TRANSLATORS' PREFACE. vii 



sake of a considerable class, then, we have 

 taken occasion, wherever the use of new tech- 

 nical terms or other like circumstances seemed 

 to require it, to introduce original notes and 

 commentaries, sometimes of considerable extent, 

 by the aid of which we trust the scientific prin- 

 ciples adverted to in the text will be rendered 

 easily intelligible to the general reader. 



In some few instances also we have found 

 ourselves called upon to adopt a more critical 

 tone ; where we were disposed to dissent from 

 the view taken by the author on particular 

 questions of a controversial kind, or when he 

 is arguing in support, or in refutation, of op- 

 posing theories on some points of science not 

 yet satisfactorily cleared up. 



We could have wished that our duty as 

 translators and editors had not extended be- 

 yond such mere occasional scientific or literary 

 criticism. But there unfortunately seemed to 

 be one or two points where, in pronouncing on 

 the claims of distinguished individuals, or criti- 

 cizing their inventions, a doubt could not but 

 be felt as to the perfect fairness of Arago's 

 judgment, and in which we were constrained 

 to express an unfavourable opinion on the man- 

 ner in which the relative pretensions of men of 

 the highest eminence seemed to be decided, in- 



