90 'Prof. E.Wiedemann on the 



The fact that these rotations have not yet been observed 

 in air, although with the kathode-rays they attain so high a 

 value, may be to some extent accounted for as follows. 



The rotation of the plane of polarization « is expressed, 

 other conditions being unchanged, by the formula 



A ^B . 



where A, B, &c. are constants, and X denotes the wave-length. 

 ot attains a greater value the smaller \ is; and it increases 

 much more rapidly than X does. 



But this cannDt be the whole of the explanation of the 

 difference in behaviour between the kathode-rays and ordi- 

 nary rays of light. If the rotation of the vibrations of light 

 were equally great, whether it takes place in the plane passing 

 through them and the ray of light, or in a plane at right angles 

 to this, then this rotation could certainly be distinctly observed 

 by placing a cylinder of Faraday's glass equatorially between 

 the poles of a powerful electromagnet, and sending through 

 it a ray of light coming from a slit through a collimator, and 

 observed with a telescope provided with cross-wires. Expe- 

 riments for this purpose have, however, given only negative 

 results. 



7. On the Positive Discharge and the Formation of Stratifica- 

 tions. — I propose to describe in few words a theory I have 

 formed as to the cause of the stratifications, which affords an 

 explanation of a series of phenomena, and with the further 

 development of which I am now occupied. 



There is formed round the negative electrode, as we have 

 seen, a space in which the gas is in a condition altogether 

 different from that in the rest of the tube. There is a dielec- 

 tric polarization at the positive electrode, which undergoes 

 a change when the discharge takes place: this (and not a 

 sound-wave) is transmitted, and is followed by a current of 

 free electricity*. When this advancing dielectric polarization 

 reaches the neighbourhood of the kathode, it, like any other 

 tension, is reflected, and the return-wave produces interfe- 

 rence; the following electricity finds therefore places of maxi- 

 mum and minimum motion; in the first it will behave in a 

 different way than in the latter: in the first, therefore, the 

 gas is seen to be luminous, in the second not. 



Since the anode itself must always be a point of maximum 

 motion, it corresponds to a layer, a bright point, even when 

 the distance of the anode from the reflecting parts of the 



* Compare the conclusions in Wied. Ann. x. p. 245, and the reclama- 

 tion of W. Siemens, Wied. Ann. xxix. p. 117 (1880). 



