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CHAPTER XIII. 



MISCELLANEOUS EXAMPLES OF THE EXPLANATION 

 OF LAWS OF NATURE. 



1. SOME of the most remarkable instances which 

 have occurred since the great Newtonian generaliza- 

 tion, of the explanation of laws of causation subsist- 

 ing among complex phenomena, by resolving them 

 into simpler and more general laws, are to be found 

 among the recent speculations of Liebig in organic 

 chemistry. These speculations, although they have 

 not yet been sufficiently long before the world to 

 entitle us positively to assume that no well-grounded 

 objection can be made to any part of them, afford, 

 however, so admirable an example of the spirit of the 

 Deductive Method, that I may be permitted to present 

 some specimens of them here. 



It had been observed in certain cases, that chemical 

 action is, as it were, contagious ; that is to say, a 

 substance which would not of itself yield to a parti- 

 cular chemical attraction (the force of the attraction 

 not being sufficient to overcome cohesion, or to 

 destroy some chemical combination in which the 

 substance was already held), will nevertheless do so 

 if placed in contact with some other body which is in 

 the act of yielding to the same force. Nitric acid, for 

 example, does not dissolve pure platinum, which may 

 "be boiled with this acid without being oxidized by 

 it, even when in a state of such fine division that it 

 no longer reflects light." But the same acid easily 

 dissolves silver. Now if an alloy of silver and plati- 



