Conducting Gases on the Direction of the Electric Field. 227 

 Substituting in the equation 



-kr 32-7T d z i x 



5> ' 



and expressing V in E.S. units, we find the value of" K t 

 1450 cms. per sec., i. e. Kj = 4*8 cms. per sec. for 1 volt 

 per cm. 



The value found recently by Zeleny was 1*36 for dry air. 



The value obtained from the equation is thus much too high, 

 for the reasons explained above. 



Application of Results to Flames. 



In the course of this paper, numerical results have been 

 given only for the differences between currents due to reversal 

 of electric field, for ions produced by Rontgen-rays and radio- 

 active substances. The general explanation, however, applies 

 equally well to production of ions by all known agencies. 

 Whenever there is strong unsymmetrical ionization and dif- 

 ference between the velocity of the ions, the currents in the 

 two directions will always be unequal. 



Child's results show clearly that in the case of ions drawn 

 from the flame into a region outside, the currents are unequal, 

 on account of a difference in the velocity of the ions. 



It seems probable that the so-called " unipolar conduc- 

 tivity " of flames can in many cases be explained purely on 

 the assumption of unequal velocities of the ions. In flame- 

 conduction, where the electrodes are unequal, we have all the 

 conditions necessary to cause unequal currents ; for the 

 ionization produced both in the flame itself and at the surface 

 of the electrodes is very intense, and the negative ion also 

 moves much faster than the positive. The subject is, however, 

 a very complicated one, and it is unlikely that the same expla- 

 nation will apply for all cases. 



Wilson, Marx, and others have shown that the ionization 

 in a flame depends largely on the temperature of the electrodes, 

 and is confined mainly to the glowing electrodes. There is 

 always, however, a certain amount of volume ionization 

 throughout the gas. In the case of unequal electrodes at a 

 white heat, the inequality of the currents is probably due 

 almost entirely to the greater velocity of the negative ion ; 

 for in this case the glowing electrodes produce a numerous 

 supply of positive and negative ions. With electrodes at a 

 lower temperature, however, the matter is complicated by 

 the fact that the electrodes discharge positive and negative 

 electricity unequally. For example. Elster and Geitel have 



Q2 



