EPOCll OF DAVY AND FARADAY. 189 



refer conceived as measureable quantities, nor was 

 the assertion anything but a sagacious conjecture, 

 till Faraday gave the interpretation, measure, and 

 proof, of which we have spoken. The evidence of 

 the incompletness of the views of his predecessor 

 we have already adduced, in speaking of his vague 

 and inconsistent theoretical account of decomposi- 

 tion. The confirmation of Davy's discoveries by 

 Faraday is of the nature of Newton's confirmation 

 of the views of Borelli and Hooke respecting gra- 

 vity, 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 con- 

 ditions is easily illustrated in the case of Davy and 

 Faraday, both admirable and delicate 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 Mani~ 

 pulatlon, 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. 



31 Paris, i- 145. 32 Pref. p. ii. 



