Negative Ions by Glowing Metallic Oxides. 85 



the same value as that for platinum. From this Mr. 

 liichardson concludes that the corpuscles proceed not from 

 the glowing oxide, but from the platinum, and that the action 

 of the oxides is confined to a reduction of the amount of 

 energy required to liberate the corpuscles. Experiments to 

 settle this point are in progress at this Institute. 



III. Glowing Metallic Oxides as Cathodes in Discharge 

 Tubes, 



According to our modern views, the cathode dark space of 

 a glow discharge represents a region poor in negative ions*. 

 If this impoverishment is prevented by introducing into the 

 dark space corpuscles produced by any convenient method, 

 their presence results — as has been shown experimentally by 

 Herr G. C. Schmidt — in a lowering of the potential drop at 

 the cathode. 



Now glowing metallic oxides emit, as we have seen, 

 numerous negative ions. Hence, when used as cathodes 

 they should produce a lowering of the cathode drop which 

 increases with increasing temperature. 



Experiments on this point confirmed the truth of this 

 conclusion. 



In what follows are given the results of quantitative ex- 

 periments made to determine the connexion between the 

 cathode drop on the one hand, and the current, pressure, and 

 temperature of the metallic oxide cathode on the other. 



The spherical discharge-tube used in the experiments had 

 for cathode a platinum wire coated with the oxide under 

 investigation, the wire being heated by an alternating current. 

 The temperature was measured by means of a very thin 

 platinum-platinum-rhodium thermocouple. An exploring 

 electrode near the cathode enabled the cathode drop to be 

 measured. A wire of aluminium served as anode. 



Connexion between Cathode Drop and Current. — In the first 

 place, I investigated the dependence of the cathode drop on 

 the current at various temperatures of the cathode. The 

 results for the oxides of barium, calcium, and strontium are 

 almost identical, qualitatively as well as quantitatively, so 

 that I here give, in Table III., only the values obtained with 

 CaO. 



* J. J. Thomson, Phil. Mag. xlvii. p. 253 (1899). J. Stark, Ann. d- 

 Physik, ii. p. 62 (1900). G. C. Schmidt, Ann. d. Physik, xii. p. 622 (1903). 

 A. Wehnelt, Ann. d. Physik, x. p. 569 (1903). 



