382 Prof. E. Goldstein on 
It seems permissible to suppose that these diffuse rays stand 
in the same relation to the canal rays proper and to the regular 
nebulous rays, as does the light of the third layer of the 
ordinary cathode glow to the regular, ordinary cathode rays — 
L e., that the diffuse rays are due to the impact of the canal rays 
proper 8fc. apainst the particles of the c/as *. 
The diffuse golden-yellow rays play an important part in 
investigations relating to the canal-ray group. To their 
existence is due the impression that the canal rays proper 
themselves emit golden-yellow light. In reality, the light 
of the canal rays proper is bluish, and it is only the strong 
diffusion that envelops them in a golden-yellow light which 
to a large extent obscures the bluish one. To the same cause 
is to be ascribed the apparently intense chamois to golden- 
yellow colour of the similarly bluish rays of the first layer in 
air. It is only at very low pressures, at which diffusion 
becomes small, that the bluish colour appears more clearly. 
If by means of an anode fixed in the neighbourhood of the 
cathode a shadow be produced in the S L -rays, this shadow is 
also, at moderate pressures, not entirely destitute of light, 
being filled with the diffuse golden-yellow light. This same 
light also fills the shadow cast in K^-rays when the pres- 
sure is not very low. It seems that the K^-ravs, and also 
the nebulous rays enveloping the canal rays, are bluish in air, 
and only owe their golden-yellow appearance to the admixture 
of the diffuse rays. 
Even in the case of double cathodes (squares, pentagons, <fec.) 
arranged in free space, a closer investigation shows that 
the (in hydrogen) rosy arms of the cross- and star-shaped 
figures form the most prominent, it is true, but not the only 
kind of rosy light that is related to the canal rays- The 
bright narrow arms (when viewed in the direction of the axis 
of the plates) are, as a matter of fact, seen to lie between 
very feebly illuminated wide fields of rosy light. Shadow- 
casting objects show that this light is also propagated (away 
from the cathode) strictly along straight lines, and that it arises 
from every part of the space between two parallel sides (of the 
polygonal cathodes), in the form of wide fans — strongly 
* [Note, Jan. 30th, 1908.] — In a lately published paper Prof. J. J. 
Thomson (Phil. Mag. [61 vol. xiv. p. 359, 1907) declares to have "found 
that positive rays are to be found in all parts of the tube which have an 
uninterrupted view of the ordinary ' Canalstrahlen,' or of that luminous 
patch next the cathode of which the Canalstranlen are the prolongations." 
Rays of a peculiar intensity are observed by Prof. Thomson " right in 
front of the cathode." — It seems that my above statements published 
previously on the diffuse rays and on the E^-rays have escaped Prof. 
Thomson's attention. 
