194 Mr. S. Ratner on Polarization 



on being released from the electrodes during discharge. 

 The nature of the electrodes themselves, according to all 

 experimental data, has but little influence upon the sparking 

 potential and upon the amount of the current which flows 

 through the tube. 



In the course, however, of some experiments with an 

 X-ray bulb through which a continuous discharge was 

 maintained for a long time, the writer has observed a 

 gradual hardening of the bulb in spite of the maintenance 

 of a comparatively high pressure which could be controlled 

 throughout the experiments by a Gaede pump and measured 

 by a McLeod gauge connected to the bulb, Further 

 experiments carried out in this direction have revealed a 

 remarkable effect which takes place in an X-ray bulb or, 

 more generally, in any vacuum tube after a sufficiently long 

 and constant run. This is, that after a discharge has been 

 kept running long enough, a time arrives where the resis- 

 tance of the bulb begins to increase gradually, and finally 

 becomes sufficiently high to stop the discharge altogether, 

 although the pressure still remains constant and compara- 

 tively high. This phenomenon is somewhat analogous to 

 the polarization of an electrolytic cell, and for the sake of: 

 brevity shall, in what follows, be referred to as a polarization 

 effect. 



The present paper contains a description of the procedure 

 by which an X-ray bulb may be polarized, as well as the 

 results of some experiments carried out with such a bulb. 



Apparatus and Procedure. 



2. The bulb used was constructed for other purposes, being 

 of the type described by Rausch von Traubenberg *. 



The aluminium cathode (fig. 1) is introduced into 

 the bulb by means of the ground joint G. The anode 

 consists of a slightly inclined copper plate A, 5 cm. in' 

 diam., fitting into the bottom of a brass cylinder B, 4 cm. 

 long, into which the neck of the bulb is sealed with white wax. 

 This cylinder has a narrow slit S, about 4 cm. long, cut 

 round the cylinder and covered with thin aluminium foil, 

 through which the beam of X-rays could pass with very little 

 absorption. Plates of aluminium of different thicknesses 

 could be put between the aluminium window and a fluo- 

 rescent screen placed in a dark camera (not shown in the 

 figure) — an arrangement by means of which the penetrating- 

 power of the X-ray beam could be roughly estimated. The 



* Rausch von Traubenberg, Phys. Zeits, xviii. p. 241 (1912). 



