under the Influence of the Electric Discharge. 411 



by the current, but at points where blind branch tubes are 

 placed, as, for example, in the pieces joined on for the purpose 

 of securing the joints (PL IX. fig. 6). 



2. It was further examined whether the negative discharges 

 which excite the green light, the so-called kathode-rays, do 

 really propagate themselves only in straight lines. For this 

 purpose the apparatus fig. 11 was employed. If a was negative 

 and b positive, the discharge from a struck first upon the 

 glass wall at s, causing it to shine brightly, and then upon 

 the bend at m (when the angle at m was about 30°), where 

 bright green light also appeared. On the other hand, the tube 

 was only feebly illuminated from s to m and m to I ; whilst 

 on the surface d, exactly opposite the mouth of the tube s m I, 

 there appeared a bright green spot, in the midst of which there 

 was a sharp shadow of the electrode e. 



That this spot of light is not produced by light which has 

 undergone several reflections in the interior of the tube s m I 

 may be seen in two ways : first, there was no violet spot when 

 the positive discharge traversed the tube without the pro- 

 duction of green light ; and, further, the green spot alters its 

 position under the influence of a magnet. 



If the angle at m is chosen greater than 45°, and, moreover, 

 the tube m Z is taken tolerably long, the spot is at first faint, 

 but appears with greater brilliancy as soon as the part of the 

 tube surrounding a is touched directly with the finger. At 

 the same time the discharge issuing from a within a s is hardly 

 affected by the magnet. Touching a point at some distance 

 from a is without influence. 



Whether we have to do here with an actual bending of the 

 kathode-rays, or whether the result is due to secondary action, 

 must be further investigated. It is possible that the Avail at 

 m acts as a negative electrode, and so causes the deviations of 

 the rays. This supposition is supported by the fact that, if a 

 glass rod or a narrow metallic plate be brought into the path of 

 the bundle of rays diverging from a plane surface and near to 

 the kathode, the rays diverge from it in a high degree, as if it 

 were itself a negative electrode. The divergence is increased 

 by interpolating air-sparks in the circuit. 



3. Further, to determine whether the negative vibrations 

 which excite the green light could traverse the ordinary posi- 

 tive discharge, the following experiment was made:— 



a (fig. 12) is an electrode in the form of a disk, b is a point. 

 When a is negative and b positive, a bright green spot ap- 

 pears at m, corresponding to the opening of the tube at c ; at 

 the same time the tube at c shines with violet light of the 

 same colour as a tube through which no kathode-rays pass. 



