436 
PHYSICS: L. B. LOEB 
Proc. N. a. S. 
The method used for the investigation of this question was to measure 
the mobihties of the carriers generated as photoelectrons from one plate 
of a condenser using the Rutherford^ alternating current method. Light 
from a quartz mercury arc passed through a quartz window sealed into 
the side of the brass case housing the condenser and was focussed upon 
the lower plate of the condenser by means of a quartz lens. The diameter 
of the plates was 10 cm. and the distance between them 1.65 cm. The 
upper plate of the condenser was connected to a quadrant electrometer 
T 
Y 
r 
V 
-I 
V 
V. 
30 
28 
26 
I- 
C 22 
J 
I 
I 
18 
16 
V in l/o/fs> 
FIG. 1 
Air. Press = 95 mm. I — Saturation; II — N = 148 
of sensibility 3700 mm. per volt. The lower plate led to a commutator 
fed by a large battery of dry cells and capable of giving an alternating 
potential of square wave form of frequency from 15 cycles per second to 
750 cycles per second. Connections were so arranged that the positive, 
or retarding, side of the wave was always about 20% higher than the corre- 
sponding negative, or accelerating, side of the wave. 
The nitrogen gas which came from a tank of commercial nitrogen was 
passed over red hot CuO, red hot Cu, over KOH, and CaCl2, over P2O5 
and finally through a liquid air trap. The commercial hydrogen used 
was purified in the same way omitting naturally the tube of CuO. The 
system including the metal housing for the condenser plates was set up 
so as to eliminate as far as possible all organic vapors such as those coming 
