﻿Principles of Molecular Physics . 433 



under a general aspect a law of action already recognized. The 

 nature of the gaseous state, on the other hand, is in no need of 

 a limit of expansion ; for if we grant, out of deference to Pro- 

 fessor Norton's opinion, that the molecules of hydrogen instead 

 of having a limit of expansion can expand indefinitely, what in 

 the world would prevent such hydrogen from being a highly 

 gaseous substance ? Surely, it would not cease to be an expan- 

 sive gas for the sole reason that its expansivity would have no 

 limit. The only reason why primitive gases have a limit of ex- 

 pansion is an a posteriori reason, viz. because they are perma- 

 nent substances, having a constitution which cannot be destroyed 

 by external action whether mechanical or chemical. Such sub- 

 stances, though expansive, must have a limit of possible dilata- 

 tion ; otherwise they would tend of themselves to their own dis- 

 solution ; in other words, they would cease to be permanent. 

 (See Molecular Mechanics, p. 145.) This is the reason why I 

 have admitted that a gas freed from all pressure would expand 

 to a determinate bulk only, and then remain at rest in the same 

 manner as if it were a liquid. Professor Norton cannot hold 

 the contrary, unless he holds either that primitive gases are not 

 permanent substances, or that their molecules, though perma- 

 nent, must repel each other at all great distances. The first 

 hypothesis would lead to the conclusion that the gaseous mole- 

 cules have no sufficient constitution of their own, but depend 

 for their existence on all sorts of exterior agencies : which view 

 is too unscientific to be adopted by the learned Professor. The 

 second hypothesis would entail the impossibility of any chemical 

 combination of gases ; for if the gaseous molecules, though per- 

 manent, repel each other at all great distances, their absolute 

 power of repelling is certainly greater than their absolute power 

 of attracting : and thus chemical affinity between two gases will 

 become an impossibility. This suffices to show that Professor 

 Norton's criticism on this first "important point" is wholly 

 without foundation. 



Heat and light. — My second "failure/' according to Pro- 

 fessor Norton's statement, regards the origin of heat and light. 

 He says : 



" Heat and light he conceives to originate in vibrations of gross 

 molecules ; but against this notion, as I shall take another occasion 

 to show, insuperable objections may be urged. If this be given up, 

 his explanation of the changes of the state of bodies must also be 

 abandoned." 



I have already stated somewhere that I conceive heat to consist 

 rather than to originate in vibrations of molecules. Of course, 

 I do not say in vibration of " gross " molecules \ because " gross 



