BETWEEN THE SUN’S .ALTITUDE AND CHEMICAL INTENSITY. 
311 
By reference to the calibration Table of the strip the following numbers were found 
to correspond to the above readings. 
Time 3 h 59 111 p.m. Sun’s altitude 35° 25\ 
Observed Chemical Intensity . — 
Direct sunlight. Diffused light. Total daylight. 
0-069 0-138 0-207 
The meteorological conditions of the time of observation were also carefully observed. 
f Dry-bulb thermometer 81 o, 0 F. 
Clouds 0-0. Fine breeze, S.S.W. 
Barometer at sea-level 763-9 millims. 
( Wet-bulb thermometer 69 o, 0 F. 
( Aqueous vapour in 1 cub. ft. 5 -7 grains. 
1 Relative humidity =50. 
One of the 134 sets of observations was made as nearly as possible every hour, and 
they thus naturally fall into seven groups, viz. — 
(1) Six hours from noon, (2) five hours from noon, (3) four hours from noon, (4) 
three hours from noon, (5) two hours from noon, (6) one hour from noon, 
and (7) noon. 
Each of the first six of these groups contains two separate sets of observations, viz. 
those made before noon marked A.M., and those made after noon and marked P.M. 
One of us has already pointed out*, from measurements made at Kew, that the mean 
chemical intensity of total daylight for hours equidistant from noon is the same. That 
this result is a general one is fully borne out by the inspection of the following Tables, 
giving the results of 1 34 series of observations ; the single experiments made at the 
same hour being grouped together, and those of the hours equidistant from noon being 
placed side by side. 
Table I. (1.) 
A.M. 
P.M. 
Expt. 
Date. 
Hour. 
Altitude. 
Sun. 
Sky. 
Total. 
Expt. 
Date. 
Hour. 
Altitude. 
Sun. 
Sky. 
Total. 
li m 
h m 
11. 
6 
6 4 
10 33 
000 
•049 
•049 
19- 
6 
6 0 
11 31 
•000 
•056 
•056 
29 • 
9 
6 6 
10 15 
•001 
•033 
•034 
28. 
8 
6 2 
10 43 
•000 
•041 
•041 
48. 
12 
6 9 
10 20 
•001 
•040 
•041 
40. 
9 
6 0 
10 58 
•000 
•034 
'034 
47. 
10 
6 0 
10 50 
•002 
•050 
•052 
31 08 
•002 
. 122 
•124 
57. 
12 
5 59 
10 22 
•000 
•034 
•034 
67. 
21 
5 51 
10 02 
•000 
•031 
•031 
Means 
10 23 
•000 
•041 
•041 
76. 
22 
6 0 
7 58 
•000 
•031 
•031 
86. 
23 
6 0 
7 20 
•000 
•026 
•026 
97. 
24 
5 47 
9 50 
•002 
•038 
•040 
107. 
26 
5 49 
8 37 
•000 
•031 
•031 
118. 
27 
5 51 
8 04 
•000 
•029 
•029 
128. 
28 
5 53 
7 17 
•000 
•022 
•022 
113 32 
000 
•423 
•427 
Means 
9 28 
•000 
•035 
•035 
* Philosophical Transactions, 1867, p. 558. 
2 t 2 
