AND SOME ANALOGOUS RAYS. 
481 
when C is made cathode. It is immaterial whether B or A serves as anode, or 
whether an anode in a bulb in the exhausting-tube is used. The shape and position 
01 this shadow, which is dark against the yellow-green luminescence of the tube-wall, 
indicate distinctly that it is cast by rays proceeding from A. This quasi-cathodic 
shadow is cast by rays proceeding from A, even when A is anode, and under con¬ 
ditions which preclude the possibility of an oscillatory discharge. No shadow is 
pioduced if the cone of cathode rays proceeding from C is diverted by the influence 
a external magnet from falling on the anticathode A. It is therefore clearly due 
either to cathode rays reflected at A, or to some other rays, resembling cathode rays, 
which are originated at A under the impact of the cathode rays from C.* Specular 
reflexion of cathode rays is not known to exist, and has not been observed in any of 
these tubes. No trace is seen of any blue cone or beam that might be a geometrical 
jnolongation of the reflected cathode cone or beam. If reflexion is here operative, it 
is diffuse, not specular. But if specular, it differs from ordinary specular reflexion in 
two lespects : (1) the shadows have no penumbra but are sharply defined, even 
though the anticathode surface is relatively large ; (2) the distribution of the rays 
differs from that of ordinary specular reflexion. 
Fig. 16. 
Fig. 17. 
The shadow of B thus thrown on the tube-wall at^i can be observed at a degree of 
exhaustion quite msufficient to excite Eontgen rays ; it can also be observed up to 
the highest exhaustion. like the shadow of ordinary cathode rays, it’can be deflected 
by a magnet placed over the tube between the object and the tube-end. It is also 
suscepBble to electrostatic deflexion; the shadow expanding when B is made 
cathodic, contracting slightly when made anodic. The colour of the luminescence 
of the glass undei the impact of these rays is identical with that produced b}^ 
ordinary cathode rays. 
If, now, a luminescible screen of platino-cyanide of barium, or one of scheelite, is 
* This conclusion was reached by Wiedemann and Ebeet as the result of experiments yet unpublished. 
See their paper “ Ueber elektrische Entladungen,” in the ‘ Silzungsberichte der Physikal.-med. Societat 
zu Erlangen,’ December 14, 1891. 
VOL. CXC.— 
3 Q 
A. 
