482 



Cathode Rays and some analogous Rays. 



to whether it is a conductor or not. Objects protected by a non- 

 conducting layer of glass do not at moderately low exhaustions, 

 when made cathodic, repel or deflect cathode rays, and their shadow 

 does not enlarge. But at a certain minimum exhaustion they sud- 

 denly exert an electrostatic deflection. Naked objects made cathodic 

 deflect the cathode rays at all exhaustions. 



3. The " splash " phenomenon often observed on the tube-wall of a 

 Crookes' tube, where it is struck by the cathode beam, at the stage 

 of exhaustion a little below that which suffices to evoke Ront^en's 

 rays is due to electrostatic deflections of the cathode rays by the 

 charges on the glass. 



4. A hot wire used as an object casts a cathodic shadow precisely 

 like that of the same wire cold. Under some circumstances, if the 

 wire is heated by an electric current, the difference between the 

 electrostatic state of its different parts may slightly affect the size of 

 the shadow it casts. 



5. Cathode rays cannot be concentrated by reflection either from a 

 non-conducting or a conducting surface, nor by passage through a 

 metal tube which is itself negatively electrified. 



6. When cathode rays strike upon an internal metal target or anti- 

 cathode there are emitted from the latter (both at exhaustions lower 

 than suffice to produce Rontgen rays, and at exhaustions at which 

 those rays are also produced) some internal rays resembling ordi- 

 nary cathode rays in the following respects : — They produce a 

 similar luminescence of the glass : they cast shadows of objects ; they 

 are susceptible of deflection both magnetically and electrostatically. 

 But they produce no Rontgen rays where they fall upon the glass 

 surface. They do not follow either the law of specular reflection, 

 nor that of diffuse reflection, but are emitted from the anti-cathode 

 surface apparently according to a similarly anomalous distribution 

 to Rontgen's rays, i.e., with nearly equal intensity, at all angles up 

 to 90° wdth the normal. It is proposed to call these rays para-cathodic 

 rays in contradistinction to the ordinary or ortho-cathodic rays. 

 From the similarity of their distribution with that of the Rontgen 

 rays it is inferred that the physical processes concerned in their 

 production are identical. These para-cathodic rays are emitted 

 from the anti-cathode both when the latter is made an anode, and 

 when it is neutral or even made cathodic. From an anti-cathode 

 there may proceed at one and the same time, and in one and the 

 same direction, para-cathodic rays and Rontgen rays, which, meeting 

 an interposed object, may cast simultaneously two shadows — a para- 

 cathodic shadow on the glass, and a Rontgen shadow on an external 

 screen of barium platinocyanide. The former shadow can be deflected 

 by a magnet, the latter cannot. The former shadow expands if the 

 object is made cathodic; the latter does not. 



