TRANSLATORS’ PREFACE. Vil 
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- 
