OF THE RETINA TO LIGHT AND COLOUR. 
167 
The following are the values, iii inches, of the apertures used, and in powers of 2, 
and the angles they subtended at the distance from which they were observed :— 
Diameter in inches. 
Angles subtended. 
Value in powers of 2. 
2-0 
O 1 // 
4 11 0 
+ 1-0 
1-50 
3 8 0 
+ 0-6 
0-94 
1 57 0 
-0-09 
0-725 
1 30 0 
-0-48 
0-525 
15 0 
-0-93 
0-42 
0 52 35 
-1-25 
0-35 
0 43 43 
-1-52 
0-30 
0 37 33 
-1-74 
0-17 
0 21 17 
— 2-56 
0-086 
0 10 46 
-3-56 
0-036 
0 4 30 
-4-81 
0-012 
0 1 30 
-6-40 
These diaphragms were placed in front of the ground glass, and the light from the 
discs thus formed, extinguished. In the first set of experiments, the pure colours of 
the spectrum were employed ; whilst in the others, ordinary lamp light and lamp 
light screened with different colour glasses or solutions were used, and identical 
results were found in all cases. The following tables are made from the mean 
readings, and the diagram shows them plotted :— 
