AND SOME ANALOGOUS RAUS. 
489 
paragraphs as casually occurring. This phenomenon is a second species of 
fluorescence of the glass, and is always produced, provided the exhaustion be 
sufficiently high, when a cathode beam is directed against glass through a thin 
screen or through an aperture in a metallic screen which is itself made cathodic. 
This second fluorescence was examined with the spectroscope, when its light was 
found to consist simply of the D-lines of sodium. 
The effect of an external magnet upon this tube was remarkable. When the 
horse-shoe was placed vertically, with its poles on either side, over the tube between 
the cathode and the helix, the yellow-green luminescence on the glass was driven 
into two portions ; one, apparently due to rays proceeding from the cathode proper, 
being deflected up to the upper side of the tube ; the other, apparently due to rays 
jji’oceeding from the near end of the helix, being deflected down to the lower side 
of the tube. Or, on reversing the poles of the magnet, these deflexions were 
reversed. But in each case the blue cone proceeding from the far end of the helix 
appeared to be slightly deflected downwards. When the magnet was, however, 
brought down over the further j^art of the tube, so that its poles were one on each 
side of the tube, with the blue cone of rays between, the cone of rays was absolutely 
unaffected. That these rays were really rays of some kind was proved by the 
circumstance that they could cast shadows. A scrap of glass which accidentally 
remained inside the tube was observed to cast a shadow behind itself, none of the 
tawny fluorescence appearing in the shadowed portion. 
To investigate the j^henomenon further, tube [No. C 11], (fig. 20), was then inade. 
Opposite the cathode there was introduced a screen of iron wire gauze, mounted upon 
Fig. 20. 
a platinum terminal, T, which passed through the glass. Between this screen and 
the tube-end was inserted a vertical wire, W, as an object to cast a shadow. If the 
gauze screen was made anode, or was left neutral, the usual sharp shadow of it was 
cast on the tube-wall by the {ortho-)cathodic rays, the whole tube being lit up with 
yellow-green fluorescence except where the lines of shadow fell. When the gauze 
screen was made cathodic that part only of the tube vffiich was between the cathode 
VOL. cxc. —A. 3 R 
