﻿Principles of Molecular Physics. 437 



colour that falls upon them, and take up its vis viva, is it neces- 

 sary to conclude that the ray will be " transformed into a mole- 

 cular electric current ? " or is it not more natural to maintain 

 that the ray will remain a ray and undergo no transformation 

 at all ? A transformation must have a cause calculated to sub- 

 stitute one form for another, and therefore to destroy the form 

 of the ray and to introduce the form of an electric current. 

 Now the cause which destroys a kind of motion must be con- 

 trary to that kind of motion : if it were in unison with it, it 

 would propagate instead of destroying it. And therefore, if 

 the atoms of the electric atmospheres vibrate in unison with 

 the ray, we must conclude that the ray is transmitted or pro- 

 pagated, not transformed into a molecular electric current. 

 But to proceed. 



Elements and molecules. — Professor Norton allows that my 

 leading principles " may in the main be conceded :" a conces- 

 sion for which I feel obliged; but then he thinks that such 

 principles " by no means cover the whole ground upon which 

 the theory is raised/'' The thing is quite possible, as my ( Mo- 

 lecular Mechanics ' contains suggestions and hints which are 

 not strictly and solely derived from such " leading " principles ; 

 yet they are few in number, and of so secondary an importance 

 that I do not consider them as a substantial part of the theory*. 

 But even so, those suggestions are not gratuitous, and cannot 

 be discarded without a fair examination of the reasons by which 

 they are supported. 



Professor Norton to prove his assertion points out that I as- 

 sume " that all elements or material points of the same form of 

 matter act, under similar circumstances, with the same inten- 

 sity." I wonder how this can be true, since in my book I ex- 

 plicitly stated the contrary. I said : " One might ask : Is there 

 any material element possessing a greater power than any other? 

 This question cannot be answered in the present state of science. 

 Still it would be rashness on our part to assume, without neces- 

 sity or indication of any kind, that all elements have equal 

 power" (Molecular Mechanics, p. 69). It is strange that my 

 American critic should have read the opposite, especially when 

 we consider that all the molecular formulas contained in the 

 book take into account the different intensity with which ele- 

 ments can act under the same circumstances. The allegation is 

 therefore a clear mistake. 



Then my critic argues in the following strain : 



* I take this opportunity to acknowledge the impropriety of an example 

 given in my hook (p. 171), where I stated that the sun exercises no sen- 

 sible influence in the production of tides. Professor Haughton of Trinity 

 College, Dublin, kindly pointed out the inaccuracy of the statement. 



Phil. Mag. S. 4. Vol. 37. No. 251. June 1869. 2 G 



