490 
OX CATHODE RAYS AXD SOIIE ANALOGOUS RAYS. 
and the screen showed the yellow-green tint, but, beyond the screen, there was the 
blue cone of rays, producing on the remainder of the tube the second, or dark-orano-e 
fluorescence, as before, and in this second fluorescence the shadow of the wire could 
be seen upon the glass. This shadow was not displaced by a magnet held over the 
blue cone; it was, however, displaced if the ma,gnet was held over the tube at the 
part where the yellow-green fluorescence showed itself between the cathode and the 
screen. The rays of this blue cone did not appear to be electrostatically sensitive, 
since the size of the shadow of the wire was not affected by electrifying the wire. 
Another feature which had been noticed with the preceding tube, but was exceeding!}- 
striking in the present one, was the difference in the situation of the two kinds of 
fluorescence. In the present tube, with its thin gauze screen, the two kinds of 
fluorescence met in the plane of the screen, and it was evident that while the 
fluorescence of the second, or dark-orange, kind was exactly confined to the inner 
surface of the glass, the fluorescence of the first, or yellow-green, kind was not so 
confined, but extended right through the glass. This seemed at first to be an optical 
illusion, but careful scrutiny proved it to be really so. It is most sugo-estive to find 
from spectroscopic evidence that both kinds of fluorescence are referable to the same 
element—the sodium of the glass employed. The circumstance that the rays last 
described should excite the emission of light giving a spectrum of so totally different 
a character, is itself sufficient to justify their being considered as different from the 
ordinary cathode rays. It is, therefore, proposed to distinguish them by the name 
dia-cathodic rays. 
These observations may be summed up as follows ;— 
(1.) When cathode rays fall upon a perforated metcdlic screen, which is itself made 
cathodic, or upon a tubular cathode, there emerge beyond the latter some rays, here 
termed dia-cathodic, ivhich are incapable of exciting the ordinary cathodo-luniinescence. 
(2.) These dia-cathodic rays are not themselves directly defected by a magnet. 
(3.) They are capcdole of exciting a different hind of luminescence, the luminescent 
surface emitting light which, in the case of sodium glass, shows a gas spectrum, 
(4.) They can cast shadows of intervening objects. 
[Note added November 7, 1897 —Recent furtber examination of the ray.s, here termed diacathodic, 
has shown me that they are very similar in their properties to, if not identical with, the “ Kanal- 
strahlen,” which Goldstein has found to be projected backward from cathodes I have not yet been 
able to determine whether these diacathodic rays always accompany the ortho-cathodic rays or not. 
Observations on the yellow-green fluorescence of the first kind, made through revolving slits or in a 
rotating mirror, show that its colour changes before it dies away, becoming orange. This may be due 
to fatigue, however, and not to the greater jaersistence of emission of a different kind of ray.—S.P.T.] 
