OF THE RETIXA TO LIGHT AND COLOUR. 
189 
In connection with this it may be well to quote another observation made direct 
for the purpose of ascertaining the luminosities of ditferent colours required to give 
equal colour fields. The different parts of the spectrum were observed on the retina 
at 25° from the axis on the temporal side, and the luminosities reduced by the 
annulus till the colour disappeared. The readings were somewhat difficult to make, 
but the mean gives the table following. (See fig. 16.) 
Table XX. 
t I. 
Scale No. 
II. 
\ 
III. 
Mean value 
of reading 
of annulu.s. 
IV. 
Value of 
light when 
0 ° = 100. 
V. 
Luminosity 
of spectrum. 
VI. 
Col. V. 
X Col. IV. 
100 . 
VII. 
Col. VI. 
Max. = 100. 
60 
6728 
90 
16-2 
3-5 
•6 
1-3 
58 
6520 
112 
10-9 
12 5 
1-4 
31 
56 
6330 
120 
9-2 
27-5 
2-5 
5-5 
54 
6152 
118 
9-0 
43-0 
3-8 
8-4 
52 
5996 
108 
11-8 
61-0 
7-2 
15-2 
50 
5850 
93 
16-0 
79 0 
12-6 
28-5 
48 
5720 
72 
19-6 
85-0 
16-7 
37-5 i 
46 
5596 
55 
33-7 
81-0 
27-3 
62-0 1 
44 
5481 
37 
48 
72'5 
34-8 
79-0 ! 
42 
5373 
19 
70 
62-5 
437 
98-0 
40 
5270 
8 
85 
52-0 
43-2 
970 
38 
6172 
5 
90 
41-5 
37-3 
84-5 
36 
5081 
4 
93 
33-5 
31-1 
70-0 
34 
5002 
8 
85 
26-5 
22-5 
510 
32 
4924 
17 
65 
21 
13-6 
31-0 
30 
484*8 
43 
43 
16-5 
71 
15-8 
28 
4776 
86 
18-3 
13 
2-4 
5-4 
26 
4707 
114 
10-5 
10-5 
1-3 
2-3 
24 
4639 
124 
8-6 
8-2 
71 
16 
22 
4578 
120 
9-2 
6-3 
•58 
1-27 
20 
4517 
108 
11-8 
5-0 
•50 
1-30 
18 
4459 
97 
14-7 
4-0 
•58 
1-27 
16 
4349 
86 
18-3 
31 
■57 
1-25 
At the time when these results were obtained an experiment was also made by 
the same eye to determine the variations in the fields for four different colours when 
the intensity was altered. The four colours chosen were the same as used in many of 
the experiments made with my own eyes. The fields were taken in the horizontal 
direction, and on the nasal and temporal sides. As the light was varied for each 
colour, in order that readings up to about 60° might be obtained, the fields for the 
rays are not comparable with each other. Each field must be considered by itself 
