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XXXVI. On the Canal-Fa y Group. By E. Goldstein*. 
IT is permissible to speak of" a tk canal-ray group," in so 
far as there exist — as will be shown — several forms of 
radiation which have certain characteristic features in common 
with each other and with the canal rays properly so called, 
while in other respects they exhibit differences of behaviour. 
By true canal rays we mean those which arise on the side 
away from the anode, at a cathode completely filling the 
opening of the tube and provided with small perforations or 
narrow slits, and which in the case of holes form narrow 
cones, and in the case of slits beams of slight divergence. 
Although it is to be surmised that eventually it will be found 
possible to consider the various members of this group of 
radiations from a common standpoint, and to reduce their 
differences to a quantitative gradation, I am nevertheless of 
opinion that, in the interests of further investigation, it is 
advantageous, in describing the various members, not to 
group them together as yet, but to bear in mind their dif- 
ferences as well as their similarities. 
The true canal rays on leaving the cathode openings 
proceed in straight lines, and, in the case of a cathode com- 
pletely filling the tube, towards the side away from the 
anode; they are not appreciably deflected by weak magnetic 
or electrostatic fields. In the case of a plane parallel plate, 
perforated with a number of holes or slits, the various pencils 
in general converge towards each other and towards the axis 
of the plate. Their colour is rosy in hydrogen, bluish in air 
or nitrogen f. At the glass wall, and in general in any 
compounds containing sodium, they excite golden-yellow 
light ; in compounds containing lithium the excited light is 
red, and in magnesium compounds green. In all these cases, 
the line spectrum of the metal is observed. 
Closely allied to the canal rays proper are the rays which 
* Communicated by the Author from the Verhandl. d. Devtsch. Physik. 
Geselhch. iv. p. 228 (1902). 
[Note, Jan. 30th, 1908.]— I am greatly indebted to the Editors of the 
Philosophical Magazine for reprinting- the above paper which was pub- 
lished first in the Verhandl. d. Deutsch. Physik. Geselhch. nearly six years 
ago. It contains a condensed summary of many years' observations con- 
cerning canal rays since my first publication (1886) on this subject. As 
far as may be judged from recent literature, my observations do not 
appear to have been of much use hitherto. I would consider it an 
advantage if the above reproduction would prove to the reader that 
canal rays are a much more complicated phenomenon than generally 
admitted. — E. G. 
f The common impression that canal rays are golden-yellow in air is 
based on the effect produced by a form of radiation discussed below. 
