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criteria do n o t uniquely d e t e r m i n e t h e space group,
a n d until such t i m e as t h e latter would become k n o w n
from other properties, such as morphology, piezoelectricity, pyroelectricity, optical activity, intensity
statistics, or a structure determination.
Note that, in the monoclinic and orthorhombie systems,
all possible orientations are foreseen. T h e y are collected
in braces. All t h e symbols given m a y be needed w h e n
t h e cell edges are labelled according to metric considerations (for instance, monoclinic : c < a; orthorhombic :
c<a<b).
I n Laue class 3m aspect P3** has been split into
P 3 * l a n d P31*; a n d aspect P31,921 and P31,~12. I n
each case the distinction can be m a d e on upper level
photographs (Bokii & Porai-Koshits, 1952).
W e wish to t h a n k Dr Gabrielle D o n n a y for a critical
reading of the manuscript.
References
BUERGEI~, M. J. (1942). X-ray Crystallography. New
Y o r k : Wiley.
Crystal Data (1963). A.C.A. Monograph No. 5. B r o o k l y n :
American Crystallographic Association.
DONNAY, J. D. H. & HA_RKER, D. (1940). Naturaliste
canadien, 67, 33, 160.
International Tables for X-ray Crystallography (1952).
Vol. I, pp. 347 et seq. B i r m i n g h a m : K y n o c h Press.
BoKII, G. B. & PORAI-KOSHITS, M. A. (1952). Praktischeskii Kurs Rentgeno-strukturnogo Analiza, Vol. I. Moscow: University Press.
Book Reviews
Works intended for notice in this column should be sent direct to the Editor (A. J. C. Wilson, Department of Physics, University College, Cathays Park, Cardiff, Great Britain). A s far as practicable books will be reviewed in a country different
from that of publication.
Electron Microscopy and Strength of Crystals.
Edited by G~Ta
THOMAS a n d JACK WASHBURN.
:New Y o r k : I n t e r s c i e n c e , 1963. Pp. x i + 1 0 2 2 . Price
£11.
All the old favourites are here: A m e l i n c k x a n d Delavign e t t e on dislocations in layer structures; K e h and
W e i s s m a n n on b.c.c, metals; Marcinkowski on superlattices; Nicholson on t h e nucleation of precipitates;
Price on hexagonal crystals; Segall on fatigued metals;
Thomas on precipitation h a r d e n i n g alloys; Swann on
dislocation a r r a n g e m e n t s in f.c.c, metals; W a s h b u r n on
MgO; W h e l a n on defects produced by quenching a n d
irradiation. These articles contain little t h a t is new,
but serve as an introduction for a research s t u d e n t to
t h e various i m p o r t a n t aspects of transmission electron
microscopy.
English metallurgists should read w i t h particular
interest t h e two loosely related papers from S t u t t g a r t
by Mader a n d by Seeger, Mader & Kronmiiller. These
bring t o g e t h e r a range of ideas and references which
will prove as valuable as Seeger's famous Lake Placid
(1957) article. There are also particularly interesting
articles by Friedel and Saada; t h e former condensing
w h a t seems to be slightly more t h a n his book into forty
pages.
I t is rem~rk~bl~ how tittle impact electron microscopy
has m a d e on t h e theories of t h e strength of crystals.
Most of the theories proposed at this conference have no
basis in t h i n foil observations. Few people have indeed
troubled to m a k e t h e sort of detailed correlation between
microstructure a n d mechanical properties which is
required for further advance. Exceptions which spring
to m i n d are Ashby's a t t e m p t to correlate flow-stress a n d
particle spacing in internally oxidized alloys, and so to
confirm Orowan's t h e o r y of strength, and, of course,
the slip-line-stress-strain curve studies of the S t u t t g a r t
School. These serve to show w h a t can be done.
This collection of papers gives us the by now familiar
story of how powerfully transmission microscopy can
provide q u a n t i t a t i v e information on a wide range of
metallurgical investigations; information, t h a t is, on a
micron or hundred-.hmgstr6m scale. ~That t h e collection
only hints at is the still obscure and fascinating question
of the cooperative a n d d y n a m i c behaviour of m a n y
dislocations in a straining crystal.
The book can be said to be a timely s u m m a r y of a
specialized field, and if it were not so highly priced,
it would be a useful addition to every microscopist's
library.
L. M. BRow~
Cavendish Laboratory
Free School Lane
Cambridge
England