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POPULAR SCIENCE REVIEW. 
Pingincula, which are of extreme value, but we must now conclude our very 
Imperfect notice of this Mr. Darwin’s latest labour ; and while we thank him 
most heartily tor giving us so admirable a book, we confess that he has but 
opened up a vast field wherein future naturalists may reap rich harvests of 
experiment and observation. 
TYNDALL ON LIGHT AND SOUND.* 
T WO new editions of these splendid though in a certain sense elementary 
volumes are now before us, and demand a word or two in notice of 
their author’s efforts at improvement of his former labours. The book on 
(l Light ” is of course very much as it was in the first edition, because in the 
department of Physics, to which it belongs, there has not been very much 
done to advance the science. Still, however, it has certain features of 
novelty. For example, there is the Appendix, in which are to be found 
three brief addresses by distinguished Americans, which, though short, are 
nevertheless eloquent and to the point. The portion omitted from the 
present edition is the reply of Dr. Young to the Edinburgh “ Reviewers.” 
This was introduced into the former edition, which was really an American 
publication, and it has served the purpose for which it was originally pub- 
lished. Hence it loses its place in the work now before us, and in its stead 
is an admirable engraving of Dr. Young, which has been well executed by 
Mr. Adlard, from the painting by Sir T. Lawrence. 
It is in the “ Sound,” which is a work nearly twice the size of the former, 
and which is in its third issue, that the most remarkable additions have 
been made. Since the second issue the author has been carrying through 
(for the Trinity House) a very remarkable series of experiments, and he has 
been led by these to the formulation of certain doctrines which he thinks are 
definitely conclusive. On this point Professor Tyndall has been directly at 
variance with the conclusions already drawn up by the Light-house Board 
at Washington; a circumstance which is somewhat unfortunate, even 
though, as it seems most probable, Professor Tyndall is clearly in the right. 
It is on this account, doubtless, that the author enters at such length into 
the discussion of the entire question. And from a perusal of the facts, as 
set forth by Dr. Tyndall, it would certainly appear that he is clearly correct, 
and the Americans inaccurate in their account. This seems so from the 
fact, which is particularly dwelt on by the author, viz., that “ the echoes 
have often manifested an astonishing strength when the sea was of glassy 
smoothness. On days when the echoes were powerful I have seen the 
southern cumuli mirrored in the waveless ocean in forms almost as definite 
as the clouds themselves. By no possible application of the law of incidence 
could the echoes from such a sea return to the shore ; and if we accept for a 
moment a statement which Professor Henry seems to endorse, that sound- 
waves of great intensity, when they impinge upon a solid or a liquid surface, 
* “ Six Lectures on Light, delivered in America in 1872-73.” By John 
Tyndall, LL.D., F.R.S. Second edition. And “ Sound.” By John Tyn- 
dall, LL.D., F.R.S. Third edition. London : Longmans, 1875. 
