540 
First however the intensity decreases in general with the order of 
the spectrum’); secondly the intensity which we should expect 
according to (2) is very small, because J, (lx) is again negative for 
nm = 6 for the considered value of 7 (about 0,55.10—8 e.m.). 
Now it is interesting to consider the reflection by the other erystal- 
planes. Here we shall follow the method also used by DeBrw and 
SCHERRER. When we have a regular erystal, then the intensity of a 
beam retlected according to the relation of Brace is proportional to 
the square of the so-called structure-factor®) S, which is given by 
Sa Sane Teh Pn eh) vo eee 
Here A, is proportional to the amplitude of the beam radiated 
by the zt" centre of the fundamental cube, pn grin are the ordinates 
of this centre in the cube, whose edge is 1; h,h, h, are the indices 
of the considered crystalplane. These may have a common divisor. 
If they are for instance 024, then the spectrum of the Ard order of 
the plane 012 in the ordinary notation is meant. 
For Brace’s crystalmodel this factor is: 
Be. „ir Gelet) Na Relea SE Sade cy 
DerByr and ScHERRER assume that the connecting-ring scatters in 
the same way as the nucleus-electrons. Also for their model we 
may put all A,’s=1. 
Therefore they obtain: 
iS Oale) iS athe ths) i= at) 
+e 14e 4 
— 
Spe (tee 
leah cana. gen Cal) eee (07) 
im (hj +h i = (hath) iz (hath 
ie gi all ar otk sal) 
Taking into consideration the position of the orbits of the ring- 
electrons in the above-given way, we get for the structure factor: 
i= (yp he bh BE) 
S=2lite? Et Oe | 
i= (hath i= (hgh itho) | 
rede jee E 
iz (hy +h) ix (hath ix (hs+hy) } | 
‘des Taig ed a ak 
Here 7 and x have the same signification as in (2) and (3); the 
indices at the different magnitudes / refer to the four different angles 
1) See e.g. Braga. Proc. Roy. Soc. A. 89, p. 279, fig. 2. 
2) See D. and Scr. Phys. Z. S. (1916), p. 279. 
For the meaning of this factor see: Marx. Handb. d. Rad. Bd. V. p. 581. 
