Principles of Energetics. 63 



much heated. (4) The analogy " to the production of secondary 

 waves, when a small obstacle is encountered by primary waves, 

 propagated on the surface of water," is fallacious. Tor all such 

 obstacles are elastic, and it seems a prodigious assumption to 

 imagine that unknown inelastic, would have the same effect as 

 known elastic bodies. (5) Not only the generation of secondary 

 waves, but the origination of primary waves is experimentally 

 inconceivable. For the hypothesis is — inelastic atoms of the same 

 inertia in a uniform aether ; and the experimental condition of 

 motion is — difference of pressure. 



33. (II.) Physical phenomena are to be explained from the 

 conception of motions of different orders of molecules. 



This conception has been forced on me by the impossibility of 

 reconciling the notion of Electricity, Light, Heat, Actinism, &c. 

 as states of molecular strain or motion, with the experimental 

 facts of their coexistence, and mutual modification. 



34. (III.) Chemical phenomena are to be explained from the 

 conception of systems of different orders of molecules in dyna- 

 mical equilibrium. 



Bodies are thus conceived as systems of molecular motion ; 

 their sensible differences as dependent on differences of the 

 orders, and motions, of their constituent molecules ; their per- 

 manence as dependent on the continuance of dynamic equili- 

 brium, that is, of the same state of motion at every point ; and 

 dissolution, combination, or the formation of new bodies as the 

 result of difference between two or more systems of molecular 

 motion, in mediate or immediate contact. As an illustration of 

 this and the preceding principle, take the explanation afforded 

 of Dr. Tyndall's discovery of the greater absorption and radia- 

 tion of compound gases*. A compound gas will, in this theory, 

 be conceived as a system, the moving molecules of which are of 

 a relatively low order. Now it is clear that, suppose, for instance, 

 the molecules, whose motions determine the chemical character 

 of the gas, are, of order (1), and that the molecules, whose vibra- 

 tions give the sensation of heat, are of order (6), there are the 

 motions of five, instead of, as in a simple gas, a smaller number 

 of orders of molecules to be affected. Hence, degree of absorp- 

 tion of motion is seen to depend on the number of motions to 

 be affected. 



But I must reserve a fuller explanation of this and con- 

 nected phenomena to its proper place in the development of 

 the theory; for my object in these papers has merely been to 

 give a general introductory statement and explanation of the 

 Principles of Energetics, forming the basis of Ordinary Mecha- 



* Bakerian Lecture, 1860. 



