EPOCH OF DAVY AND FARADAY. 173 



guesses only when we have gained our point and 

 guessed rightly. We might personify philosophical 

 theories, and might represent them to ourselves as 

 figures, all pressing eagerly onwards in the same 

 direction, whom we have to pursue : and it is only 

 in proportion as we ourselves overtake those figures 

 in the race, and pass beyond them, that we are 

 enabled to look back upon their faces ; to discern 

 their real aspects, and to catch the true character 

 of their countenances. Except, therefore, I were of 

 opinion that the great truths which Davy brought 

 into sight have been firmly established and clearly 

 developed by Faraday, I could not pretend to give 

 the history of this striking portion of science. But 

 I trust, by the view I have to offer of these beau- 

 tiful trains of research and their result, to justify 

 the assumption on which I thus proceed. 



I must, however, state, as a further appeal to 

 the reader's indulgence, that, even if the great prin- 

 ciples of electro-chemistry have now been brought 

 out in their due form and extent, the discovery is 

 but a very few years, I might rather say a few 

 months, old ; and that this novelty adds materially 

 to the difficulty of estimating previous attempts 

 from the point of view to which we are thus led. 

 It is only slowly and by degrees that the mind 

 becomes sufficiently imbued with those new truths, 

 of which the office is, to change the face of a 

 science. We have to consider familiar appearances 

 under a new aspect ; to refer old facts to new prin- 



