900 PEOFESSOE BTHSTSEN AND DE. H. E. EOSCOE’S PHOTO-CHEMICAE EESEAECBffiS. 
Table IX. 
Number of 
experiment. 
True solar time. 
•v. i 
Sun’s zenith- i 
distance. j 
Action in 
scale-divisions. 
Chemical brightness in units of i 
light of a piece of zenith-sky 1 
of the whole sky. j 
h 
m 
1 
0-0 
1 
1856, 
18 
Oct. 
6 
46 
A.M. 
90 
4 
0-000 
2 
6 
51 
A.M. 
89 
17 
0-63 
23-2 
3 
6 
55 
A.M. 
88 
39 
0-88 
32-5 
4 
7 
3 
A.M. 
87 
25 
1-92 
71-1 
5 
7 
7 
A.M. 
86 
48 
2-19 
81-0 ■ 
6 
7 
17 
A.M. 
85 
16 
3-15 
116-3 
7 
7 
23 
A.M. 
84 
22 
3-42 
126-5 
8 
7 
41 
A.M. 
81 
41 
4-81 
177-6 
9 
8 
5 
A.M. 
78 
14 
6-01 
222-2 
10 
8 
11 
A.M. 
77 
25 
6-40 
236-8 
11 
8 
33 
A.M. 
74 
27 
7-82 
289-2 
12 
9 
8 
A.M. 
70 
7 
8-56 
316-6 
13 
3 
53 
P.M. 
• 77 
58 
6-44 
200-8 1 
14 
1858, 
23 
July. 
7 
30 
A.M. 
60 
21 
6-94 
485-8 
15 
7 
52 
A.M. 
56 
47 
7-93 
555-1 
16 
8 
52 
A.M. 
47 
21 
10-06 
704-2 
17 
9 
46 
A.M. 
39 
36 
11-82 
827-4 
18 
10 
15 
A.M. 
36 
0 
13-04 
912-8 
19 
10 
48 
A.M. 
32 
37 
13-72 
960-4 
20 
11 
20 
A.M. 
30 
22 
15-26 
1068-2 
gl 
12 
0 
A.M. 
29 
18 
16-04 
1122-8 
22 
1858, 
5 
Aug. 
7 
46 
A.M. 
60 
1 
7-59 
531-3 
23 
8 
11 
A.M. 
56 
1 
8-65 
605-4 
24 
8 
51 
A.M. 
49 
62 
9-79 
685-3 
9 
17 
A.M. 
46 
5 
i 10-32 
722-4 
In experiniGnts 1 to 13 tlic following data woro employed for tlie calculation of the 
brightness, expressed in units of light, found in the 6th column: K=1’777, L~l'4o, 
N~l*031, ?i=:2-249, ^=0™-0530, r=l™-474. In the other experiments these values 
remained constant, except £^=0“*059, and r=2“*260. 
The chemical brightness (w) of the circle of zenith-sky equal in area to i o\) P^i’t of 
the whole heavens, as seen in the last column of the preceding Table, can be repie- 
sented as a function of the corresponding zenith-distance of the sun (<p), with sufficient 
accuracy by help of the following equation, 
w^ll82-7-13-857+^^, ' . . . (7.) 
in which the numbers are calculated from all the observations according to the method 
of least squares. From this equation Table X. is calculated. It gives for every zenith- 
distance of the sun from 20° to 90° the amount of light, expressed in light-units, which 
falls perpendicularly upon a unit of area on the earth’s surface, from a portion of zenith- 
sky equal to P^^^ of the whole heavens. 
