537 
Braces (and also with the data, they have obtained with their own 
method of erystal-photography). In my opinion however they neglect 
an important element in their reasoning and in this state of things 
nothing can be said about the existence or non-existence of such 
rings of electrons on account of data about scattering of Röntgen- 
rays. This | hope to prove in the following. To this purpose | intend 
to follow the clear method in which Brace has treated the subject. 
We consider the octahedronplanes (the planes (111) in the usual 
notation), which contain the C-atoms, e.g. the plane A, B,C, F,G,H 
(see fig. 1), a second plane contains D, a third £. All these planes 
contain an equal number of 
atoms, their mutual distance 
is alternately + d and ? d, 
as represented by fig. 2. 
If we only regard the reflec- 
tion by the planes a, accord- 
ing to the ordinary suppo- 
sitions we shall have a 
maximum intensity in the 
reflected beam for 
2d sin p = nA, 
here 7 has the values 1, 2, 
3 etc. Regarding also the 
planes a’ we see that the spectrum of the 2"¢ order (n = 2) disappears, 
because the planes a’ give half a wave- 
length phase-difference with the planes 
a. For the same reason the spectrum 
of the 6% order would disappear. 
Fig. 1. 
The Braces have observed with the 
use of Rh.-K-rays spectra as far as and 
including that of the 5 order; of the 
spectrum of the 2°¢ order nothing could 
be detected. This very result has given 
them one of their strongest arguments 
in favour of the erystalmodel they 
suggested. With the model of Dugum b------------—- ‘ 
and Scnerrer it is another case. In i= 
the usual way they assume, that the Der See wen 
scattering is only caused by the electrons Lissa zi 
and may be calculated in the classical ei : 
5 : 3 Fig. 2 and 3. 
manner. In their caleulations they 
