﻿Principles of Molecular Physics. 281 



contrary, should we differ only in the question whether or net 

 luminiferous aether is condensed around a central atom (or rather 

 around the nuclei) the difference would be comparatively unim- 

 portant, as it would bear simply on a point of detail. 



Accordingly, when Professor Norton states that this last point 

 is u the only essential point of difference between us," I must 

 deny the truth of a statement which tends to shift the ground 

 of our discussion and to substitute a question of facts for a ques- 

 tion of principles. I have shown that the point touched upon 

 by the learned Professor is not the only point of difference : and 

 moreover I do not consider it an essential point in the present 

 controversy whether I can or cannot u escape the conclusion that 

 my interstitial ather, which is attracted by the central nucleus, 

 is condensed around it." Of course, I am confident that I can 

 escape the conclusion ; for I have never admitted the existence of 

 any interstitial aether between the nuclei and the envelope of a 

 molecule. But to proceed. 



I had expressed my opinion that the examples by which Pro- 

 fessor Norton illustrates his theory " do not imply the existence 

 of extended atoms or of two distinct sethereal substances." To 

 this he answers thus : 



" When he has shown this to be true of even the ordinary calorific 

 and electric phenomena, we will admit that his objection to a second 

 sethereal atmosphere interpenetrating the first may have some force." 



But this is not a sufficient reply. The onus probandi evidently 

 rests with him who makes positive assertions, not with him who 

 asks for a proof of them. Now, it is Professor Norton that 

 started his theory by positively affirming that the existence of his 

 three forms of matter was an established truth. If then we hap- 

 pen to find nothing like a sufficient ground for his affirmation, 

 it is not for us to prove that we have found no grounds ; it is for 

 him to point them out. 



He adds : 



" He has given no hint of the general manner in which he sup- 

 poses electric phenomena to be evolved. Heat he conceives to ori- 

 ginate in the vibrations of the molecules of bodies ; but it can be 

 proved, almost to a demonstration, that heat cannot originate in this 

 manner." 



Electricity is a branch of science scarcely a century old, and 

 electric theories are as yet, as everyone knows, obscure and un- 

 certain. Such being the case, I did not think it convenient to 

 devote to conjectures more or less probable space in a book of so 

 positive a character as I intended my ' Elements of Molecular 

 Mechanics ' to remain. Hence it is perfectly true that I gave 

 no hint of the evolution of electric phenomena. But the state- 





