Intelligence and Miscellaneous Articles. 548 



ON THE GLOW-DISCHARGE. BY E. WARBURG. 



The results of the present investigation are thus summarized by 

 the author : — 



1. The electrostatic attraction which a plane cathode surface 

 experiences in the glow-discharge can be measured by the balance, 

 and from it the electrical force and the surface-density on the 

 cathode surface can be determined. That attraction is proportional 

 to the density of the current, r and for bright platinum and aluminium 

 electrodes amounts, in milligrammes per ampere, in 



Dry nitrogen from 0'5 to 2 mm. pressure, 1300-2400. 



Slightly moist nitrogen . . „ „ „ 500-800. 



Hydrogen from 1-3 mm. pressure, 200-350. 



2. In the negative glow-light there is, as A. Schuster has pointed 

 out*, an excess of free positive electricity. The amount of this 

 positive charge is opposite and equal to the negative charge of the 

 cathode. Like this charge it is proportional to the square root of 

 the density of the current, and has been found to amount to about 



10 ~ 10 for 1 milliampere per square centimetre with bright 



platinum and aluminium cathodes in nitrogen and hydrogen. 



3. The surface of an anode is much more feebly attracted, and is 

 therefore much more feebly charged than the surface of a cathode. 



If, then, two infinitely large parallel electrode surfaces are oppo- 

 site each other, they are equally strongly charged only so long 

 as the electricity is in equilibrium. If, however, the glow-discharge 

 passes between the surfaces, the charge of the anode is feebler than 

 the charge of the cathode by the excess of free positive electricity 

 which is present in the gas through which the current passes. 



4. At the normal density at which the negative glow-light can 

 spread freely over the cathode, the electrical force at the cathode 

 decreases with decrease of pressure, and is less for hydrogen than 

 for nitrogen, in accordance with the laws of the striking-distance. 

 At normal density, therefore, the excess of free positive electricity 

 in the gas, mentioned under 3, decreases with decrease of pressure. 



5. The material electrical charge of the gas which takes place in 

 the glow-discharge brings with it an increase of the hydrostatic 

 pressure, and therefore under ordinary circumstances produces 

 eddy currents, which flow between limited electrodes from the 

 anode to the cathode, and may account for the so frequently 

 observed transfer of matter in the direction of the positive current. 

 — "Wiedemann's Annalen, No. 1, 1892. 



* Proc. Eoy. Soc. vol. xlvii. p. 541 (1890). 



