840 
Proceedings of Royal Society of Edinburgh. [sess. 
In this way it was possible to examine the action of the 
fluorescent light on the eye. The usual phenomena occurred, but 
the amount of increase with radium on and radium off was only 
about one-eighth part of that produced by light on and light off 
in the same eye in a subsequent experiment. 
Expt. 6. The surface of the mineral was covered with black paper. No 
fluorescence. Still radium on and radium off gave a slight + effect, about 
1 div. Black paper was then placed over the radium. There was still a 
slight effect, about '5 div. 
Expt. 7. Another eyeball placed on pads, so that the cornea faced 
upwards. The mineral was removed. Radium was placed so as to be 
directed to cornea, but lead plate could be interposed ; the usual phenomena 
were detected. A glass slide 1 - 5 mm. thick was placed over eye ; usual 
effects observed, but much smaller. A strip of aluminium 1*5 mm. thick 
was placed over glass slide. Still an effect of 1 div. could be observed with 
radium on and radium off. 
In Expt. 7 it may be assumed that some or most of the /3 rays 
were cut off ; if so, the small effect was due to the y rays. 
The next experiment is adduced as an example of several, 
which appear to indicate that after the influence of radium on an 
eye for a short time the eye becomes more sensitive to the action 
of ordinary light. 
Expt. 8. Eye placed on pads with cornea directed upwards. Radium 
above, in usual position, facing cornea. Yery large resting current, and, by 
means of a shunt, only x^-th part of it was used, represented by 20 divs. on 
scale. With the full current, radium on gave a rise of 5 divs., then a slight 
fall, then a rise of 1'5 divs., and again a slight fall. Radium off gave a rise 
of 3 divs., and then a fall to near the original point. The radium was then 
enclosed in a pill box having the bottom painted black, the radium being 
directed towards the blackened bottom. Radium on, rise of 2 divs. ; radium 
off, rise of 2 divs., and then a fall to 4 divs. below original position. Again, 
radium on, rise of 2 divs., slight fall, rise of 5 divs. ; radium off, rise of 2 
divs., fall to original position. After an interval of three minutes, light 
from the electric lamps was allowed to fall on eye by opening shutter on 
upper surface of blackened box ; a rise of 35 divs., then a slight fall ; light 
off, rise of 5 divs., then fall to original position. The eye was kept in the dark 
for thirty minutes (in the small black box). When the lid was opened, in the 
darkened room, with no electric lamps, there was a rise of 15 divs. ; when 
the lid was closed there was a rise of 1 *5 divs. , and then a fall to the original 
position. This was the most sensitive eye we have ever seen.* 
The next experiment is illustrative of an attempt to exclude the 
* Note by J. G. M‘K. I have seen hundreds of the original experiments 
during the last thirty years, but I have never met with an eye so sensitive as 
this one. 
