308 
PHYSICS: L. B. LOEB 
Proc. N. A. S. 
FIG. 1 
irnd 2 
u= iw: 
in order to evaluate the mobility U. In this equation n is the frequency 
of the alternations, d is the distance between the plates in cm. and Vq 
is the voltage in volts as read from the static voltmeter. In the oscil- 
lating circuits the potential was varied by varying the resistance r of the 
plate circuit. Since varying r altered the frequency n slightly the 
frequency of the oscillations was determined by means of a wave meter 
for several values of the voltage used in each determination. The 
experiments reported here covered a range of pressures from 600 mm. to 
75 mm. The frequencies used varied from 7000 cycles per second to 
150,000 cycles. The voltages used were varied from 10 volts to 300 volts 
and the plate distances lay between 2. 0 cm. and 1.5 cm. The values of U 
thus obtained were reduced to give the mobility constant K at atmospheric 
