Marcu 25, 1915] 
NATURE 

alternative to sterilisation put forward by Dr. 
Houston in his reports to the Metropolitan Water 
Board—namely, adequate storage followed by 
efficient filtration—is not presented in its best 
light, and one is inclined to think a much better 
case could be made out from Dr. Houston’s 
reports in favour of his suggestions than is con- 
veyed by the somewhat meagre extracts given in 
the book. 
The different means of sterilising water are very 
fully described and discussed, both chemical 
(peroxides, excess lime, chlorine, and hypochlor- 
ites, etc.), and physical and electrical (electrolytic 
hypochlorite, ozone, and ultra-violet light), and full 
reference is made to the places where these pro- 
cesses are practised. 
The concluding chapter, on the analysis of water 
and the interpretation of results, is written more 
for the water authority than the analyst. It is 
not an easy subject to deal with, yet the authors 
appear to have done it very carefully. 
There are numerous excellent plates in the book 
illustrating different works and processes. 
Denison B. BYLeEs. 

RADIOLOGY IN THEORY AND 
PRACTICE. 
(1) X-rays: an Introduction to the Study oy 
Rontgen Rays. By Dr. G. W.C. Kaye. Pp. 
x+252. (London: Longmans, Green and Co., 
1914.) Price 5s. net. 
(2) A Manual of X-Ray Technic. By Capt. A. C. 
Christie. Pp. viiit+104. (Philadelphia and 
London: J. B. Lippincott Company, n.d.) 
Price 8s. 6d. net. : 
(3) Molecular Physics. By J. A. Crowther. Pp. 
viii+167. (London: J. and A. Churchill, 1914.) 
Price 3s. 6d. net. 
(1) HE discovery of X-rays has hitherto 
afforded an opportunity, probably unique 
in the history of science, for the production of that 
kind of literature which is distinguished more for 
its sensational character than for its accuracy or 
usefulness. If the numerous small books and 
pamphlets dealing with the subject and published 
between 1895 and 1898 do not seem to us now to 
possess any striking feature, they are at least re- 
markable for their resemblance to one another. 
They serve, too, as a measure of the wide popular 
interest aroused by Prof. Réntgen’s work. Some 
of these publications actually reached the six 
thousandth edition before finally sinking into 
oblivion. When it was realised, however, that 
X-rays, in conjunction with the study of radio- 
activity, were destined to play a vital part in the 
elucidation of many problems hitherto considered 
NO. 2369, VOL. 951 

87 
insoluble, and a few well-known laboratories had 
successfully taken the matter in hand, the budding 
heralds of a new physics seem to have lost their 
spirit. It is noteworthy that from about 1898 until 
now, excepting some medical works, including an 
account of radiation treatment, no English book 
has appeared devoted solely to the systematic 
study of Réntgen radiation. 
Dr. Kaye’s book will therefore be welcomed by 
all who are engaged in work with the new radia- 
tions generally and with X-rays in particular, for 
it has appeared at the very moment when it is 
most needed. 
The time has certainly come to take stock of our 
knowledge of this subject and to set forth clearly 
the relationship which connects the speed of the 
electron with the wave-length of the radiation 
resulting from its impact against a specific sub- 
stance. Incidentally, it is seen that the production 
of a radiation identical with the gamma rays from 
radium is merely a question of overcoming certain 
experimental difficulties, and obstacles of this 
character generally disappear with the lapse of 
time. The first part of Dr. Kaye’s book deals 
in an interesting manner with some of the early 
classical vacuum-tube experiments, and care is 
taken, by the aid of numerous asides in the form 
of footnotes, to give the reader many useful facts 
as well as references. 
The fourth chapter deals with the X-ray bulb 
itself, and the progressive changes in its design 
are traced from the 1895 type, with flat electrodes, 
up to the somewhat elaborate modern apparatus. 
There are many excellent illustrations here, and 
the photomicrograph on p. 43, of an anti- 
kathode after prolonged use, is of great interest. 
A chapter follows in which the various high- 
potential generators of electricity are described. 
The references to influence machines, induction 
coils, and step-up transformers contain many prac- 
tical hints, and the oscillograph records are well 
reproduced. Next follows an account of the 
various interrupters and their several virtues or 
drawbacks, and a chapter dealing with the actual 
manipulation of an X-ray apparatus, wherein 
we are told about the volatilisation of the anti- 
kathode, the coloration of the glass, and so forth— 
all of great practical interest and importance to 
these engaged upon this work. The rest of the 
book is concerned with the more theoretical part 
of the subject and methods of measurement, ques- 
tions of wave-length, sparking potentials, absorp- 
tion coefficients, and soon. The work of Barkla 
and others on the secondary and characteristic 
radiations are fully set out, so that the reader 
may be gradually prepared for the final sections 
dealing with the actual nature of X-rays and the 
