JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VII DECEMBER 4, 1917 No. 20 



PHYSICS. — Anode resistance films. John T. Tate and Paul 

 D. Foote, Bureau of Standards. 



In a previous paper 1 it was concluded that a polarization 

 film of high resistance forms at the surface of a probe placed in 

 the anode glow of a Wehnelt discharge tube. In the measure- 

 ments referred to, the probe wire acted as an anode. It is of 

 interest to compare the film resistance when the probe acts as 

 an anode with that obtained when the probe acts as a cathode. 



The experimental arrangement was that illustrated in the 

 paper already referred to. For the probe as anode the same 

 electrical connections were employed. For the probe as cathode 

 the potentiometer and voltmeter readings were taken between 

 the probe and the Wehnelt cathode. Resistances were com- 

 puted in the manner previously described. The results of one 

 series of measurements are represented by figure 1. For the 

 same current flowing through the probe the film resistance is 4 

 to 6 times greater when the probe acts as a cathode than when it 

 acts as an anode. The ratio of resistances R cathode : R anode 

 increases with increasing current through the probe. It has 

 been generally assumed that the anode resistance film is negligi- 

 ble in magnitude as compared with the cathode resistance film. 

 The small values of the ratio RdR* observed are therefore of 

 interest. It is also of interest to note that the ratio of the resist- 

 ances of the cathode and anode films is of the same order of 



1 This Journal 7 : 482. 1917. 



593 



