374 Prof. E. Goldstein on 
The S r rays are also closely related to the K^-rays. For 
if the luminosity of the S r rays is different over different 
portions of the cathode — a result which may, for example, 
be produced by the approach of a magnet — the luminosity of 
the Kj-rays emitted from the corresponding portions of the 
cathode surface varies in a similar manner. 
There arises the problem of the true origin of the canal 
rays. 
That the canal rays produced at the back surface of 
the cathode have their origin at the front surface is rendered 
very probable by the already established fact * that the 
direction of the individual pencils is determined very largely 
by the shape of the front surface of the cathode, but appears 
independent of the shape of the back surface. If the latter 
is plane, e. </., the canal rays are convergent if the front 
surface is convex, and become divergent if the front surface 
is made concave. 
As regards the origin of the canal rays, it appears to me 
that the part played by the openings has hitherto not received 
sufficient attention. 
In using slotted plates of not too great a thickness for the 
production of canal rays, we must regard not so much the 
entire plates as the walls of the openings — e. r/., the opposite 
sides of a slit — as forming the cathodes ; these, along with 
the edges bounding the openings, are effective in the pro- 
duction of canal rays, and it is incorrect to regard the 
openings in general as merely forming so many neutral 
channels of escape. 
There further seems to me to be a close connexion between 
the canal rays and a form of radiation which is also obtainable 
with plane, not perforated cathodes, and which forms rays 
both tangential to the cathode plane and moderately inclined 
to it, which pass inwards over the cathode from one of its 
edges to the opposing edge and then into free space. In the 
case of a circular plate, these rays obviously only produce a 
uniform glow around the plate. But if the plate be cut 
Fio-. 1. 
away in several places along chords (fig. 1), the rays which 
start from these chords may be recognized — in hydrogen, 
* E. Goldstein, Sitzungsber. d. k. Akad. d. li'issensch. zn Berlin, 1886, 
p. 095; Wied. Ann. lxiv. p. 43 (1898). 
