55 G 
CAPTAIN W. DE W. ABNEY AND MAJOR-GENERAL E. R. FESTING 
Table IX.—H. R’s Curves. 
I. 
II. 
III. 
IY. 
Y. 
YI. 
I I 
VII. 
Scale 
number. 
Wave¬ 
length. 
Mean reading 
of extinction 
in millionths 
of original 
luminosity. 
Adopted 
reading in 
millionths of 
original 
luminosity. 
Persistency 
curve 
590 
Luminosity 
curve. 
r 
Absolute 
luminosity 
of extinction ; 
IY. x VI. 
ad. reading 
CO 
57 
6423 
1200 
1200 
•49 
5 
125 
56 
6330 
900 
850 
•69 
7 
124 
55 
6242 
500 
550 
1-07 
10 
115 
54 
6152 
250 
250 
2-36 
17 
88 
53 
6074 
# . 
150 
3-93 
25 
78 
52 
5996 
90 
90 
6-56 
35 
66 
51 
5919 
60 
45 
13-1 
47 
44 
50 
5850 
27 
27 
21-8 
57 
32 
48 
5720 
18 
15 
39-3 
66 
21 
46 
5596 
10 
10 
59 
69 
14 
44 
5481 
9-3 
8 
73-8 
64 
11 
42 
5373 
65 
6'2 
95-1 
56-5 
7 
40 
5270 
5-9 
5-9 
100 
45 
5-5 
38 
5172 
6 
6 
98-3 
32 
4 
36 
5085 
. , 
6-6 
89-4 
20 
2-7 
35 
5043 
7 
7-2 
81-9 
16 
2-4 
34 
5002 
# , 
8 
73-8 
12-5 
21 
32 
4924 
10 
9-6 
61-5 
8 
1-6 
30 
4848 
11-5 
12 
49-2 
6 
1-5 
28 
4776 
14-5 
14-5 
40-7 
5 
P5 
26 
4707 
20 
17 5 
337 
4 
1-5 
24 
4639 
20 
22 
26-8 
3 
1-4 
22 
4578 
, , 
30 
19-7 
2-4 
1-5 
18 
4459 
55 
57 
10-4 
1-3 
1-5 
14 
4349 
115 
115 
51 
•7 
1-7 
10 
4245 
, , 
160 
3-7 
•5 
1-7 
6 
4151 
200 
200 
2-9 
•4 
1-7 
§ L .—Luminosity of a Spectrum produced by Feeble Light. 
Having found that the persistency curve was apparently and presumably the same 
as the luminosity curve of the two persons who had but one colour sensation, it almost 
followed that if the beam of light producing the spectrum were sufficiently reduced 
its curve of luminosity would approach these. An experiment was therefore made. 
The reference beam was introduced into the measuring box already described (fig. 36), 
and, when uninterrupted by the sectors, had a luminosity of T 3 V 5 °f an amyl 
lamp at one foot off. The beams from the spectrum of the colour patch apparatus 
were also introduced into the apparatus so that they fell as before on S. The luminosity 
of the different rays was taken in the ordinary manner interposing the rotating 
sectors in the reference beam. The following results were obtained (see Table XI), 
the mean of the readings being given. This mean in Column III. is multiplied by 1*25 
