566 
Rev. P. J. Kirkby on the 
are repeated with little error, and the decrease in R, and 
therefore the increase in X, is strictly proportional to the 
increase in D — facts which prove that very little change 
occurs in the region of high force near the cathode during a 
series of discharges with the same current. This steadiness 
is shown by Table II., which gives the results of a series 
of experiments with gradually diminishing pressure upon 
freshly introduced oxygen during my earlier experiments 
with zinc electrodes (diameter 2-1 cms.). The total dura- 
tion of the discharges used for these observations was about 
Table II. 
p. 
Y. 
25-6 y; + -9. 
•804 
21-4 
21-5 
•75 
198 
201 
•72 
192 
193 
•69 
1835 
18-5 
•66 
1785 
177 
•643 
17-25 
1735 
•617 
16-8 
167 
•58 
158 
lot 
•534 
14-42 
14-55 
3 minutes ; and it may be taken that ultimately 10 per cent, 
of the gas was ozone. The numbers show an extremely 
accurate agreement, and prove that the curve is very straight 
to the left of the discontinuity; for every value of Y but one 
differs from 25"6 / v > + *9 by less than 1 per cent. 
Table II. exhibits great consistency in the observations, 
which were made rapidly, and all but the first and last with 
two observations only. In fact it is experiments like these, 
made with a steady discharge, that establish the validity of 
the method and prove that the positive column can be 
lengthened without otherwise sensibly affecting the discharge. 
We can also infer from the table that the presence of a good 
deal of ozone does not greatly modify the force Y when p is 
less than *8. 
Table III. contains the results of experiments, other than 
those in Table II., made with the zinc electrodes. The per- 
centage errors in the values of Y, most of which w r ere 
determined by several observations, is not more than 4 and in 
