162 
CAPTAIX ABNEY ON THE SENSITIVENESS 
as the ordinates, a much more convenient form of curve was obtained. As the angles 
are proportional to the logarithms of the extinction these latter were employed 
instead of the angles themselves, to enable the results obtained with any other wedge 
to be made comparable with those obtained with the new apparatus. For the sake of 
comparing the results of the extinction of the spectrum obtained in the former 
experiments, given in Part III., Colour Photometry, the curve of the extinction for 
the normal eye was converted to a logarithmic curve, and the conversion will be found 
in Table II. 
TxVBLE II.—Extinction by the Centre of the Eye, from Part IIP, “ Colour 
Photometry.” 
1 
Scale 
N umber. 
X. 
Reduction. 
Log. ■ 
' 
Scale 
Number. 
X. 
Reduction. 
Log. 
64 
1 
7217 
55,000 
4-740 
33 
4963 
10-2 
1-009 
63 
7082 
30,000 
4-477 
32 
4924 
11-6 
1-064 
62 
6957 
15,000 
4-176 
31 
4885 
13-6 
1-130 
61 
6839 
7,500 
3-875 
30 
4848 
16-3 
1-212 
60 
6728 
3,750 
3-574 
29 
4812 
20-5 
1-312 
69 
6621 
1,900 
3-278 
28 
4776 
26-0 
1-415 
58 
6520 
1,410 
3-070 , 
27 
4742 
31-0 
1-491 
57 
6423 
650 
2-812 1 
26 
4707 
38-5 
1-585 
66 
6333 
380 
2-579 i 
25 
4674 
46 
1-663 
55 
6242 
272 
2-434 
24 
4639 
56 
1-748 
.')4 
6152 
196 
2-292 
23 
4608 
67 
1-826 
53 
6074 
112 
2-046 
22 
4578 
80 
1-903 ! 
52 
5996 
79 
1-900 
21 
4548 
95 
1-978 ! 
51 
5919 
53 
1-752 
20 
4517 
107 
2-029 
50 
5850 
35 
1-544 
19 
4488 
124 
2-093 
49 
5783 
24 
L-380 
18 
4459 
140 
2-146 
48 
6720 
17 
1-230 
17 
4437 
160 
2-204 
47 
5658 
12-6 
1-100 
16 
44045 
ISO 
2-255 
46 
5596 
10-2 
1-050 
15 
4377 
200 
2-301 
1 45 
5538 
8-6 
0-934 
14 
4349 
220 
2-342 
44 
5481 
7-4 
0-869 
13 
43-23 
240 
2-380 
1 43 
5427 
6-7 
0-826 
12 
4296 
270 
2-431 
1 42 
5373 
6-55 
0-816 
11 
4271 
300 
2-477 
; 41 
5321 
6'5 
0-813 
10 
4245 
335 
2-525 
40 
5270 
6-55 
1 0-816 
9 
42-21 
375 
2-574 1 
39 
5221 
6‘65 
' 0-822 
8 
4197 
430 
2-633 
38 
5172 
6-85 
0-835 
7 
4174 
490 
2-690 
37 
5128 
7-2 
0-857 
6 
4151 
560 
2-748 
: 36 
5085 
7-6 
0 881 
5 
4131 
640 
2-806 
i 35 
5043 
8T5 
0-911 
4 
4106 
750 
2-875 
! 64 
5002 
8-8 
0-944 
When the ordinates of the curves are the logarithms ot the actual values, the 
reduction in intensity of the same ray required to make it invisible under difierent 
conditions is readily seen. Thus, if two such curves are parallel to one another, we 
at once see that the intensities for all colours are proportionally reduced. 
