OF THE RETINA TO LIGHT AND COLOUR. 
193 
Fig. 18. 
An iso-lume. 
Other modes of measurement were tried, and the results agreed very fairly inter 
se. The following iso-lumes were taken only in four directions, viz., two in the 
horizontal and two in the vertical (see fig. 19). 
Table XXIY. 
Light reflected 
from grey disc 
when 
white = 100. 
Luminosity in 
powers of — 2. 
Temporal 
reading. 
Nasal reading. 
Upper vertical 
reading. 
Lower vertical 
reading. 
60 
2-74 
12 
9 
8 
9 
38-5 
2T0 
22 
17 
12 
13 
25-5 
1-51 
32 
28 
16 
18 
16-8 
0-90 
43-5 
33 
22 
24 
13-5 
0-31 
51 
40 
28 
28 
11-5 
0-00 
60 
44 
33 
34 
Comparing these readings on the temporal and nasal sides, they agree, as well as 
could be expected from the nature of the observations, wdth the colour field curves. 
VOL. cxc. —A. 2 c 
