677 
The said experiments were executed by means of two very thin 
muscovite-lamellae, about 0,22 m.m. thick, which were obtained by 
cleavage from one and the same crystal, and which could be crossed 
with respect to each other at arbitrarily variable angles y. In all 
cases, in which the angles + were varied between O° and 60°, the 
RONTGENOgrams obtained appeared to be almost the complete super- 
positions of the images of the composing thin lamellae. From tbis 
result it became more and more probable, that the images formerly 
obtained might finally appear to be also such superpositions. For the 
purpose of investigating this more in detail, a negative was prepared 
from the original image of a single lamella, as reproduced in Fig. 1 of 
the Plate, and from this a number of equal diapositives were made 
on pieces of photographic film. These film-diapositives were now 
carefully piled-up at the angles p with respect to each other, in the 
same way as the lamellae in the mica-piles used formerly. The thus 
obtained combination was carefully compared in transmitted light 
with the original photos formerly obtained. Although some spots 
of the primary images did not coincide completely with other spots, 
also in these cases their mutual distances might be considered small 
enough to give together the final impression of one spot of greater 
intensity. If this be taken into account, the combined image is 
really in its principal features analogous to the photographic image 
of the mica-pile. However, there are certain deviations: some spots 
were lacking in the last photographs, which were visible in the 
film-image with rather great intensity; some spots were feebler than 
in the film-image, and generally the relative intensities of the spots 
were different from those in the image of the combined films. 
Partially, these deviations could be easily explained by the influ- 
ence of a selectwe absorption of some wave-lengths, as already stated 
in former cases, when the rays of the tungsten-anticathode of the 
Coolidge-tube pass through thicker layers of the crystalline medium. 
With the aid of a muscovite-crystal of 2,35 m.m. thickness it was 
possible, indeed, to prove that certain spots in the diffraction-image 
obtained with it, — e.g. the spot in the middle of the first circular 
row beneath the centre of Fig. 1 of the Plate, — were convin- 
cingly less intense than the corresponding spots in the image 
obtained with a 0,22 m.m. thick lamella of the same crystal; and 
exactly in those places also the spots were absent in the composed 
image of a mica-pile of circa 3,5 m.m. thickness. By intentional 
experiments, in which the time of exposure was regulated in such 
a way, that the influence of solarisation-phenomena of the most 
intensive spots was certainly excluded, it could be proved 
44* 
