388 
forth inter alia in the next paragraph, formula 7 is therefore to be 
preferred. 
e. It should now also be pointed out that it follows from equation 
7 that Ap is proportional to the strength of the current, which as 
was already stated by us (ef. Thesis for the doctorate) has also been 
established experimentally for nitrogen. 
It may, however, happen that with higher current densities there 
appear other bearers, as e.g. is very probable for argon. It is to be 
regretted that sufficient quantitative data are wanting about the 
dependence of the pressure effect on the current density in this gas. 
In general it may be said a priori that the pressure effect cannot 
be a simple function of the gas pressure, because, as is known, 
other bearers will occur for important variations of the pressure. 
One and the same supposition will not always serve our purpose. 
With very low pressures and with high potential differences electrons, 
instead of charged atoms or molecules, can be discharged at the 
electrodes to such an important degree, that the pressure effect even 
reverses its sign (STARK, WeHNELT and Frank loc. cit’). In this sense 
we have distinguished two categories on page 383. 
As was already stated at the end of § 5 under a the preceding 
calculations have, indeed, only been given to show that the difference 
in properties of the positive and negative ions can actually give rise 
to important pressure effects, which are of an entirely different order 
of magnitude than those which should be considered as ensuing 
directly from the electric wind. It is, therefore, necessary to point 
out here, apart from the criticism given in the following paragrapb, 
that in general the phenomena met with, are very complicated, 
especially for high gas pressures. We should, therefore, not be very 
optimistic with regard to a satisfactory, mathematical treatment of 
this subject. 
6. Criticism; Modification of. the Physical View. 
Both equation 7 and equation 8 have been obtained by combi- 
nation of equation 5 with equations of diffusion. We remind that 
in § 5 under 6 it was given by way of supposition: “Let us think 
the current cut out for a moment with given difference of pressure, 
and all the ions re-combined to neutral molecules. Then the gas 
must flow back through the capillary.” After this the diffusion laws 
are applied. 
In reality, however, the measurements are made, while the current 
has not been cut out. 
Then exceedingly important processes take place in the capillary 
