902 PEOFESSOE BUNSEN AND DE. H. E. EOSCOE’S PHOTO-CHEMICAL EESEAECHES. 
Table XI. 
0. 
. 
-1. 1 
90 
31370 
80 
151400 
70 
246800 
60 
316700 
50 
361300 
40 
381100 
35 
382500 
30 
377500 
Hence we obtain 
Wi=27760+808490cos<p-~469960cos^<p, (9.) 
by help of which the following Table (XII.) is calculated. The chemical action (wj 
effected by the dijffuse light from the whole sky is here expressed, not in units of light, 
but in degrees of light, each of which is equal to 10,000 units of light. 
Table XII. 
•P- 
J 
Wl- 
<p. 
Wv 
Wr 
w^. 
31 
38'29 
41 
37-60 
51 
35-45 
61 
31-17 
71 
24-22 
81 
14-30 
32 
38-26 
42 
37-47 
52 
35-11 
62 
30-60 
72 
23-37 
82 
13-15 
33 
38-24 
43 
37-31 
53 
34-78 
63 
30-00 
73 
22-4^ 
83 
11-95 
34 
38-21 
44 
37-14 
54 
34-40 
64 
29-38 
74 
21-56 
84 
10-72 
35 
38-14 
45 
36-96 
55 
34-02 
65 
28-73 
75 
20-62 
85 
9-47 
36 
38-08 
46 
36-74 
56 
33-61 
66 
28-06 
76 
19-64 
86 
8-19 
37 
38-01 
47 
36-53 
57 
33-17 
67 
27-34 
77 
18-64 
87 
6-88 
38 
37-93 
48 
36-30 
58 
32-72 
68 
26-61 
78 
17-60 
88 
5-54 
39 
37-85 
49 
36-02 
59 
32-22 
69 
25-84 
79 
16-53 
89 
4-17 
40 
37-72 
50 
35-75 
60 
31-70 
70 
25-05 
80 
15-43 
90 
2-77 
These degrees of light (wj express the chemical action which the diffuse light from 
the whole sky effects during one minute upon the horizontal unit of area on the earth s 
surface when the corresponding zenith-distance of the sun is <p. The cuiwe (fig. 10, 
Plate LV.) represents the relation of this chemical action to the sun’s zenith-distance, 
marked as abscissae. The points on the figure denote the values of Table XL, from 
which the curve is derived ; their approximation to the line shows how closely the results 
obtained by calculation agree with the observed numbers. 
By means of formula (5.), cos ip=cos ^ cos^ cos i^+sin ^ sinj9, already given, and either 
formula (9.) or Table XII., the illuminating effect of the cloudless sky at a given locality 
and at a given time, can be calculated. As an example of this method, we give the 
results of the calculation of the chemical illuminating effect produced by the cloudless 
sky during the various hours of the day on the vernal equinox at Cairo, Naples, Heidel- 
berg, Manchester, Petersburg, Peykiavik, and Mehille Island. 
