1279 
l 
of pulse thickness A, together having a thickness /’ = — A or 
m 
Rd which is a small quantity so long as A is small with respect 
m 
to /,, as is generally the case. When the pulses do coincide, which 
again will be the case when we take into account the primary dis- 
turbances of equilibrium emitted successively by the anticathode, then 
the considerations developed by Prof. Lorentz must be applied. Thus 
also when operating with the hypothesis that the RÖNTGEN rays 
exist in pulses, the incoherence of the pulses originating from 
the different parallel planes is a matter of fact, and therefore also 
on this assumption the intensity of the spots in the photogram 
will be proportional to the number of molecules pro unity of sur- 
face of the corresponding plane. We may suppose that in this 
direction also the solution is to be found of the question why the 
effect of the motion of heat which causes the molecules to vibrate 
around the corners of the net, is so small. 
Now we may still with a single word discuss the photograms 
which were at our disposal. 
The way in which they were taken agrees in many points with 
that of Laur, only it has been somewhat less complicated. In order to 
shorten the time of exposition, a fluorescent screen was used. The 
spots occurring on the plates may be arranged very conveniently into 
ellipses, hyperbolas, straight lines and sometimes parabolas; as BRAGG 
has already explained, points of such a conical section originate 
from the reflection on planes rich in molecules, which have a line 
rich in molecules in common. The conic section then will be the 
inter-section of the photographic plate and a cone, produced by letting 
the incident beam turn about the said line rich in molecules. 
The photograms at my disposal were: 
1. Rock-salt. The direction of incidence was lying along a cubical 
axis. The diagram produced agrees with the one for zinc-blende. The 
distance of the crystal from the photographic plate was 4 cm, 
while 3.56 in Lave’s experiment. By magnifying Lavr’s pattern in 
the corresponding proportion I got one perfectly congruent with 
that of Prof. Haca. Only a few ellipses were missing or were re- 
presented less intense, which may be attributed to the fact that 
with NaCl the net is centric cubical, whereas ZnS shows cubes 
with centric cube faces. This agrees with the erystallographically 
deducted cleavability, which lies in the direction of the plane richest 
in molecules. The fact that the patterns for matters of totally different 
kinds are identical, is a strong proof for the above developed theory. 
