OcTOBER 19, 1916] 
NATURE 
127 
THREE TEXT-BOOKS OF PHYSICS. 
(1) A Manual of Practical Physics. By H. E. 
Hadley. Pp. viiit+262. (London: Macmillan 
and. Co., Ltd., 1916.) Price 3s. 
(2) Text-book of Mechanics. By Prof. Louis A. 
Martin, jun. Pp. xviii + 313. Vol. vi: 
Thermodynamics. (London: Chapman and 
Hall, Ltd., 1916.) Price 7s. 6d. net. 
(3) An Intermediate Text-book of Magnetism and 
Electricity. By G. F. Woodhouse. Pp. x+ 
264. (Sedbergh: Jackson and Son, 1916.) 6s. 
net. 
[#4 is always of interest to study text-books 
written by those engaged in teaching, and to 
note the special points which their experience as 
teachers leads them to emphasise. 
(1) Mr. Hadley, who is principal of the School 
of Science at Kidderminster, is the author of a 
number of excellent works on physics, and the 
present small volume gives further proof of his 
ability as a clear exponent of physical principles. 
The book is suitable for the upper classes at 
schools where practical physics forms, as it should 
do, part of the science course. It is scarcely 
correct to say that it covers the work necessary 
for a present-day intermediate course, as many of 
the experiments described are qualitative rather 
than quantitative, and some are more suitable for 
the teacher to demonstrate in front of his class 
than for the students themselves to carry out. A 
noteworthy feature is the simple apparatus 
required for most of the work—the determination 
of the centre of gravity of a wickerwork basket 
suggests a new use for the editorial wastepaper 
basket ! 
It is open to question whether it is desirable to 
retain the definition of specific heat as a ratio 
(p. 116). In actual practice what is required most 
frequently is the ‘thermal capacity of unit 
mass,” which is expressed in calories per gram 
per degree. Unless this is used the “dimensions ” 
of an ordinary heat equation are incorrect. We 
may note in passing that for the same reason the 
value of a latent heat should be expressed, not in 
calories (p. 122), but in calories per gram. It 
has been pointed out in Nature (vol. xcv., p. 427) 
that the British use of “specific” is hopelessly 
inconsistent, and it is only necessary to compare 
the definition of specific resistance on p. 225 with 
that of specific heat to appreciate the absurdity 
of our present nomenclature. A new term to 
denote the thermal capacity of unit mass of a 
substance is much to be desired. 
A series of observations with an ammeter and 
a tangent galvanometer is followed by the remark : 
“This demonstrates that the current is propor- 
tional to the tangent of the angle of deflection.” 
As the tangent galvanometer is an absolute instru- 
ment, it is obvious that no such ‘result can be 
proved by its use. 
(2) Prof. Martin has produced a useful text- 
book on thermodynamics for engineering students. 
It forms the sixth volume of a series by:the same 
author. Without going into excessive detail the 
writer has succeeded in giving a remarkably clear |} being unsatisfactory. 
NO. 2451, VOL. 98] 
outline of the essentials of the subject. Although 
the treatment is elementary, differential equations 
are used throughout, their meaning being ex- 
plained in such a way as to lead the student 
forward step by step. A large number of numeri- 
cal exercises are provided throughout the work 
and at the end of the book. British thermal units 
are alone employed. The diagrams are very good, 
and the typography is such as to give every assist- 
ance to the student in his study of the subject. 
(3) The “Intermediate Text-book of Magnetism 
and Electricity,’ by Mr. Woodhouse, senior science 
master at Sedbergh School, combines practical 
instruction with theoretical discussion. A large 
number of simple experiments described in the 
text may be carried out by the student with no 
great outlay in apparatus. The author is prob- 
ably right in saying that the electrolytic definition 
of the unit of current is more readily grasped by 
the average student than the electro-magnetic, 
but we are of opinion that greater emphasis 
should be laid on the distinction between the prac- 
tical definitions of electrical units (the so-called 
international units) and the absolute definitions. 
The book would be much improved by a careful 
revision: the style is frequently curt and some- 
times inelegant. Many students have been 
penalised in examinations for giving as the second 
law of electrolysis: ‘“‘The weight of an element 
deposited is proportional to the electro-chemical 
equivalent.” The strength of a magnetic field is 
not measured in dynes (p. 53), but in dynes per 
unit pole or gausses. 
We strongly endorse the opinion of the author 
that all students of physics should learn the 
calculus. A portion of Appendix I. is devoted to 
explaining, briefly, the principles and method of 
differentiating and integrating simple quantities. 
Several well-known text-books of physics are 
marred by attempts to eyade the use of the cal- 
culus. It is far better to adopt the author’s plan 
and devote a little space and time to introducing 
the elements of the calculus than to employ 
tedious and unnecessary investigations which are 
only differentiation or integration in disguise. 
Appendix II. contains a description by Mr. 
J. W. Shepherd of a wireless set which, in more 
favourable days than the present, may be set up 
by the student who has obtained permission from 
the Postmaster-General. 1 (ats pe fs 
OUR BOOKSHELF. 
Le Climat de la France: Température, Pression, 
Vents. By G. Bigourdan. Pp. 135. (Paris: 
Gauthier-Villars et Cie.) - Price 4-fr. 
Tuis publication, dealing particularly with tem-’ 
perature, - pressure, and winds, is rather a com- 
pilation than otherwise, free use being made of 
the original scientific discussions by M. Angot. 
Temperature observations made in France go 
back to the middle of the seventeenth century, 
but, as in other countries, the early observations 
were made with imperfect instruments, and the 
exposure was often bad, the results in consequence 
There are only fourteen 
‘ 
