558 
CAPTAIN W. DE W. ABNEY AND MAJOR-GENERAL E. R. FESTING 
to bring the maximum to 100. This curve (fig. 45), that of the monochromatic sensa¬ 
tion, and the persistency curve are tabulated together in Table X., to show how closely 
they agree. Here we have a proof that the normal eye is as little sensitive to the red 
end of the spectrum formed from a very much reduced light as those of the two brothers 
when ordinary light is used. It must be remarked, however, that all colour was not 
entirely absent, though it was very considerably reduced in saturation. The measure¬ 
ments were made with some trouble at first, owing to the inclination of the eye to 
direct its axis to some point other than the centre of the patch where the white strip 
and the colour strip touch one another. The diversion of the axis of the eye in some 
cases made the colour more luminous, and in other cases less so, than it did when the 
eye was properly directed, as might be surmised from the luminosity curves of light 
of ordinary intensity. By reducing the light in less degrees it became possible to 
obtain curves of luminosity which agreed very closely with those of the different 
degrees of red blindness (that is, where the spectrum is shortened at the red end), of 
which we have had many cases to try. As already pointed out, the outer part of the 
retina of our own eyes is really in one stage of red blindness, having a slightly 
shortened spectrum. 
Table X.—Luminosity of Spectrum Reduced in Intensity so that D = T 3 i 2 r 5 amyl 
lamp 1 foot distant. 
Scale number. 
Mean reading. 
Mean reading, 
reduced to 100 
ruax. 
P. and Q.’s read¬ 
ings, 100 max. 
Persistency curve 
for the centre of 
the eye. 
55-6 
•5 
•6 
2 
2 
53'6 
5-5 
7-0 
3-6 
3-6 
51-6 
13 
167 
8 
8 
49-6 
23 
29-7 
22 
22 
47-6 
40 
50-0 
44 
44 
45-6 
57 
71-2 
69 
69 
43-6 
70 
87-5 
93 
93 
41-6 
79 
98-7 
100 
995 
396 
78 
97-5 
99-5 
98-5 
37-6 
74 
92-5 
96 
93 
35-6 
66 
82-5 
89 
84 
33-6 
55 
68-7 
77-5 
71 
31-6 
44-5 
55-2 
61 
53-5 
29-6 
35 
437 
45-5 
365 
27-6 
24 
30-0 
335 
24 
25-6 
17 
21-7 
25 
16 
23-6 
13 
16-7 
18 
10 
21-6 
10 
12 5 
13 
8 
19-6 
8 
io-o 
9-5 
6 
13-6 
3 
37 
4-2 
3 
9-6 
2 
2-5 
25 
2 
i 
