474 
one end of the object to be measured exactly oppo- 
site to the first unit mark”; the position of both 
ends of the object should be read off, the fraction 
of a division being estimated by the eye. We 
cannot agree with the author’s claim on p. 194 
that the apparatus described for measuring the 
expansion-coefficient of air at constant pressure 
gives better results than any form usually em- 
ployed in schools. He has in the example cited 
a movement of the mercury column of 4°93 cm., 
and it would be very difficult to estimate this 
exactly to more than 1 mm. ‘There is confusion 
in the definition of thermal conductivity, the ex- 
pression “a centimetre cube” would have been 
better than “a cubic centimetre,” and the coefh- 
cients of thermal conductivity in the table on 
p. 245 are not in calories. The large number of 
questions and numerical exercises should prove a 
great boon to many teachers. 
(3) “‘ Practical Physics for Secondary Schools,” 
by Black and Davis, is not a laboratory manual, 
but what in England would probably be termed 
a “Textbook of Elementary Physics.” The 
authors, in the preface, state that in preparing 
the volume they have tried to select only those 
topics which are of vital interest to young people, 
whether or not they intend to continue the study 
of physics in a college course. They believe that 
everyone needs to know something of the work- 
ing of electrical machinery, optical instruments, 
automobiles, vacuum cleaners, fireless cookers, 
&c, It must not be thought, however, that the 
fundamental principles of physics have been ne- 
elected; Messrs. Black and Davis have succeeded 
in producing a very clear and interesting text- 
book. In the chapters devoted to optics we have 
the proof of the mirror formula, 1/D)+1/D,=1/f, 
but in the case of the lens the authors state the 
same formula holds. We should like to have seen 
it made more explicit as to the signs of the terms 
in the various cases which may arise. Fig. 444, 
combining spectral colours into white light by aid 
of a convex lens, is obviously wrong. The book 
contains a large number of questions and numeri- 
cal exercises, and there is much useful information 
in it which should prove of extreme value to a 
teacher, but it is scarcely suitable for adoption in 
English schools owing to its American style. 
(4) The first edition of Duff’s “Text-book 
of Physics” appeared in 1908, and was compiled 
by the collaboration of seven teachers of physics 
in the universities and polytechnic. institutes of 
the United States. In this third edition the sec- 
tions on heat and electricity and magnetism have 
been re-written, and are greatly improved. Prof. 
Mendenhall is responsible for the section on heat, 
and Prof. Carman for that on electricity and mag- 
NO. 2304, VOL. 92} 
NATURE 
, regarded as a text-book for those engaged in 
| ‘Physik des Aethers” was published, the book 
(| DecEMBER 25, 1913 
netism. Prof. McClung contributes a section on 
the conduction of electricity through gases. ‘The 
text-book forms an excellent college course on 
physics, and though, in a single volume, the 
treatment of some points must of necessity be 
meagre, there are references at the ends of each 
section to the various standard text-books deal- 
ing with special branches. 
(5) ‘‘Experimental Heat,” by A. W. Mason, 
is a laboratory course of experiments for second- 
ary schools, and thoroughly covers the syllabus of 
the Matriculation and Senior Locals. The book is 
well arranged, and each exercise is furnished with 
questions bearing on it. The answering of these 
by the pupil will certainly necessitate intelligent 
thought about the experiment he has performed. 
(6) It is more than eighteen years since Drude’s 
j 
. 
being the outcome of a course of lectures on Max- 
well’s Electromagnetic Theory delivered by the 
late Prof. Drude at the University of Géttingen. 
Although the book did not aim at being a com- 
plete treatise on electricity and magnetism, it 
formed an excellent introductory course to the 
standard work of Maxwell. The mathematical 
treatment was simple, no further knowledge than 
the elements of the calculus and differential equa- 
tions being demanded of the reader. In the new 
edition by Prof. W. Kénig, although the scope 
of the book remains the same, considerable modi- 
fications have been made which greatly enhance 
its value as a text-book of electricity. The first 
portion of this second edition is devoted to elec- 
trostatic theory, the treatment of which was ex- 
ceedingly meagre in Drude’s original work. The 
section dealing with Helmholtz’s “Action at a 
distance’ theory has been omitted, and also the 
chapters bearing on optical phenomena from the — 
electromagnetic point of view. These latter have 
been treated by Drude at much greater length in 
bis more recent “Lehrbuch der Optik.” The 
chapters on electrical oscillations have been ampli- 
fied, the theory of coupled circuits being included. 
The author has found it impossible to deal with 
the electron theory within the compass of the 
book. An excellent portrait: of the late Prof. 
Drude forms the frontispiece of the work. — 
OUR BOOKSHELF. 
Underground Waters for Commercial Purposes. 
By Dr. F. L. Rector. Pp. v+98. (New York: 
John Wiley and Sons, Inc. ; London: Chapman 
and Hall, Ltd., 1913.) Price 4s. 6d. net. 
Tue title of this book is rather misleading. AL 
though the contents are interesting and useful so 
far as they go, the book cannot in any way be 
