On the Canal-Ray Group. 373 
may be observed in the case of perforated or entire cathodes 
when the ordinary cathode rays are deflected to one side by 
a magnet. They spread, in the case of a cathode which com- 
pletely fills the opening of the tube, not backwards, but 
towards the anode. Towards magnets and electrostatic fields 
they are not more sensitive than the true canal rays. In 
hydrogen they appear rosy, in air golden-yellow (cf. below j. 
They excite luminescence in sodium, lithium, and magnesium. 
Like the canal rays, they are propagated in straight lines, 
but in the case of a plane plate form a moderately divergent 
pencil, and in general closely follow the direction of the 
ordinary cathode rays which start from the same surface 
and are not influenced by external forces. Their direction 
relatively to the cathode, as well as the side towards which 
they are propagated, is indicated by the shape and position 
of the shadows cast by solids placed in their path*, in 
what follows they are briefly termed K : -ravs f. 
The first layer of the cathode glow, whose behaviour I 
have recently described in detail J, exhibits similarities and 
close relationship with the canal rays, so much so that one 
might be led to suppose that the canal rays are identical with 
the first layer of the cathode glow, and are merely that 
portion of it which passes unaltered through the openings in 
the cathode. 
Contrary to this supposition, it has been found § that the 
first layer consists of rays which are extraordinarily suscep- 
tible to influences that affect canal rays but slightly. This 
seems to exclude the possibility of a complete identity of the 
two. The rays of the first layer will be referred to in what 
follows as S x-rays. 
* E. Goldstein, Verhandl. d. Deutscken Physik. Gesellscli. iii. p. 207 
(1901). 
t [jSot-E, Jan. 30th, 1908.] — The K x -rays have first been described in 
my earliest paper on canal rays (Sitzwiysbei'. d. K. Ahad. d. Wissensch. zu, 
Berlin, 1886). where on p. 698 it is shown that rays of the same colour 
and the same magnetic behaviour as canal rays proper are emitted also 
by non-perforated cathode-disks standing; in the free gas-space, and are 
found in front of the cathode. In 1901 t described the following- expe- 
riment ( Verhandl. d. Deutsch. Physik. Gesellsch. iii. p. 207) : — " As 
cathode in a tube of about 4 cms. width a nickel disk of 5-10 mm. is 
used and a wire or a glass rod of some millimetres thickness is fixed for 
casting a shadow. Evacuating the ^ hydrogen) gas to a proper degree 
and bending the ordinary cathodic rays to the side by a magnet, one will 
observe that the rosy canal-rays form a continuous mass of light tilling 
the width of the tube, while behi/id the object is lying a sharply-bounded 
weakly divergent shadow-space. Undoubtedly we see here i-ays with 
qualities of canal rays, extending cncay from the cathode." 
+ E. Goldstein, I.'c. iv. p. 64 (1902). 
§ E. Goldstein. /. c. iv. p. 64 et seq. (1902). 
