310 
PHYSICS: L. B. LOEB 
Proc. N. A. S. 
points plotted are the actual experimental values of K obtained under the 
conditions of p, Vq, and d given. When the inaccuracies of such meas- 
urements are considered it is seen that the above equation represents the 
behavior of K to a satisfactoiy degree of approximation. 
The success in measuring mobilities of such high values is probably 
due to the fact that especial care was taken to avoid contaminating gases, 
and to the fact that the frequencies employed were very high. The latter 
factor made it possible to measure the mobilities of purely electronic car- 
riers only, for with the short intervals of time used only electrons which 
had made no attachments at all could succeed in crossing the plates. It 
seems likely that the low electronic mobilities observed by the previous 
workers were found for electrons which had been completely free for only 
a portion of their path between the plates because of the low frequencies 
of alternation used. The magnitude of the values obtained in these 
experiments is more nearly in accord with the values of electron mobili- 
ties predicted on the basis of the equations of Townsend 4 and Lenard 6 
(i.e. of 6940 cm. /sec. and 4260 cm. /sec. respectively), than the earlier values. 
The fact that K is not a constant is most interesting. It indicates that 
the term mobility constant has no significance for electrons; since their 
velocity in the field is no longer directly proportional to the field strength 
and inversely proportional to the pressure. The way in which K varies 
with Vo/d and with p indicates that the velocity of drift of the electrons in 
the direction of the field is influenced by the energy gained by the electron 
in the electrical field between impacts. A variation of the energy of the 
electron in the field such as would cause the observed variation of K can 
only occur when the electrons make partially elastic impacts with the gas 
molecules. 
A more detailed account of these experiments will later appear elsewhere. 
The experiments are being extended to hydrogen and if possible to other 
gases. 
* National Research Fellow of the National Research Council 
1 Loeb, L. B., these Proceedings, 6, 1920 (335). 
2 Loeb, L. B., Physic. Rev. (N. S.)» 17, 1921 (94). 
3 Haines, W. B., Phil. Mag., 30, 1915 (503). 
4 Townsend, J. S., Electricity in Gases, Oxford, 1914 (174 ff ) ; also Phil. Mag., 40, 1920. 
« Lenard, P., Ann. Physik, 40, 1913 (409). 
