394 
e. And this forms in our opinion the connecting link to the view 
recently set forth by J. J. Tuomson, according to which he assumes 
that electro-luminescence radiation chiefly takes place with recom- 
bination of free electrons with ions (Phil. Mag. 37, 419, 1919) *). 
It seems to me that after the above remarks some difficulties 
would have to be removed if this view is to be maintained. But it zs 
clear that particularly when radiation is excited by a strong external 
electric source of energy, ions must appear, and to these rests them- 
selves the strong emission of light is, in fact, chiefly owing. 
That on combination of the ion with an electron a great distur- 
bance in the molecule takes place, which likewise gives rise to 
light-emission of the different “erregte” states, is clear. That such 
an emission of light takes place in case of the return we have dis- 
cussed, has experimentally been made very probable by P. LeENARD 
for the region of phosphorescence. 
8. Summary. 
As a summary we may give the following conclusions from some 
results of the author’s Thesis for the Doctorate and the preceding 
calculations : 
1. The observed pressure effects are chiefly owing to the difference 
in the number of molecules that arises on the discharge of the 
positive and negative ions at anode and cathode. In direct sense 
the electric wind plays only a very subordinate part. The extent 
of the pressure differences varies with number, mass, charge, mobility 
of the positive and the negative ions. Hence the dependence on the 
electric variables, the gas pressure, the nature of the gas. 
It appears possible to come to a physical interpretation of the 
factors, leading to the pressure effect (Ap), the consequences of which 
are also in harmony with the dependence of Ap on different. variables. 
2. There occur positive and negative ions charged with mass in 
the luminous positive column, and also electrons in a considerable 
degree. The current-conveyance is chiefly brought about by the latter. 
3. The conclusions under 1 and 2 form in the region of electro- 
luminescence experimentally and logically a support for the theories 
and views of Cuirp, Frank, and Hertz, and to a certain extent to 
those of THomson as indicated above. 
4. The outer electrons of the atom determine the catalytic proper- 
ties. The right of existence of the assumption of dislocated states in 
the theory of catalysis is optically confirmed. 
Dordrecht, March 1920. 
1) Cf. also Engineering 107, 410 (1919). 
