456 
CAPT. ABNEY AND MAJ.-GEN. EESTING ON COLOUR PHOTOMETRY. 
affect both alike, and comparisons are easily made. Of course for the electric light 
the same procedure may be had recourse to, and gives the same curve as when the 
candle is used as the comparison-light. 
Table of the luminosity of the solar spectrum taken by new method. 
No. I. — 4th June, 1886 
2 P.M. 
1 
* No. II.- 
-21st July, 1886, 2 p.m. 
Luminosity. 
Luminosity. 
Scale readings. 
Seale readings. 
Comparative apertures 
Beduced 
Comparative apertures 
Beduced 
of rotating disc. 
Intensity. 
of the rotating disc. 
Intensity. 
O 
105 
100 
47-33 
O 
135 
97-8 
47’24 and 46‘77 
100 
95-2 
47-73 and 46-54 
120 
87-0 
48T6 „ 45-97 
90 
87-5 
48-52 „ 45-75 
105 
76-1 
48-61 „ 45-63 
80 
76-2 
49-01 „ 45-35 
97 
70-3 
48-84 „ 45-52 
70 
66-6 
49-41 „ 45-15 
90 
65-2 
49-18 „ 45-40 
60 
57-1 
49-91 „ 44-96 
80 
58-0 
49-64 „ 45-17 
50 
47-6 
50-20 „ 44-70 
70 
50-8 
49-87 „ 45-06 
45 
42-8 
50-40 „ 44-66 
60 
43-5 
50-09 „ 44-83 
40 
38T 
50-60 „ 44-56 
50 
36-3 
50-53 „ 44-60 
35 
33-3 
50-80 „ 44-46 
40 
29-0 
50-76 „ 44-49 
30 
28-5 
50-90 „ 44-42 
30 
21-7 
51-10 „ 44-38 
25 
23-8 
51-09 „ 44-36 
20 
14-5 
51-56 „ 44-26 
20 
19-0 
51-39 „ 44-26 
15 
10-8 
51-90 „ 44-03 
15 
14-2 
51-69 „ 44-16 
10 
7-25 
52-92 „ 43-80 
10 
9-5 
52-28 „ 44-07 
5 
362 
53-S4 „ 43-58 
5 
4-8 
53-27 „ 43-87 
3 
2-17 
54-75 „ 43-35 
2-5 
2-4 
54-46 „ 43-47 
2 
1-45 
55-89 „ 43-01 
1-6 
1-6 
55-65 ,. 43-37 
1 
•72 
57-94 „ 42-67 
•8 
•8 
57-23 „ 43-17 
•330 
•24 
61-59 „ 42-21 
•4 
•4 
59-21 „ 43-00 
Fig. 11 gives the curves drawn from the above tables. 
It should be remarked that from the measurements we have made in London, the 
solar curve varies considerably according to the direction of the wind. A wind from 
the east diminishes the intensity of the blue end of the spectrum—a fact no doubt 
due to the smoke haze which is then prevalent. 
We omitted in our paper to point out the method by which the prismatic spectrum 
curve can be converted into the normal spectrum curve. It will be seen that a 
dl 1 
very approximate curve can be obtained by using —y or — as the factor by which the 
ordinates of the curves in the former can be reduced to the latter. 
* This table gives a fair idea of the luminosity of the solar spectrum in July of this year, the wind 
being in the S.W., and the sky blue. It agrees with other curves taken on different days, and is a 
representative one.—[July 23.] 
