44(3 
DE. W. MANSEEGH VAELEY OX THE PHOTO-ELECTEIC 
before, of zinc, but tlie experiments were carried out in air. The intensity of the 
lig’bt remained perfectly constant throughout the series. These experhnents were 
caii’ied out in the smaller leak apparatus (the larger being used as the standard) to 
a.void loss of time in pumping betM^een successive sets of observations. The current- 
P.D. curves derived from these results are plotted in fig. 5. 
Table II. 
Potentiiil to which 
zinc is charged 
Current from zinc surface in air in electrometer scale divi.sions in 10 seconds, the 
pressure being— 
in cells. 
(1 cell = 24 A^olts.) 
0-370 
0-206 
0-100 
0-046 
0-019 
0-0038 
0-0014 
millim. 
millim. 
millim. 
millim. 
millim. 
millim. 
millim. 
1 
4 
92 
85 
76 
75 
73 
71 
1 
66 
20 
194 
159 
122 
104 
96 
75 
70 
40 
375 
254 
— 
— 
_ 
_ 
_ 
60 
630 
371 
193 
— 
_ 
_ 
_ 
80 
— 
501 
— 
_ 
_ 
—— 
___ 
100 
- ' 
237 
119 
_ 
_ 
_ 
140 
— 
— 
270 
— 
_ 
_ 
180 
— 
— 
309 
122 
102 
75 
68 1 
A further set of observations was made on the relation between the currents and 
pressin-e, using a platinum electrode Instead of zinc. The larger leak apparatus was 
used, and the ])latinum electrode situated 2 millims. behind the gauze. 1 volt P.D. 
on the electrometer gave a deflection of (35’G scale divisions. The series of observa¬ 
tions was taken in tlie order given in Table III., and it was found that betAveen the 
first and last experiments the light increased nearly 10 per cent, in intensity. This 
increase was gradual, and has been disregarded. 
Table Ill. 
Potential to 
which platinum is 
charged in cells. 
(1 cell = 2-1 volts.) 
Current from platinum surface in air in electrometer scale divisions 
in 15 seconds, the j^ressure being— 
25 millims. 
7 millims. 
2 millims. 
0-24 millim. 
0-061 millim. 
0 ■ 026 millim. 
4 
_ 
_ 
26 
42 
36 
35 
20 
29 
40 
65 
65 
41 
36 
40 
— 
-- 
117 
97 
_ 
60 
42 
62 
200 
125 
_ 
80 
— 
105 
357 
_ 
100 
50 
198 
-- 
162 
44 
120 
— 
406 
_ 
- 
140 
67 
-- 
___ 
209 
_ 
160 
— 
— 
— 
330 
. 
180 
103 
— 
46 
35 
1 
