92 Prof. E. Wiedemann on the 



8. Further Observations upon the Influence of the Magnet upon 

 the Discharge. — A series of measurements and observations 

 were made upon the behaviour of the discharge under the influ- 

 ence of feeble magnets. These have led to results which partly 

 differ from those of previous observers, partly complete them. 



I employed for these experiments a tube 25 millim. wide 

 and 410 millim. long, with plate-electrodes which had been 

 highly exhausted. 



The kathode k (fig. 3) was insulated and connected with the 

 negative pole; the electrode a, on the other hand, was con- 

 nected with the earth by a long moist thread, as well as to the 

 positive pole of the machine. A dark space appeared about 

 k, which extended to b; this was traversed by the kathode- 

 rays, which issued in a narrow, slightly divergent pencil from 

 the centre of the plate h. Up to the middle of the space h b 

 these were of a white colour; but afterwards more of a blue 

 colour. From b itself issued from the whole surface of 

 the corresponding kathode-layer a bluish luminosity — the 

 "glow-rays," through which the kathode-rays could be traced. 

 Three or four cloudy stratifications were visible about a. The 

 tube showed from b to a a bright-green light on the walls, 

 so that here also the peculiar kathode-rays penetrate the posi- 

 sitive light without meeting with any hindrance whatever, 

 and the positive light can also diffuse itself through the 

 kathode-rays unhindered. If the one pole of a bar-magnet be 

 brought near such a tube, green light becomes visible on the 

 wall, which shows that the kathode-rays and the blue " glow- 

 light " are, as we know, so deflected that a north pole placed 

 under the tube throws them to the right, if we are looking 

 from the positive electrode towards the negative. 



But these phenomena are seen still more clearly if, instead 

 of a bar-magnet, we employ a horseshoe-magnet with poles as 

 close to each other as possible (best a small lamellar magnet 

 of Jamin's construction), placing it so that the tube occupies 

 the equatorial position. 



We must distinguish two cases: — (1) Both poles of the 

 magnet produce a deflection of the discharge, such that the 

 " glow-light " and the kathode-rays are deflected on each side 

 towards the walls; or (2) both poles deflect the rays towards 

 the centre of the tube. 



(1) In the first case, if the magnet is placed between the 

 anode and the boundary of the dark space, there is seen on the 

 w T all a green spot of light bounded by two ellipses. These 

 ellipses are produced by planes intersecting the tube and in- 

 clined to its axis. The form is that represented in fig. 10; c 

 is the luminous surface, af and b d its boundaries. The boun- 



