TOTAL DAYLIGHT AT KEW AND PARA. 
561 
horizon, the disturbing phenomena of opalescence come into play, and the values of the 
further and yet undetermined terms of the expression become so large as materially to 
affect the result. It is only in the case of the Heidelberg observations that the first 
terms of the series express the relation as low as 8° of altitude, and this is to be explained 
by the fact that the observations at Heidelberg were made at an elevation of 1900 feet 
above the sea-level, and therefore at a situation above a great portion of the denser 
layers of the atmosphere in which the phenomena of opalescence are most marked. 
The curves on fig. 4, Plate XXII., show the rise and fall of monthly chemical intensity 
with the hour of the day for the months of January, February, and March 1867, and 
April, May, and June 1865 ; those on fig. 5, Plate XXII., give the same for the last six 
months of 1865. Figs. 6 and 7 show the same for the twelve months of 1866. 
The mean monthly integrals of chemical intensity for each month from April 1865 
to April 1867, as obtained from these curves, are contained in the first column of the 
following Table. In the second column are given approximations to this integral 
obtained by taking the average of the daily means as given on Table II. (pp. 557 and 558). 
The third column contains the average amount of moisture for the month, in grains per 
cubic foot ; the fourth the relative humidity for the month ; the fifth the average amount 
of cloud at the times of observation; and the sixth the relation between the number 
of observations on which the sun was overcast (=1) and those made in sunshine. 
Table IV. 
Date. 
Chemical Intensity. 
Humidity. 
Cloud. 
L 
II. 
III. 
IV. 
V. 
VI. 
1865. 
overcast =1. 
April 
97-8 
77-1 
3-32 
0-71 
4-1 
1-9 
May 
117-8 
98 -6 
3-63 
0-72 
6-3 
0-5 
June 
82-3 
83-9 
4-23 
0-73 
4-5 
1-6 
July 
114-4 
105-6 
4-82 
0-74 
6-0 
1-0 
August 
88-9 
84-2 
4-50 
0-78 
6-9 
0-6 
September 
107-8 
114-6 
4-81 
0-7 2 
2-4 
3-6 
October 
23-4 
30-4 
3-68 
0-83 
4-0 
1-9 
November 
17-8 
13-2 
3-12 
0-85 
6-7 
0-5 
December 
8-0 
2-98 
0-88 
7-5 
0-3 
1866. 
January 
15-0 
15-9 
2-82 
0-85 
6-0 
0-5 
February 
24-3 
24-2 
2-63 
0-81 
6-4 
0-5 
March 
34-5 
30-6 
2-49 
0-81 
5-6 
0-4 
April 
52-4 
49-9 
3-02 
0-80 
6-3 
0-7 
May 
78-9 
70-0 
2-83 
0-67 
5-0 
0-8 
June 
92-3 
86-1 
4-52 
0-76 
6-6 
1-0 
July 
106-9 
111-9 
4-33 
0-73 
6-0 
0-9 
August 
94-5 
95-2 
4-29 
0-74 
. 7-2 
0-5 
September 
70-1 
100-3 
4-13 
0-83 
6-4 
0-7 
October 
29-5 
40-2 
3-82 
0-88 
6-3 
0-7 
November 
15-6 
17-7 
2-96 
0-83 
5-3 
0-9 
December 
14-0 
3-09 
0-88 
6-9 
0-4 
1867. 
January 
13-0 
8-3 
0-86 
7-8 
0-3 
February 
21-7 
17-5 
2-86 
0 c 82 
7-2 
0-4 
March 
30-6 
27-0 
2-33 
0-83 
7-7 
0-2 
