164 
CAPTAIN ABNEY ON THE SENSITIVENESS 
Table IV.—Obtained from the Freehand Curves drawn from Table III. 
X. 
Stand¬ 
ard 
curve. 
2-incli 
disc. 
VincE 
disc. 
i 
I-incE 
disc. 
X. 
Stand¬ 
ard 
curve. 
2-incli 
disc. 
4-inch 
disc. 
j-inch 
disc. 
60 
6728 
3-60 
31 
4885 
1-15 
1-43 
1-90 
2-42 
,59 
6621 
3-32 
30 
4848 
1-22 
1-55 
1-97 
2-50 
58 
6520 
3-07 
29 
4812 
1-31 
1-58 
2-06 
2-57 
57 
6423 
2-81 
3-10 
3-65 
28 
4776 
1-41 
1-62 
2-12 
2-62 
56 
6330 
2-60 
2-85 
3-42 
3-90 t 
27 
4742 
1-50 
1-75 
2-18 
2-72 
55 
6242 
2-40 
2-62 
3-18 
3-63 
26 
4707 
1-58 
1-82 
2-35 
2-82 
54 
6152 
2-20 
2-40 
2-95 
3-40 
25 
4675 
1-66 
1-90 
2-43 
2-92 
53 
6074 
2 04 
2-20 
2-73 
3-20 ' 
24 
4634 
1-75 
2-02 
2-52 
2 97 
52 
5996 
1-87 
2-05 
2-55 
3-03 
23 
4608 
1-83 
2-07 
2-60 
3-02 
51 
5919 
1-70 
1-87 
2-40 
2-85 
22 
4578 
1-91 
2-15 
2-65 
3-07 ' 
50 
5850 
1-54 
1-75 
2-20 
2-72 
21 
4548 
2-00 
2-20 
2-70 
.3-15 
49 
5783 
1-37 
1-57 
2-07 
2-57 
20 
4517 
2-05 
2-28 
2-77 
3-20 
48 
5720 
1-25 
1-45 
1-95 
2-42 
19 
4488 
2-09 
2-30 
2-82 
3-27 
47 
56.58 
1-12 
1-35 
1-85 
2-37 
18 
4459 
2-14 
2-35 
2-90 
3-32 
46 
5596 
1-02 
1-25 
1-75 
2-25 
17 
4437 
2 20 
2-40 
2-95 
3-40 
45 
5538 
0-93 
1-17 
1-65 
2-17 
16 
4404 
2-25 
2-50 
3-00 
3-47 
44 
5481 
0’87 
1-10 
1-57 
2-09 
15 
4377 
2-.30 
2-54 
3-06 
3 53 
43 
5427 
0-83 
1-07 
1-53 
2-05 
14 
4349 
2-34 
2-57 
3-15 
3-58 
42 
5373 
0-82 
1-05 
1-52 
2-02 
13 
4323 
2-38 
41 
5321 
0-815 
1-045 
1-52 
2-02 
12 
4296 
2-43 
; 
40 
5270 
0-82 
1-U5 
1-52 
2-03 
11 
4271 
2-48 
39 
5221 
0-825 
1-05 
1-53 
2-05 
10 
4245 
2-52 
38 
5172 
0-84 
1-07 
1-57 
2-07 
9 
4221 
2-57 
37 
5120 
0-86 
1-09 
1-.58 
2-08 
8 
4197 
2-63 
36 
5085 
0-88 
1-10 
1-60 
2-10 
7 
4174 
2-69 
! 
35 
5043 
0-91 
1-15 
1-65 
2-14 
6 
4151 
2-75 
34 
5002 
0-95 
1-20 
1-70 
2-20 
5 
4131 
2-80 
33 
4963 
1-00 
1-25 
1-77 
2-27 
4 
4106 
2-87 
i 
32 
4924 
1-07 
1-35 
1-83 
2.35 
These curves are shown on the diagram, fig. 4, and it wull be evident that within 
the limits of error of observation they are parallel to one another. Had the same 
intensity of original light been used in these experiments as with the standard 
curve (viz., had the intensity of the light at D been equal to 1 amyl acetate lamp), 
Curve I. would have been superposed on Curve V., which is the curve of the 
standard extinction. The intensity of the D light actually employed was very 
closely of an amyl acetate lamp. The curves being very nearly parallel to 
one another show that the light has to be proportionally reduced throughout to 
cause extinction, and further that the smaller the angular aperture of the disc the 
less the reduction in the original intensity has to be. A reference to the results of 
further experiments, to be shortly given, will show that their distance apart has 
been correctly derived. As it might happen that the extinction of a point of light 
differed from one of very sensible size, a disc '012 inch and subtending an angle 
of only 1' 29" was observed. The intensity of the spectrum had to be much 
