472 
DR. S. P. THOMPSOX ON CATHODE RAYS 
C were projected upon the tube-walls. As is usual in such tubes, these shadows 
were quite well defined and were surrounded by the usual margin of brighter 
luminescence. When B and C were made cathodes, while X was made anode, each 
cathode was observed to produce an oval luminescent patch upon the tube-wall 
around its OAvn region. When B and C were both made anodes, being connected 
together by an external wire, their shadows were both quite small and narrow, 
considerably less than the geometric shadow, being only about 6 millims. long and 
1 millim. broad. Nor were they rectangular in shape (fig. 2), but somewhat tapered 
to a point; and be 3 mnd the tip of each appeared a more luminous point in the 
splashing luminescence on the glass wall. If B was alone anode, while C was 
disconnected, the shadow of C Avas full-size, and of nearly rectangular shape ; while 
the shadow of B (the anode) was someAvhat smaller, and showed at its end a 
flickering luminous spot at h (fig, 3). 
Fig. 1. Fig. 2. Fig. 3. 
When B was connected to A so that both A and B were cathodes, C being anode, 
the shadow of B swelled out to an oval shape, some 22 millims. long and 18 millims. 
Avide. The shadow of C Avas enlarged similarly if B Avas made anode, and C joined 
to A as cathode. The size of this oval shadoAv Avas found to depend on the nature of 
the connexion to the cathode. By introducing a bad conductor, such as a piece 
of dam]^ AA^ood or a highly exhausted A'acuum tube into the conducting line, between 
the cathode and the electrode casting the sho.doAv, the size of the shadoAv could 
be Auiried from normal dimensions up to the full oval. When either B or C AAms 
thus made cathode, the anode shadow shrank up altogether and disappeared, though 
the luminous spot at c or h remained. 
When A Avas made anode, and B and C both cathodes, each Avas, as remarked 
above, surrounded by an oval luminous patch on the glass AA^all; which patch was 
brighter than the rest of the surface of the bulb, and AA^as outlined AAdth a still 
brighter marginal line. If B Avas disconnected, or its continuity Avith the cathode 
impaired by introducing a bad conductor, the patch surrounding it shrank, AA’hile 
that surrounding C expanded. If B was joined to the anode the patch surrounding 
it disappeared. When, as in fig. 4, B and C w'erc joined through a rod of avoocI, to 
Avhich the cathode Avire from the coil Avas brought, the sizes of the Iavo patches could 
