340 
PEOFESSOE W. Gr. ADAMS AND ME. E. E. DAT ON THE 
deflection, due to the passage of the battery-current alone, was 50 to the right of zero. 
The lime-light was then focused on the marked end, i. e. the end where the current 
was leaving the selenium, and the resulting deflection due to the light and the current 
combined was 70 to the right. 
In another experiment, with the electrodes in the same positions, the deflection when 
the selenium was not exposed, and when the battery-current alone was passing, was 35 
to the right, and on focusing the light on the end where the current was leaving the 
selenium, the deflection was 52 to the right. 
In all these cases, the action due to the light was almost instantaneous, and the 
deflection came back at once to its original value when the light was screened off. 
In another experiment, when the positive current entered the selenium at the 
unmarked end, the deflection before exposure was 40 to the left of zero; and when the 
lime-light was focused on the same end, i. e. the end where the current was entering 
the selenium, the deflection was 20 to the left. 
The battery-current was then cut off, and the same end being exposed to the action 
of the lime-light, a deflection of 20 to the right indicated a current of that intensity 
from the selenium to the platinum at the illuminated end, just as if there had been no 
original current. 
The electrodes of No. 25 were then again reversed in the mercury-cups, so that the 
positive current from the battery should enter at the marked end. The deflection 
before exposure was 40 to the left. The light was then focused on the unmarked end, 
and the deflection was at once increased to 65 to the left, and back again to 42 on 
screening off the light. Repeating this experiment we had, before exposure, a deflection 
of 43 to the left, and on exposure a deflection of 70 to the left of zero. 
The positive current was then sent in at the unmarked end, and produced a deflection 
of 30 to the right. The light being focused on the unmarked end, the deflection was 
reduced to 8 to the right of zero. 
Tube No. 24 was next examined in the same way, with the following results : — 
Deflections. 
(1) + Current entering at the marked end 50 to the left. 
ditto ditto light on the marked end 45 „ „ 
(2) + Current entering at the unmarked end 40 to the right. 
ditto ditto light on marked end 47 „ „ 
(3) + Current entering at the marked end 50 to the right. 
ditto ditto light on unmarked end 60 „ „ 
(4) + Current in at the unmarked end 52 to the left. 
ditto ditto light on unmarked end 44 „ „ 
These experiments were repeated several times with similar results, and point to the 
same conclusions as those made with No. 25. 
Tube No. 23 was then examined in the same way, with the following results : — 
