Vol. 7, 1921 
PHYSICS: L. B. LOEB 
309 
pressure by means of the equation, K=(pU)/760, where p is the pressure 
in mm. of mercury. 
The mobilities found in this manner were astonishingly high. At 600 
mm. mobilities of the order of magnitude of 15,000 cm. / sec. were obtained, 
while the highest previous mobility determined 3 in N 2 was 500 cm. /sec. 
Furthermore the value of K obtained was not a constant as one would 
expect. K was found to be a function of the field strength and pressure. 
For a given pressure the value of K plotted as a function of Vo/d the field 
strength was found to lie on a hyperbola of the form, K= ^ j^yjj 
For different pressures a family of such hyperbolae were obtained which 
were expressed by the equation, 
K = 571,000 
21+760 V Q /(pd) ' 
This is shown in figure 2. The full curves are drawn from the above equa- 
tion at values of p and d at which the measurements were made. The 
u~ Volts 
FIG. 2 
