Reflection of Electrical Rays. 453 



luminosity as before — a proof that this luminosity does not 

 depend upon optical reflection. So also the phosphorescence 

 produced by diffuse reflection remains unaffected if P be con- 

 structed of some material which does not phosphoresce at all. 

 It is further a matter of indifference whether P is metallic or 

 consists of an insulator. In the former case P may even be 

 made the anode of the discharge, without the reflection of the 

 rays appearing in any way weakened. 



The kathode-rays are therefore not absorbed by the anode, 

 even when they play directly upon the surface of the anode. 

 Further we see, as already mentioned above, that the pheno- 

 menon in question cannot be explained by supposing that the 

 surface struck by the direct kathode-rays is itself converted 

 into a kathode. 



If we bring small objects between the plate P and the phos- 

 phorescent surface of Z, such, for example, as the wire D 

 (fig. 6), whose distance from P can be varied by rotation 

 round the axis D, we can very well recognize the character of 

 the diffuse reflection which the place s causes in the rays 

 which fall directly upon it. For the shadow of the wire D 

 only appears narrow and sharp when the wire is brought close 

 to the wall of the vessel; if D is moved from the wall towards 

 P, its shadow soon becomes bread and indistinct. If we cut 

 off a further portion of the kathode-rays, by means of a small 

 movable plate of mica introduced into Z at the mouth of r 3 

 the space s, directly impinged upon by the rays, of course 

 becomes smaller. The further this decrease proceeds the nar- 

 rower and sharper does the shadow of D become, exactly as 

 we should expect on the theory of diffuse -reflection. 



I will here cite only one other consequence of this theory 

 which has been experimentally verified. I may take it as 

 known that a pencil of rays emitted by a plane kathode after 

 it has passed, as in fig. 7, through the aperture (supposed cir- 

 cular) of a diaphragm occupying the whole area of the tube, 

 gives on the flat wall W a well-defined circular luminous 

 figure on a dark ground. 



Upon our assumption of the diffusion of the kathode-rays, 

 this ought not to happen any more if the rays are made to 

 pass through a cylindrical tube open at both ends (fig. 8), in 

 place of the thin diaphragm. For since the different rays of a 

 plane kathode are not altogether parallel to each other, but also 

 diverge somewhat around the central portion of the kathode, 

 a part of them must play upon the wall of the tube r, and be 

 then diffusely reflected. The portion of the diffuse rays which 

 reach C must then form an extended luminous space round 

 the bright surface resulting from the direct rays. We find 



