542 
Notices of Books. 
[October, 
sunlight — which, from the context, appears to be the peculiar 
change here referred to — has been carefully observed some 
time ago. 
On the other hand, what may be called the stridfly photographic 
portion of the work is very valuable. 
The chapter on the “ correctness of photographs,” in which 
the author treats of the individuality of the photographer, of the 
influence of lenses, of the length of exposure, of colours and 
models, of the characteristic feature in the picture, of deviation 
from truth in photography, and of the difference between 
photography and art, may be read with great advantage by 
photographers, artists, and amateurs. Prof. Vogel does not 
countenance the popular notion that a photograph is necessarily 
and invariably more correCt than a picture. We think that it is 
Nathaniel Hawthorn who maintains that the character of a 
person is more truly shown in his photographic likeness than in 
his face. That this may not have been incidentally the case we 
are not prepared to deny ; but it is certainly not the rule. On 
the contrary, photography is apt to flatter one class of persons, 
and in revenge to be less than just to another. Among the 
latter are often found those whose principal attraction depends 
more on the play of expression than upon strict regularity of 
feature. 
The author figures and recommends aphotometerfordetermining 
the exaCt time needful for exposure. It will doubtless be evident 
that for this purpose the radiometer will probably prove highly 
valuable. The chapter on “ photography in natural colours ” 
gives an account of certain attempts made to solve this inte- 
resting problem, and recalls to our memory a strange hoax suc- 
cessfully perpetrated many years ago. It was announced that 
the art of taking coloured photographs had been discovered in 
America, and a descriptive catalogue of the specimens on their 
way for exhibition in London “ went the round of the papers.” 
But the specimens never arrived, and the whole affair proved to 
be merely a most unjustifiable falsehood. 
The concluding chapter, on photography as a subjeCb to be 
taught in industrial schools, is worth the serious attention of 
educational boards. Of course the term “ industrial schools ” is 
used here in its natural acceptation, and not in the strangely 
perverted meaning which has been forced upon it in England 
within the last few years. 
The Principles of Dynamics ; an Elementary Text-Book for 
Science Students. By R. Wormell, D.Sc. London, Oxford, 
and Cambridge : Rivingtons. 
The author remarks, in his Preface, that “ the objedt of the 
present work is to present and unfold the subject according to 
