299 
1900-1901.] Prof. Knott on Solar Radiation. 
the relative solar radiation falling on unit horizontal surface, the 
unit radiation being the quantity that would have fallen normally 
on a square centimetre had there been no atmospheric absorption. 
The data from which these curves were constructed are given in 
the following table. 
Table showing the time in hours reckoned from culmination at 
ichich for given values of the sun's declination , as shown in the 
tojp row , the radiation crossing unit horizontal surface in lat. 
33° K. has value as shown in the first column . 
R. 
+ 23° 72' 
+ 20 
+ 12 
0 
-12 
-20 
- 23° 27' 
Sun’s decl. 
•703 
0 
•675 
0 
*638 
0 
•606 
1*83 
1-67 
I'll 
•549 
0 
•512 
2-71 
117 
1 
•427 
0 
o 
•333 
0 
•331 
4 
3*88 
3-57 
2*82 
1-96 
o 
•302 
0 
s 
*245 
4-53 
1-46 
H 
*0914 
5*51 
5*44 
5-11 
4*6 
3*98 
3*49 
3*21 
•06 
5 82 
0073 
6*44 
6*28 
5-94 
5-43 
4-86 
4*44 
4-24 
0 
7-06 
6-89 
6*53 
6 
5-47 
5-08 
4-9 
From these seven curves we can estimate the areas, and thus 
evaluate the integral j Rdt from culmination to sunset or from 
sunrise to culmination. The results are given in the following 
small table, in which the first column contains the sun’s declina- 
tion, and the second the relative radiation reaching unit horizontal 
surface, the unit of time involved being the minute. 
Declination. 
Half-daily heating 
(relative). 
+ 23° 27' 
158*34 
+ 20 
150-57 
+ 12 
135-00 
0 
105*15 
-12 
73-8 
-20 
54-0 
-23 27 
46-8 
