70 Electric Discharges in Rarefied Gases. 



Again, using a tube with the cathode in the centre, the anode 

 at one end, the cathode being pierced with one or more small 

 holes, Goldstein found that the front side of the cathode shows 

 the usual cathode light. From the back of the cathode rise 

 high columns of reddish-yellow light, the blue rays being 

 entirely absent. These were called " Canal Rays." It seems 

 to me proved that they are identical with the luminous glow 

 on the front of the cathode, and that both are produced by 

 positive ions travelling from the anode to the cathode, and, if 

 the cathode is pierced, some pass through and produce the 

 canal rays. Wien showed that they carried with them a posi- 

 tive charge. An object, placed in the dark space in front of 

 the cathode, throws a shadow on the cathode, as if it protected 

 the cathode from the impact of particles striking it normally. 

 If holes are pierced in the cathode in this shadow no canal rays 

 appear there. Metals placed in the path of the rays become 

 oxidised, so that if an object be placed in the dark space in 

 front of a cathode, consisting of wire gauze and a polished metal 

 plate placed behind it, we have on the plate an image produced 

 of the object placed in front of the cathode. If now a luminous 

 screen be placed in front of the cathode, we have a shadow of 

 the object again produced, which is larger than the object if 

 this latter is inside the cathode dark space, and about the same 

 size if outside, so that cathode rays only come from the parts 

 struck by these anode ions. 



In the simple case of the discharge passing as a thin line of 

 reddish light, we may describe the effect of a magnet by saying 

 that the displacement of the discharge is like that of a perfectly 

 flexible wire carrying a current. *' If a magnet be applied to a 

 striated column, each striae is subjected to a rotation or deform- 

 ation, as if the striae marked the termination of flexible currents 

 radiating fiom the bright head of the striae behind it, and ter- 

 minating in the hazy inner surface of the striae in question." 



The negative glow behaves in a magnetic field, like a 

 magnetic substance without weight, and perfectly free to move. 

 The magnetic effect on the cathode rays may be expressed by 



