PHYSICS: K.-L. YEN 
small in comparison with those of the uncharged molecules in the same gases. 
They also explain equally well a certain number of other phenomena, but 
experiments designed to test directly the validity of one or the other of these 
hypotheses led to contradictory results. 
The measurement of the mobilities of ions under various pressures and 
different electric field-strengths has always been generally conceded as the 
mode of attack in the solution of the problem. For if the older, the cluster, 
hypothesis is true the cluster would break up when the ion acquired a suffi- 
ciently high kinetic energy and the mobility would increase abnormally. But 
if the small-ion theory is true there would be no such dissociation and the 
mobility would remain normal. Quite a number of such measurements have 
been made, and they gave contradictory results. For instance, Latty, 1 
Kovarick, 2 Todd, 3 Townsend, 4 Franck, 5 Moore, 6 Haines, 7 and Ratner 8 found 
the mobility to increase abnormally, whereas Chattock, 9 Wellisch, 10 - 11 and 
Loeb 12 found it normal over a wide range of potentials applied. In view 
of these results further experiments seemed desirable and hence the work 
herein described was undertaken. 
The method here employed was the Rutherford 13 -Franck 14 method as em- 
ployed by Loeb. 12 The apparatus was fully described in Loeb's articles. 
Results: a. Air. — An attempt first to repeat Loeb's work with air gave the 
following results: 
TABLE 1 
Table of Results Obtained for Ionic Mobilities in Air, February-March, 1917 
u+ 
u- 
X+ . 
X- 
P 
K+ 
K- 
R 
1. 60 cycles, 119 volts 
1.12 
1.75 
168 
134 
746 
1.10 
1.72 
1.56 
1.12 
1.75 
168 
134 
746 
1.10 
1.72 
1.56 
1.12 
1.75 
168 
134 
752 
1.10 
1.73 
1.56 
1.25 
1.73 
168 
134 
742 
1.22 
1.70 
1.38 
Mean 
1.14 
1.72 
1.51 . 
2. 
14,758 cycles, 5000 volts 
1.64 
1.98 
14,160 
12,870 
752 
1.62 
1.92 
1.21 
1.57 
1.84 
14,160 
12,870 
750 
1.56 
1.82 
1.17 
1.64 
1.98 
14,160 
12,870 
749 
1.61 
1.95 
1.21 
1.57 
1.84 
14,160 
12,870 
746 
1.55 
1.81 
1.17 
1.82 
2.10 
13,810 
12,650 
692 
1.66 
1.92 
1.17 
2.26 
2.61 
12,300 
11,550 
558 
1.66 
1.91 
1.16 
Mean 
1.61 
1.90 
1.18 
Mean of both sets 
1.37 
1.81 
1.34 
U+ = 
Mobility of positive ions. U — = 
Mobility 
of negative ions. 
X = Field 
strength in volt/cm. P = Pressure in mm. R = K — /K. K = Mobility at 760 mm. pres. 
X - IP Max. - 20.70, Min. = 0.18. X + /P Max. = 22.04, Min. = 0.22. 
