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. 



&quot;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- 



