16 On Radiant Matter. 



the screen. In this pear-shaped bulb (Fig. 9) the nega- 

 tive pole (a) is at the pointed end. In the middle is a 



FIG. g 



cross (6) cut out of sheet aluminium, so that the rays 

 from the negative pole projected along the tube will be 

 partly intercepted by the aluminium cross, and will project 

 an image of it on the hemispherical end of the tube which 

 is phosphorescent. I turn on the coil, and you will all 

 see the black shadow of the cross on the luminous end of 

 the bulb (c, d). Now, the Radiant Matter from the nega- 

 tive pole has been passing by the side cf the aluminium 

 cross to produce the shadow; the glass has been ham- 

 mered and bombarded till it is appreciably warm, and at 

 the same time anothei effect has been produced on the 

 glass its sensibility has been deadened. The glass has 

 got tired, if I may use the expression, by the enforced 

 phosphorescence. A change has been produced by this 

 molecular bombardment which will prevent the glass 

 from responding easily to additional excitement ; but the 

 part that the shadow has fallen on is not tired it has not 

 been phosphorescing at all and is perfectly fresh ; therefore 

 if I throw down this cross, I can easily do so by giving 

 the apparatus a slight jerk, for it has been most ingeniously 

 constructed with a hinge by Mr. Gimingham, and so allow 

 the rays from the negative pole to fall uninterruptedly on to 

 the end of the bulb, you will suddenly see the black cross (c, d, 

 Fig. 10) change to a luminous one (e, /), because the back- 

 ground is now only capable of faintly phosphorescing, whilst 

 the part which had the black shadow on it retains its full 

 phosphorescent power. The stencilled image of the lu- 

 minous cross unfortunately soon dies out. After a period 



