234 THE PRINCIPLES OF SCIENCE. 



In the course of investigation, I have found myself 

 compelled to relinquish some preconceived notions ; but 

 I have not abandoned them hastily, nor, till after a 

 warm and obstinate defence, I was driven from every 

 post e . 



Faraday s life, again, furnishes most interesting illustra 

 tions of this tenacity of the philosophical mind. Though 

 so candid in rejecting some of his theories, there were others 

 to which he clung through everything. One of his most 

 favourite notions was finally realised in a brilliant dis 

 covery ; another remains in doubt to the present day. 



The Philosophic Character of Faraday. 



In Faraday s researches concerning the connexion of 

 magnetism and light, we find an excellent instance of the 

 pertinacity with which a favourite theory may be held 

 arid pursued, so long as the results of experiment are 

 simply nugatory and do not clearly negative the notions 

 entertained. In purely quantitative questions, as we have 

 seen, the absence of apparent effect can seldom be regarded 

 as proving the absence of all effect. Now Faraday was 

 convinced that some mutual relation must exist between 

 magnetism and light. As early as 1822 he attempted to 

 produce an effect upon a ray of polarized light, by passing 

 it through water placed between the poles of a voltaic 

 battery ; but he was obliged to record that not the slight 

 est effect was observable. During forty subsequent years 

 the subject, we are told f , rose again and again to his mind, 

 and no failure could make him relinquish his search after 

 this unknown relation. It was in the year 1845 that he 



e Experimental Inquiry into the Nature of Heat. Preface, p. xv. 

 f Bence Jones, Life of Faraday, vol. i. p. 362. 



