vi INTRODUCTION 



The task is one worthy of the powers of a great investigator, 

 for he who has himself made bold advances into the unknown 

 can best appreciate the difficulty of breaking away from 

 accepted ideas, the labour required to bring precision into 

 a field where nothing but vague general ideas prevail, the 

 independence of judgment necessary in making a decision 

 as to which facts are of fundamental bearing, which trivial. 

 Only too often the student who has just taken his degree finds 

 nothing remarkable in the enunciation of the laws of motion 

 or the discovery of electromagnetic induction, ideas which 

 are made so familiar to him that they seem obvious, and the 

 true significance of which escapes him. He reads of the 

 apparently simple experiments of a Rutherford or a Lenard, 

 and feels that he could have made them himself, knowing 

 nothing of the opinions prevailing and the apparatus avail- 

 able at the time, and knowing, indeed, very little about real 

 efi^ort of any kind. On the other hand the great investigator 

 knows from experience the difficulty of formulating the prob- 

 lem in a precise form: the hold which old and established 

 methods of thought retain: the risk of sailing in uncharted 

 seas. It is from him that we can expect a just appreciation 

 of the outstanding individual achievements of science, and 

 a sure detection and appraisal of true originality of outlook. 

 A Clerk Maxwell can best judge the greatness of a Cavendish. 

 In these studies of great men by Professor Lenard the 

 reader will find a vivid sympathy, a generous enthusiasm 

 and an illuminating criticism which brings out in lively 

 fashion both the personality and the secret of the scientific 

 greatness of the subject - let the life of Faraday serve as an 

 example. The great men stand as living figures, belonging 

 to their times, yet in many ways strangely sympathetic to 

 ours. The author has brilliantly succeeded in presenting 

 his subjects as individual men, of widely different disposi- 

 tions, beset with the most diverse circumstances, and 

 yet showing how all these individuals are made kin by 



