467 



ƒ/ for il definite gas arc concerned, this influence is also theoretically 



comprehensible. It already follows directlj from the equation (4) of 



our former coramnnication (I loc. cit. p. 384) which is based on 



the equation of motion of the electrically charged particles in the 



electric field, and from which appears the proportionality with the 



potential gradient V, piovided the nature of the bearers undergo 



no change witii V. 



Already for this reason we may express this also in the equation 



of I he mass-transportation by the electric current: 



1 ^ 760 



mass-transportation =r — Q . A . . 2,32 10-* ^) 



a p 



1 



(equation {dl communication I), by replacing - there by a factor 



bg, in which b is a. constant for a definite gas. Hence — ^= h or 



a.g 

 ag z= constant. 



Let us also try to derive this directly from the nature of the 



electric conduction, and at the same time ascertain from it whether 



01' no b has the same value for different gases. We then remind 



the reader that equation (9) of communication I teaches us that the 



1 

 pressure effect must be proportional to the part - of the conduction, 



which takes place through ions charged with mass. This part is in 

 direct ratio to the concentration of the ponderable ions. The pi-oblem 

 may, therefore, be reduced to the question whether increase of g 

 can cause increase of the concentration of the ions. In case of 

 proportionality the equation ag =■■ constant may then be applied. *) 

 This relation will actually have validity for electropositive and 

 noble gases, when J. Franck and G. Hkrtz's ') elementary theory 

 is adopted, according to which, as is knowji, perfectly elastic collis- 

 ions between electron and atoms are assumed to take place, till — 

 under infiuence of the electric field — the electron has passed over 

 such a distance, and in this has obtained so much energy that its 

 energy exceeds the value connected with the ionisation tension. Tlie 

 greater g, the shorter the time in which this value is obtained ; the 



^) With regard to the factor Q in the numerator, see note 1, p. 465. 



*) We neglect tlie electrons liberated at the formation of the positive ions, sup- 

 posing that within stationary conditions as many of these electrons are disappearing 

 by recombination and formation of negative ions charged witli mass. Additionally 

 it may be remarked, that in the field of this investigation the number of ions 

 compared with the number of free electrons is very small. 



We intend to deal within short time more fully with this part of the subject. 



») J. Franck and G. Hertz. Verli. d. D. phys. Ges. 18, 213 ('16). 



