AND SOME ANALOGOUS RAYS. 
479 
yielded a slightly larger shadow than when cold. But this could not be determined 
with certainty. 
5. Attem'pts to Concentrate Cathode Ii,ays, 
The concentration of cathode rays by the use of concave cathodes to focus the beam 
dates from the classic researches of Crookes."^' In the experiments now made it was 
sought to concentrate the rays by other means. The first of these means was 
reflexion from the surface of a non-conductor—glass—at a small grazing angle. A 
tube [No. G 20], (fig. 13), was prepared, within which was suspended by platinum 
links an inner funnel of glass, about 47 millims. long, having an internal diameter 
of 12 millims. at the larger, and 8 millims. at the smaller end. The suspension 
permitted the funnel to be swung aside by tilting the tube. This tube was exhausted 
to the point at which Bontgen rays are but just emitted, the emission ceasing when 
the tube was warmed. To the eye there was no apparent difference in the brightness 
of the yellow-green luminescence of the anticathodal end of the tube whether the 
funnel were present or absent. The funnel itself cast a broad annular shadow, but it 
produced no difference in the brightness of the central patch within. On examining, 
by the aid of luminescible screens of platinocyanide of barium or of scheelite, the 
emission of Bontgen rays from this central patch, no difference was perceptible in 
the luminosity, whether the funnel was absent or present. It did not concentrate 
the cathode rays. 
* ‘ Phil. Trans.,’ Part I., 1879, p. 142. 
