146 MR JAMES DEWAR AND DR M‘KENDRICK ON THE 
we found that the changes produced by the action of light occurred suddenly, 
and lasted only for a brief period of time, so that there could be no possibility 
of mistaking them for changes in polarity. We have also eliminated as far as 
possible any error from variations in polarity by multiplying experiments and 
by performing them under as favourable conditions as could be devised. Fre- 
quently, during the course of a series of observations on an individual eye, the 
polarity was observed and any changes noted. 
4. Kffects of Heat.—The effects of radiant heat were eliminated by causing 
the light to pass through a spherical double shell of glass, having at least an 
inch of water between the walls. In our earlier experiments we found that 
heat produced immediately an increase in the electro-motive force. It was 
therefore absolutely necessary to eliminate radiant heat. 
I].—EFFects oF LIGHT ON THE EYE OF THE RABBIT REMOVED FROM THE HEAD IMMEDIATELY 
AFTER DEATH. 
Four series of experiments were made on one of the eyes of four individual 
rabbits, as follows :— 
SERIES I—Rasetr’s Eyz.—Source of light, a magnesium lamp. Zero, + 185; 
polarity, + 125; total first deflection, 130°. 










Degrees of Galvanometer scale. 
ce uae ey Coe Ce ae ee ie 
the impact of the impact of removal of the impact of | the removal of 
light. light. light. light. light. 
il 255 259 250 Rise of 4 Fall of 9 
y 250 256 250 Rise of 6 Fall of 6 
3 250 250 245 No rise Fall of 5 2 
4 254 258 254 Rise of 4 Fall of 4 [Fresh trans- 
5 255 258 254 Rise of 3 Fall of 4% | Verse section 
6 185 186 179 Rise of 1 Fall of 7 of nerves 
7 175 175 165 No rise Fall of 10 | Bow made. 
8 165 166 IL 5y5; Rise of 1 Fall of 11 
9 155 157 147 Rise of 2 Fall of 10 
10 150 152 142 Rise of 2 Fall of 10 



The result of this experiment was, that on the impact of light there was an 
average rise of nearly two degrees; the electro-motive force slowly diminished , 
and on the removal of light there was a rapid fall of from jive to seven degrees, 
The rise in this instance on the impact of light, we now know, was owing to the 
action of heat. At this early stage of the inquiry it was deemed necessary to 
focus by a lens the light of the magnesium lamp on the eyeball. 

