was that "in the hypothesis that the ray is transmitted by 

 the motion of the aether intercepted between the molecules, the 

 regular arrangement of these would not explain the fact of the 

 transmission of a ray in any other direction than that deter- 

 mined by molecular interstices in a straight line. Now the ray 

 is in fact transmitted in all other directions. Accordingly we 

 maintain that the transparent bodies transmit the rays of light 

 by the motion of their own molecules, not by the motion of in- 

 tercepted aether" (Molecular Mechanics, p. 191). Had Pro- 

 fessor Norton transcribed this argument, and then declared his 

 repugnance " to waste time " about it, the reader would have 

 been able to judge of the matter : but my opponent did not give 

 the reader any such satisfaction, although, I venture to say, this 

 would not have been a waste of time. 



Professor Norton adds : 



" The notion that a certain substance radiates light of a certain 

 colour, because its molecules are made to vibrate in unison with the 

 ray of that colour, will not stand ; for the results of spectral analy- 

 sis show that the parts of a body which are capable by vibration of 

 giving out any colour are precisely those which absorb and stifle that 

 colour. This fact, we may add, also proves conclusively that the 

 rays cannot be transmitted by the motion of the molecules." 



