332 
PBOEESSOB W. G. ADAMS AND ME. K. E. DAY ON THE 
In the next set of experiments tube No. 11 was used. The resistance of this piece of 
selenium is small, being only '0143 of a megohm. The current from 2 Leclanche cells 
was sent through it each time for a period of 5 minutes, and then the resulting 
polarization-current was measured : — 
Interval between tbe experiments. Polarization-current. 
0 — 25 
8 minutes — 49 
8 „ — 76 
11 „ -112 
This piece was then examined with a stronger battery-power, namely, that of 
20 cells. The time during which the battery-current was kept on is indicated in the 
second column : — 
Duration. Polarization-current. 
5 minutes — 550 
3 „ -560 
5 „ -450 
10 „ -480 
In these experiments the 10th shunt had to be used with the galvanometer, so as to 
keep the spot of light on the scale. 
Exposure to Light alters the Strength of the Polarization-current. 
All the results given by the above experiments were obtained while the selenium was 
kept in the dark. 
In a few experiments of a similar character made with Nos. 11 and 2 an attempt was 
made to discover whether, on exposing the selenium to light during the passage of the 
; polarization-current , any change in the intensity of that current would be produced. 
In the case of No. 11, there appeared to be a slight increase in the intensity of the 
polarization-current during exposure, and a decrease in the intensity on shutting off 
the light. 
An experiment with tube No. 2 showed this action rather more conclusively. A 
current represented by a deflection of 146 X 10 3 having been sent for 15 minutes through 
No. 2, gave a steady polarization-current of 9 divisions of the scale. On exposing the 
selenium to the light of the galvanometer-lamp, the deflection was at once increased to 
14, and on screening off the light the deflection came back at once to 11. 
The current from the 20-cell Leclanche’s battery having been sent through No. 15 
in the positive direction for about half a minute, gave a polarization-current indicated 
by a steady deflection of 25 scale-divisions to the left of zero. On exposing the selenium 
to the light of a candle at a distance of 6 inches, the spot of light came gradually down 
Time when current 
was put on. 
1.32 p.m. . . 
2.5 „ . . 
2.38 „ . . 
2.49 „ . . 
