/ 
348 PHYSICS: L. B. LOEB 
two columns the critical distances in centimeters are given. The 
next two give the mobilities. The next column gives the pressure in 
millimeters of mercury. The next columns give the values of the 
mobiHties reduced to 760 mm. pressure. The last two columns give 
the field strengths for the maximum values of the fields in volts per 
centimeter. 
The measurements were carried up to fields of 12,450 volts per 
centimeter in air at atmospheric pressure, and to somewhat lower field 
strengths at pressures as low as 300 mm. of mercury. The results could 
not be extended to higher field strengths nor lower pressures, because 
TABLE I 
Ionic Mobilities Obtained with Chaffee Arc 
N 
d- 
"+ 
u— 
p 
^+ 
U- 
X- 
mm. 
60 
0.99 
1.38 
1.10 
2.12 
760 
1.10 
2.12 
121 
87 
60 
1.00 
1.26 
1.13 
1.78 
756 
1.12 
1.76 
120 
96 
*60 
1.00 
1.28 
1.13 
1.85 
748 
1.12 
1.84 
118 
93 
60 
1.33 
1.56 
1.95 
2.70 
578 
1.48 
2.05 
91 
77 
7670 
0.50 
0.97 
750 
0.98 
12,450 
7670 
0.55 
0.64 
1.17 
1.59 
746 
1.19 
1.62 
11.460 
9,750 
7670 
0.54 
0.61 
1.07 
1.37 
747 
1.09 
1.40 
11,550 
10,200 
7670 
0.50 
0.65 
1.25 
1.80 
735 
1.28 
1.86 
12,450 
9,600 
7670 
0.66 
0.84 
1.70 
2.74 
534 
1.27 
1.95 
9,580 
7,430 
*7670 
0.78 
1.02 
2.36 
4.04 
436 
1.36 
2.32 
8,000 
6,000 
*7670 
0.85 
1.01 
2.72 
3.88 
430 
1.54 
2.18 
7,346 
6,160 
7670 
0.82 
1.10 
2.58 
4.29 
416 
1.41 
2.29 
7,610 
5,670 
7670 
0.85 
0.90 
2.67 
3.07 
384 
1.35 
1.53 
7,340 
6,910 
7670 
0.80 
0.86 
2.51 
2.90 
382 
1.26 
1.46 
7,800 
7,260 
17670 
1.11 
1.22 
4.78 
5.80 
304 
1.96 
2.32 
5,610 
5,160 
Mean Mobilities at 760 mm. 1.33 1.89 
* These readings were taken with very dry air. 
t The value of the + mobihty only estimated here, not determined. 
of the fact that irregularities in the operation of the arc caused serious 
sparking beyond these limits. It can be clearly seen that for a range 
of field strengths extending from 90 volts per centimeter to 12,450 
per centimeter in air at atmospheric pressure, there is neither for the 
positive nor the negative ion any marked increase in the absolute value of 
the mobility. It is also to be noticed that the mobility of the negative ion 
shows no abnormal increase relative to that of the positive ion. In other 
words, in fields of nearly half the value of the sparking field strength 
in air (30,000 volts per centimeter at 760 mm. pressure), and in fields 
where occasional sparking did actually occur (due to irregularities of 
