Positive Column in Oxygen* 
567 
most cases less than 2 or 3. Each compartment of Table III. 
applies to experiments upon the same specimen of oxygen. 
Table III. 
p. 
Y. 
p. 
Y. 
p. 
Y. 
102 
7-5 
626 
15 
j 1-02 
75 
•495 
13-1 
4-2 
6-6 
•79 
20-4 
3-2 
242 
5-25 
4-04 
1 
2-02 
4-6 
•785 
20-4 
.r-O 
19-2 
17-6 
4-0 
8-2 j 
2-9 
5-9 
•7 
2-36 
4-4 
•686 
17-8 


1-49 
615 
•49 
12o 
•88 
11-7 
The numbers in Table III. are with two exceptions suffi- 
ciently concordant, although the oxygen had in many cases 
been subjected to much discharge. They determine a curve 
which is nearly identical with that of fig. 2 for pressures 
below 2 mnis., but falls much below it when p exceeds 2 mms. 
Thus, when p exceeds 4, Y is less than two-thirds of its cor- 
responding value in fig. 2. This large difference cannot be 
attributed to the small difference in the discharge-tubes ; 
especially since the latter difference should make — if we can 
be guided by the behaviour of nitrogen * — the values of Y in 
Table III. greater than those in Table I. 
Hence the conclusion is forced that the divergence is due 
to the use of different electrodes. This conclusion is con- 
firmed by my experiments with silver electrodes, which gave 
a general agreement with the foregoing results for pressures 
less than 2*5 mms., and at first gave the usual pressure of 
discontinuity. But partly perhaps owing to the cathode's 
not fitting the tube, and chiefly, I believe, to the oxidation 
of the electrodes, these experiments left few numbers to rely 
on or worth recording. It may be remarked, however, that 
when the electrodes became badly attacked, the pressure of 
discontinuity was thrown back to the point '62 mms., and 
the values of Y on both sides of it were then reduced to 8 
and 18. 
* Herz found that the electric force in nitrogen was 997 and 89*3 for 
tubes 10 and 20 mms. in diameter respectively. — J. J. Thomson, I. c. 
ch. xv. 
