EPOCH OF DAVY AND FARADAY. 301 



sistent theoretical account of decomposition. The confirmation of 

 Davy's discoveries by Faraday is of the nature of Newton's confirma- 

 tion of the views of Borelli and Hooke respecting gravity, or like 

 Young's confirmation of the undulatory theory of Huyghens. 



We must not omit to repeat here the moral which we wish to draw 

 from all great discoveries, that they depend upon the combination of 

 exact facts with clear ideas. The former of these conditions is easily 

 illustrated in the case of Davy and Faraday, both admirable and deli- 

 cate experimenters. Davy's rapidity and resource in experimenting 

 were extraordinary, 31 and extreme elegance and ingenuity distinguish 

 almost every process of Faraday. He had published, in 1829, a work 

 on Chemical Manipulation, in which directions are given for perform- 

 ing in the neatest manner all chemical processes. Manipulation, as he 

 there truly says, is to the chemist like the external senses to the 

 mind ; 32 and without the supply of fit materials which such senses only 

 can give, the mind can acquire no real knowledge. 



But still the operations of the mind as well as the information of the 

 senses, ideas as well as facts, are requisite for the attainment of any 

 knowledge ; and all great steps in science require a peculiar distinct- 

 ness and vividness of thought in the discoverer. This it is difficult to 

 exemplify in any better way than by the discoveries themselves. Both 

 Davy and Faraday possessed this vividness of mind ; and it was a con- 

 sequence of this endowment, that Davy's lecture upon chemistry, and 

 Faraday's upon almost any subject of physical philosophy, were of the 

 most brilliant and captivating character. In discovering the nature of 

 voltaic action, the essential intellectual requisite was to have a distinct 

 conception of that which Faraday expressed by the remarkable 

 phrase, 33 " an axis of power having equal and opposite forces :" and the 

 distinctness of this idea in Faraday's mind shines forth in every part 

 of his writings. Thus he says, the force which determines the decom- 

 position of a body is in the body, not in the poles. 34 But for the 

 most part he can of course only convey this fundamental idea by illus- 

 trations. Thus 35 he represents the voltaic circuit by a double circle, 

 studded with the elements of the circuit, and shows how the ariions 

 travel round it in one direction, and the cath'ions in the opposite. He 

 considers 38 the powers at the two places of action as balancing against 

 each other throuo-h the medium of the conductors, in a manner analo- 



O ' 



31 Paris, i. 145. 32 Pref. p. ii. 3S Art. 517. 



14 Art. 661. 35 96 S6 917. 



