578 THE PRINCIPLES OF SCIENCE. [CHAP. 



Kepler is an extraordinary instance to this effect. No 

 minor laws of nature are more firmly established than those 

 which he detected concerning the orbits and motions of 

 planetary masses, and on these empirical laws the theory 

 of gravitation was founded. Did we not learn from his 

 own Avritings the multitude of errors into which he fell, we 

 might have imagined that he had some special faculty of 

 seizing on the truth. But, as is well known, he was full of 

 chimerical notions ; his favourite and long-studied theory 

 was founded on a fanciful analogy between the planetary 

 orbits and the regular solids. His celebrated laws were the 

 outcome of a lifetime of speculation, for the most part vain 

 and groundless. We know this because he had a curious 

 pleasure in dwelling upon erroneous and futile trains of 

 reasoning, which most persons consign to oblivion. But 

 Kepler's name was destined to be immortal, on account of 

 the patience with which he submitted his hypotheses to 

 comparison with observation, the candour with which he 

 acknowledged failure after failure, and the perseverance 

 and ingenuity with which he renewed his attack upon the 

 riddles of nature. 



Next after Kepler perhaps Faraday is the physical philo- 

 sopher who has given us the best insight into the progress 

 of discovery, by recording erroneous as well as successful 

 speculations. The recorded notions, indeed, are probably 

 but a tithe of the fancies which arose in his active brain. 

 As 1* araday himself said " The world little knows how 

 many of the thoughts and theories which have passed 

 through the mind of a scientific investigator, have been 

 crushed in silence and secresy by his own severe criticism 

 and adverse examination ; that in the most successful in- 

 stances not a tenth of the suggestions, the hopes, the wishes, 

 the preliminary conclusions have been realised." 



Nevertheless, in Faraday's researches, published in the 

 Philosophical Transactions, in minor papers, in manuscript 

 note-books, or in other materials, made known in his inter- 

 esting life by Dr. Bence Jones, we find invaluable lessons 

 for the experimentalist. These writings are full of specula- 

 tions which we must not judge by the light of subsequent 

 discovery It may perhaps be said that Faraday com- 

 mitted to the printing press crude ideas which a friend 

 would have counselled him to keep back. There was 



