553 
ON COLOUR PHOTOMETRY. 
character and in amount. What is M.’s dominant sensation is not quite apparent, 
for, although he described the light between E and D as “ white ” when of ordinary 
intensity, yet he averred that it always appeared ruddy at the moment of extinction. 
Table YII.—P.’s Curves.' 5 '' 
I. 
II. 
III. 
IV. 
V. 
VI. 
VII. 
Scale 
number. 
Wave¬ 
length. 
Mean reading 
of extinction in 
millionths of 
original 
luminosity. 
Adopted 
reading in 
millionths of 
original 
luminosity. 
Persistency 
curve 
680 
P.’s 
luminosity 
curve. 
Absolute 
luminosity 
of extinction 
IV. x VI. 
14 ’ 
ad. reading 
52 
5996 
68 
68 
10 
7- 
34 
50 
5850 
35 
35 
19-4 
19' 
47-5 
48 
5720 
17 
17 
40 
39 
473 
46 
5596 
10-2 
10 
68 
65 
46-4 
45 
5538 
9-3 
9-0 
76 
76 
48-8 
44 
5481 
8-0 
87 
84 
90 
52-8 
42 
5373 
7-2 
7-2 
94-5 
98 
50-3 
40 
5270 
67 
6-8 
100 
99 
487 
38 
5172 
7-2 
7-0 
97 
97-5 
487 
36 
5085 
8-05 
77 
90 
90 
49-5 
34 
5002 
8-05 
8-4 
81 
80 
47-9 
32 
4924 
9-9 
9-8 
69 
65 
45'5 
30 
4848 
13 2 
12-5 
54 
50 
44-6 
28 
4776 
13-9 
15-0 
45-3 
36 
38-6 
27 
4742 
16-8 
17-0 
40 
31-5 
38-2 
26 
4707 
21-6 
20-5 
32 
26-5 
38-8 
24 
4639 
30 
27 
25 
19-5 
37-6 
22 
4578 
36 
35 
19 
14 
35 
20 
4517 
42 
45 
15-5 
10 
32-2 
16 
4404 
79 
79 
8-5 
5-5 
312 
10 
4245 
180 
190 
3-6 
2-5 
32-2 
6 
4151 
270 
270 
27 
* In this and the next two Tables tbe intensity of the illumination of the D ray before reduction is 
equal to that of an amyl-acetate lamp at one foot from a screen. The figures in Col. VII. are in 
millionths of the illumination of an amyl-acetate lamp at one foot distant, every ray being made of that 
intensity. 
4 B 
MDCCCXCIL-—A. 
