380 
3. Mass Transportation by means of the Electric Current. 
The discharge of the ions taking place at the electrodes, 1owever, 
gives rise to a state which may be considered as an accumulation 
of what was discussed before. 
To the existing difference in properties of the oppositely charged 
ions corresponds to a certain extent the difference between the gas 
molecules formed from them by the discharge at the electrodes. 
Though the direct influence of the difference of the ions on the gas 
pressure is slight, the influence on the gas pressure assumes quite 
different proportions when it is kept in view that constantly the 
electrically charged particles withdraw from the ion-conditions. 
Resting on the same primary basis as the electrical wind, this 
accumulation leads to the effect that manifests itself much more 
strongly: mass-transportation by means of the electric current. 
In general on discharge of the ions taking place at the electrodes, 
another number of gas molecules will be liberated at the cathode 
than at the anode. 
[n consequence of this a constantly increasing difference of pressure 
would be found in the two parts of the tube, if not another counter- 
acting effect made itself felt. It is, indeed, clear that, when a difference 
in pressure occurs through the application of the electric field, the 
gas molecules will oppose this, and try to annihilate the difference 
in pressure by diffusion in the opposite sense. The resulting difference 
of pressure then corresponds to a stationary state, in which an equal 
number of molecules are brought back to the path of the current 
through diffusion, as new ones — in ion-form — are conducted to 
the electrodes by means of the electric current. 
Already J. Srark (loc. cit.) has carried out a few preliminary 
calculations on this line of thought. As at the time, however, the 
aerodynamic laws for greatly diluted gases had not yet been developed, 
his calculations are based on unsubstantiated grounds. Thus he arbi- 
trarily assumes that after ten seconds the diffusion would make 
equilibrium with the mass transportation brought about by the current. 
Already A. WennNerLT and J. FRANK’) tried to find a firmer foundation 
for their calculation. In their experiments, just as in those by STARK, 
the circumstances under which the experiments were carried out, 
were chosen so that the carriers of the negative electricity were 
present only in the form of electrons. In what follows we shall 
extend the cases to be considered over a somewhat wider region. 
Let us, however, first examine on what conditions the diffusion under 
1) Verh. d. D. phys. Ges. 12, 444 (1910). 
