480 
DR. S. P. THOMPSON ON CATHODE RATS 
In the experiments made with tube [No. G 17], (fig. 9), described above, when the 
two external coatings of foil were made cathodic, no increase of brightness had been 
observed in the patch of luminosity on the end of the bulb, in spite of the narrowing 
of the luminous space between the two lateral shadows. 
A tube [No. C 24], (fig. 14), was constructed, having a fiat cathode, K, opposite to 
which was inserted obliquely, as an anticathode, a concave cup, C, of aluminium. A 
third electrode, A—an aluminium wire—was inserted at the further end of the bulb 
as anode. The cathode discharge was directed agamst this concave anticathode, at 
various degrees of exhaustion up to the highest when no spark could be sent through 
the tube. At no stage, however, was there any appearance, either by internal cones 
of rays, or by any special spot of luminescence on the glass wall, or by the evidence 
of a luminescible screen applied outside, of any concentration by the concave anti¬ 
cathode of rays of any kind. 
Another tube [No, C 9], (fig. 15), was constructed, having an internal cylindrical 
tube of silver supported at each end by three j)rojecting feet. This was not found to 
concentrate cathode rays that were passed along its axis. When it was itself made 
anodic its shadow was more sharply defined. But, when it was made cathodic, so far 
from any concentration being produced on the cathode rays directed along its axis, 
there appeared a new set of phenomena which are described below in § 8. 
Another attempt to concentrate the rays by passing them along the axis of a helix 
of iron wire within the bulb, while a current traversing the wire produced a longi¬ 
tudinal magnetic field, is also narrated below. It also failed to produce any concen¬ 
tration of the cathode rays. 
6, Comparison of Cathode Shadows ivith Kontgen Shadoivs. Production of 
Internal or Paracathodic Pays. 
In order to be able to compare together ordinary cathode shadows and the 
shadows produced on external luminescent screens by Eontgen rays a number of 
tubes were constructed, having v/ires or other objects introduced for the purpose 
of casting shadows. One of these tubes was described at the meeting of the British 
Association at Liverpool.* A somewhat simpler tube [No. M 12] is depicted in 
fig. 16. It consists of a pear-shaped bulb having a concave cathode, C, focussing upon 
an oblique anticathode,t A, at its upper end. A lateral tube into wdiich the upper 
end of the pear-shaped bulb is united has an aluminium wire, B, inserted as an object 
to cast shadows. This aluminium wire, about 3 inillims. in diameter and 17 millims. 
long, is mounted upon a platinum wire fused in through the tube-wall. 
At fairly low degrees of exhaustion the wire B casts a shadow upon the tube-end 
* ‘ British Association Report,’ 1896. See also ‘ Electrical Review,’ p. 417, September 25, and p. 432, 
October 2, 1896. 
+ The term anticathode signifies an object upon which cathode rays are directed, as against a target. 
See ‘ Nature,’ March 12, 1896, p. 437. 
