August 9, 1918] 
In the teaching of photography to students 
the tendency has been to lay great emphasis 
on the chemistry of the subject while the 
physies of photography, which is at least as 
important as the chemistry, has too often been 
ignored. Dr. Roebuck has approached the 
subject from the standpoint of the physicist 
rather than from that of the chemist, with the 
result that in this book there is given a clear 
and valuable exposition of the elementary 
principles of sensitometry, that is, of the prop- 
erties of photographic material and its be- 
havior during exposure and development. 
The chemistry of the book is distinctly 
weak, there is practically no discussion of the 
chemistry of development, and the few equa- 
tions given for the action of developers are very 
much open to question. There are also a few 
obvious errors in chemistry such as the state- 
ment that Stas was a German, or that hydro- 
chlorie acid can be added to silver nitrate in 
order to produce an acid emulsion. 
In the portion of the book dealing with gen- 
eral theory the author commences with a brief 
chapter on the historical development of the 
subject and then deals with the sensitometry 
of the gelatine dry plate. A short chapter 
then discusses the subject of color sensitive- 
ness, and another, theories of the latent image. 
Further chapters deal with negative defects, 
a very practical chapter indeed, positive proc- 
esses, lenses, color photography, and the gen- 
eral principles of composition. 
The second part of the book consists of a 
laboratory manual containing a series of ex- 
periments to be performed by the student. 
This will be very valuable to any teacher ar- 
ranging a course in photography and a stu- 
dent who has worked thoroughly through the 
course, repeating the more elementary portions 
several times, will have had a good training in 
the elements of the subject. 
On the whole the book forms a valuable ad- 
dition to the scanty list of modern works on 
photography and is to be recommended to all 
those who are interested in the scientific side 
of the subject. 
C. E. K. Megs 
RocHester, N. Y. 
SCIENCE 
141 
THE PROCEEDINGS OF THE NA- 
TIONAL ACADEMY OF SCIENCES 
Tue first number of Volume 4 of the Pro- 
ceedings of the National Academy of Sciences 
contains the following articles: 
The Basal Katabolism of Cattle and Other 
Species: Henry P. Armsby, J. August Fries 
and Winfred W. Braman, Institute of Animal 
Nutrition, the Pennsylvania State College. 
The results show that the basal katabolism of 
different species is substantially proportional 
to their body surface. 
The Location of the Sun’s Magnetic Axis: 
F. H. Seares, A. van Maanen and F. Ellerman, 
Mount Wilson Solar Observatory, Carnegie 
Institution of Washington. In extension of 
the work of George E. Hale, a large number 
of observations were undertaken to determine 
the position of the sun’s magnetic axis, which 
is found to lie near the axis of rotation at an 
inclination of about 6°, and to revolve about 
the axis of rotation in about 32 days. 
Resonance and Ionization Potentials for 
Electrons in Cadmium, Zine and Potassium 
Vapors: John T. Tate and Paul D. Foote, Uni- 
versity of Minnesota and Bureau of Stand- 
ards. The results agree within the limits of 
experimental error with the values as calcu- 
lated from the quantum relation hy=eV, 
where yp is the frequency of the single radiation 
in the case of resonance potentials or the 
limiting frequency of the series of radiations 
in the case of ionization potentials. 
The Validity of the Equation P=dv/dT in 
Thermo-Electricity: Edwin H. Hall, Jefferson 
Physical Laboratory, Harvard University. 
The equation is known to be unverified experi- 
mentally. The author gives a brief, critical 
discussion of the validity of some theoretical 
proofs by which the equation has been de- 
duced. 
On the Equations of the Rectangular Inter- 
ferometer: Carl Barus, Department of Physics, 
Brown University. A discussion under the 
under the headings of: Auxiliary Mirror, 
Rotating Doublet, Ocular Micrometer, Colli- 
mator Micrometer. 
