46
NOTES
U n i o n , b u t all c r y s t a l l o g r a p h e r s a r e c o r d i a l l y i n v i t e d to
a t t e n d t h e I n t e r n a t i o n a l Congress. T h o s e o u t s i d e of t h e
U . S . A . e x p e c t i n g to be p r e s e n t are r e q u e s t e d to i n f o r m
t h e G e n e r a l S e c r e t a r y a t a v e r y e a r l y d a t e in o r d e r t h a t
d e t a i l e d p l a n n i n g m a y p r o c e e d w i t h o u t d e l a y ; t h o s e willing to c o n t r i b u t e p a p e r s s h o u l d a t t h e s a m e t i m e f o r w a r d
d e t a i l s for c o n s i d e r a t i o n b y t h e P r o g r a m m e C o m m i t t e e .
C r y s t a l l o g r a p h e r s in t h e U . S . A . will r e c e i v e s e p a r a t e
n o t i f i c a t i o n f r o m t h e A . S . X . R . E . D . or t h e C r y s t a l l o g r a p h i c S o c i e t y of A m e r i c a . I t will u n f o r t u n a t e l y n o t
be possible for t h e U n i o n to p r o v i d e f u n d s t o assist
d e l e g a t e s in a t t e n d i n g t h e Congress a n d c r y s t a l l o g r a p h e r s
s h o u l d t h e r e f o r e m a k e t h e i r o w n a r r a n g e m e n t s in t h i s
matter.
kX and Angstr6m units
T h e following l e t t e r is r e p r i n t e d b y p e r m i s s i o n f r o m J. Sci.
Instrum. (1947), 24, 27:
At the annual conference of the X-ray Analysis Group of the
Institute of Physics in July 1946 it was announced that agreement had boon reached concerning the factor for converting
measurements in k X units to ,3~gstr6m units. The factor
agreed upon, after consultation with the American Society for
X-ray and Electron Diffraction and Prof. Siegbahn was 1-00202.
This factor is probably correct to 0.003 %. Since wave-lengths
in X-units have boon measured to an accuracy of 0.001%, the
wave-lengths in Angstr6m units can be taken as accurate to
0.004 % in general.
The following is a list of values of wave-lengths in Angstr6m
units of certain omission lines and absorption edges in common
use. The column headed K a gives the mean value of Ka~ and
K~ 2, K~ 1 being allowed twice the weight of Kay.
Current values of the physical constants, such as those
AND
NEWS
quoted by Birgo in the 1941 volume of the Physical Society'~
Reports on Progress in Physics, should be used in conjunction
with these wave-lengths. In particular, density p is given by
the equation
p= 1.66020 ZA/V,
where EA is the sum of the atomic weights of the atoms in tlm
unit cell, and V is the volume of the unit cell in A s.
Ka x
Cr
Mn
Fe
Co
Ni
Cu
Zn
Me
Rh
lad
Ag
2-289
2.101
1.935
1.788
1-657
1-540
1.435
0-709
0.613
0.585
0.559
62
74
97
90
83
50
10
26
26
45
41
K%
2.293
2.105
1-939
1.792
1.661
1-544
1.438
0.713
0.617
0.589
0.563
K~
52
70
91
79
68
34
94
54
62
82
81
2.290 9
2.103 1
1.937 3
1.790 2
1.659 1
1-541 8
1-436 4
0.710 7
0.614 7
0.586 9
0.560 9
K flx
2-084
1-910
1.756
1.620
1.500
1.392
1.295
0.632
0.545
0.520
0.497
79
16
54
73
08
17
20
25
59
52
01
Absorption
edge
2.070 1
1.895 4
1-742 9
1.607 2
1.486 9
1.380 2
1.283 1
0.619 7
0.534 1
0.509 0
0.485 5
I t is recommended that in any published work the values of
the wave-lengths used should be explicitly stated.
W. L. BRAGG, Chairman,
X-ray Analysis Group of the Institute of Physics
Cavendish Laboratory,
Cambridge, England
A u t h o r s of p a p e r s i n t e n d e d for p u b l i c a t i o n in Acta
Crystallographica are r e q u e s t e d to express cell d i m e n s i o n s
a n d r e l a t e d q u a n t i t i e s in A n g s t r 6 m u n i t s a n d , w h e n t h e
a c c u r a c y of t h e w o r k justifies t h e d i s t i n c t i o n b e t w e e n t h e s e
a n d k i units, to a v o i d all possible confusion b y q u o t i n g
also e x p l i c i t l y t h e w a v e - l e n g t h of t h e r a d i a t i o n used.
Book Reviews
Works intended for notice in this column should be sent direct to the Editor (P. P. Ewald, The Queen's University, Belfast,
Northern Ireland). A s far as practicable books will be reviewed in a country different from that of publication.
Grundlagen der allgemeinen Mineralogie und
Kristallchemie. By F. MACHATSCHKI.Pp. vii + 209,
w i t h 151 figs. S p r i n g e r V e r l a g , V i e n n a , 1946. P r i c e ,
16 s c h i l l i n g s ; $2.80.
Professor M a c h a t s c h k i , w h o n o w occupies t h e c h a i r of
m i n e r a l o g y in t h e U n i v e r s i t y of V i e n n a , h a s b e e n assoc i a t e d w i t h t h e d e v e l o p m e n t of t h e X - r a y analysis of t h e
c r y s t a l s t r u c t u r e of m i n e r a l s since 1927. F o r a t i m e he
j o i n e d t h e g r o u p of brilliant r e s e a r c h w o r k e r s w h o f o r m e d
t h e B r a g g school in M a n c h e s t e r a n d first s u g g e s t e d in outline t h e f r a m e w o r k of t h e felspar s t r u c t u r e s . Since t h e n
he has p r o d u c e d a n u n c e a s i n g flow of p a p e r s r a n g i n g over
t h e w h o l e field of m i n e r a l c h e m i s t r y .
T h e b o o k n o w u n d e r r e v i e w is a w e l l - w r i t t e n , clearly
p r i n t e d , a n d a d e q u a t e l y i l l u s t r a t e d class-book s u i t a b l e for
t e a c h i n g e l e m e n t a r y s t u d e n t s . I t is d i v i d e d into t h r e e
m a i n sections; c r y s t a l l o g r a p h y , c r y s t a l physics, a n d
c r y s t a l c h e m i s t r y , a n d c o n c l u d e s w i t h b r i e f a c c o u n t s of t h e
genesis of crystals, e t c h figures a n d p s e u d o m o r p h s . P a r t i c u l a r l y c o m m e n d a b l e are t h e i n t r o d u c t i o n s to c r y s t a l
optics a n d c r y s t a l c h e m i s t r y . T h e a u t h o r ' s m e t h o d of
t a b u l a t i n g t h e t h i r t y - t w o c r y s t a l classes, h o w e v e r , is less
in k e e p i n g w i t h t h e u p - t o - d a t e t r e a t m e n t in t h e rest of
t h e book. A l t h o u g h t w o s y s t e m s of n a m i n g t h e c r y s t a l
classes are given, only Schoenflies s y m b o l s are used. Most
t e a c h e r s of t h e s u b j e c t will r e g r e t his missing t h e c h a n c e of
i n t r o d u c i n g s t u d e n t s as soon as possible to t h e simpler a n d
more elegant Hermann-Mauguin nomenclature.
British Museum (Natural History),
London, S . W . 7,
England.
F . A . BANNISTER
Die Bewegungsgruppen der Kristallographi¢. By
J. J. BURCKHARDT. Pp. 189, with 56 figs. Verlag
Birkh/~user, Basel. Price, 29 Swiss francs.
This b o o k r e p r e s e n t s t h e result of a t w e n t y - y e a r investig a t i o n of t h e intrinsic m a t h e m a t i c a l t h e o r y of t h e crystallog r a p h i c groups. I n t h e w o r d s of B u r c k h a r d t : ' M i c h h e u t e
y o n dieser A r b e i t zu t r e n n e n , f/~llt m i r s c h w e r : w/~hrend
z w a n z i g J a h r e n w a r sie m e i n S t a b u n d m e i n e Stfitze
zugleich.' T h e basic p o i n t of v i e w of t h e b o o k r e s e m b l e s
closely t h a t a d o p t e d b y t h e r e v i e w e r in a series of articles
in t h e Zeitschrift fi2r Kristallographie in t h e e a r l y 1930's
u n d e r t h e title ' A M a t r i x - A l g e b r a i c D e v e l o p m e n t of t h e
C r y s t a l l o g r a p h i c G r o u p s ' . T h a t is, an a t t e m p t is m a d e to
a b s t r a c t t h e process ofderixdng t h e c r y s t a l l o g r a p h i c g r o u p s
f r o m t h e s o m e w h a t e a r t h - b o u n d tactics of s t r a i g h t - e d g e
a n d c o m p a s s g e o m e t r y used b y t h e g r o u p of t h e o r e t i c a l