198 
NATURE 
[APRIL 22, I915 

excluded. The author regards “the control of 
sex in Man as an achievement not entirely im- 
possible of realisation.” 
As regards the differences between the sexes, 
with which the author is not specially concerned 
in this volume, the view is entertained that ‘‘the 
physiology of the female is relatively anabolic, 
that of the male catabolic in character. That 
this should be so is perhaps a necessary conse- 
quence of the difference in function between the 
sexes. . . . It is interesting to speculate, how- 
ever, whether the active, vigorous habits of the 
male and the restless movement of the sperma- 
tozoon on the one hand, and the quieter habit of 
the female and the passivity of the egg on the 
other, may not each be due to fundamental cata- 
bolic and anabolic tendencies, characteristic of 
maleness and femaleness, quite apart from the 
exigencies of reproduction.” 
This speculation is luminous and interesting, 
but we should have liked it better if reference had 
been made to the fact that it was advanced more 
than a quarter of a century ago by Prof. Patrick 
Geddes. It may be, however, that this is just 
another illustration of great minds thinking alike. 
X-RAYS AND CRYSTALS. 
X-Rays and Crystal Structure. By Prof. W. H. 
Bragg and W. L. Bragg. Pp. vii+229. 
(London: G. Bell and Sons, Ltd., 1915.) Price 
7s. Od. net. 
BOOK in which are gathered together the 
results so far obtained in the new field of 
research concerning X-rays and crystals is parti- 
cularly welcome at the present time, and especi- 
ally from Prof. Bragg and his son. For not only 
have they carried the subject very much further 
than its initiators, Drs. Laue, Friedrich, and 
Knipping, but they have also given us an en- 
tirely new mode of experimenting. Indeed, in 
the hands of the English observers the investiga- 
tion has already borne surprisingly important 
results, both as regards experimental confirma- 
tions of the views of crystallographers based on 
crystal measurement and as regards the nature 
of the X-rays themselves. The book will be 
gladly received by all who desire to explore the 
possibilities of the new method of attack, as it 
affords much-needed detailed descriptions of the 
apparatus employed, and instructions for its use. 
The photographic diffraction method of Laue 
only receives a relatively small amount of atten- 
tion, as the Bragg method, which involves the 
use of the X-ray spectrometer, is shown to be 
much more capable of affording indications of 
the internal structure of the crystal in the more 
complicated cases. It is clearly shown, how- 
NO. 2373, VOL. 95] 

ever, that the two methods are mutually comple- 
mentary, and lead to essentially the same result, 
with the advantage of detail on the side of the 
spectrometer, and permanence of record on the 
side of the photographic radiogram. 
The whole subject is still so fresh that it might 
have been considered premature that a book 
should yet be written concerning it. But the 
results obtained already are so clear, and the 
stage reached may so truly be said to be one at 
which the initial difficulties have been overcome 
in the simpler cases tackled, that this book is in 
reality fully justified, and should prove of great 
use in attacking the immense difficulties which 
are presented by the more complicated crystalline 
chemical compounds. It may be that our first 
transports over the opening-up of so remarkable 
a new field of research may have to be modified, 
as it appears to be Only capable of yielding unmis- 
takably intelligible indications in the very 
simple cases, those of the chemical elements and 
their binary and ternary compounds, and not to 
be generally capable of indicating hemihedrism. 
For Friedel has shown that only eleven different 
types of radiogram are afforded by the thirty- 
two classes of crystals. It was hoped that it 
might throw a clear light on the much-discussed 
Pope-Barlow conception of valency, as dependent 
on the relative volumes of the spheres of influence 
of the various elementary atoms in a crystalline 
compound. But so far the indications are not 
favourable to that theory, and have led its pro- 
pounders to doubt the value of the X-ray results. 
The chief substance studied which has afforded 
indications is the diamond, the analysis of which 
with the aid of the X-ray spectrometer is perhaps 
the most brilliant piece of work carried out by 
the Braggs. \Vhatever its indications may be as 
to the nature of the packing of the atoms and the 
sizes of their spheres of influence, there can be no 
doubt that the structure arrived at in the case of 
this, the most interesting, form of carbon is one 
which must commend itself both to the crystallo- 
grapher and to the organic chemist as bearing 
the impress of truth. 
The book will be found to afford much informa- 
tion concerning the properties of X-rays, as 
revealed by the Bragg spectrometer, and details 
of the investigations of all the simple crystalline 
substances which they have studied by its aid. 
The main work of the authors has been to show 
that the different orders (first, second, and third) 
of reflection, at the specific angles for maximum 
effect experimentally found for certain ‘“‘mono- 
chromatic’ X-radiations, correspond to reflec- 
tions from different sets of planes among the 
whole parallel series of planes of atoms present in 
