the Canal-Ray Group, 375 
e. </.. as narrow rosy pencils which pass from the fudges 
lying opposite the chords in a radial direction into space *. 
The luminosity o£ these pencils is comparatively feeble, and 
hence not easily noticeable : it may, however, be greatly 
increased by arranging two such congruent cathode plates 
coaxially at a distance of a few millimetres apart. The 
luminosity is then not merely doubled, but increased many 
times. The reasons for this increase of luminosity will be 
investigated elsewhere. If in a spherical tube (8-11 cms. in 
diameter) there be fixed facing each other two small con- 
gruent squares (side = 8 mm.) with their sides parallel, then 
in (hydrogen) gas at a suitable pressure there may be seen 
a bright cross (fig. 2) whose luminous arms, of a rosy colour, 
Fig. 2. Fig. 8.. 
proceed from those portions of the space between the two 
squares corresponding to the middle portions of the sides. 
If the cathode consists of a pair of regular pentagons, there 
is produced a five-rayed star, whose five arms, however, do 
not arise from the middle points of the sides, but from the 
angular points of the space between the plates (fig. 3). 
In the case of a pair of regular hexagons, there appears a 
six-rayed star whose rays again appear to arise from the 
middle points of the sides t- In general, in the case of even- 
sided regular polygons, the star-shaped figure is formed by 
* E. Goldstein, Physik. Zeitschr. i. p. 133 (1899). 
+ In order to cany out these experiments, we may place two polygonal 
plates facing each other, and either provide them with separate leading- 
ill wires (attached to their back surfaces or edges), or else make use of a 
single leading-in wire, the connexion between the two plates beino- 
established by means of a thin rod fixed to suitable points 
