98 
might be necessary in a more exact inquiry in consequence 
of equal increments in the difference between sun and shade 
temperatures not corresponding exactly to equal increments 
of calorific intensity of the sun’s rays. This table gives for 
every fifth degree of altitude the calorific intensity of sun- 
light, the intensity of the light on entering the earth’s 
atmosphere being taken =1. If the rate of emission of heat 
from the sun were constant, and change of season exercised 
no influence on the absorptive power of the atmosphere, the 
quotient obtained by dividing the mean value of solar radia- 
tion on clear days in any month, by the number in this 
table corresponding to the sun’s meridian altitude in the 
middle of the month, would be a constant quantity. The 
results given in the following table will however show that 
according to the Oxford observations this is by no means 
the case : — 
1 
Mean Amount of 
Solar Radiation 
on Clear days. 
1 
Meridian 
Altitude of the 
Sun on the 15th 
of the Month. 
Proportion of 
Light 
Transmitted. 
Number in 
First Column 
divided by 
Number in 
Third Column. 
January 
13-5 
17 6 
*37 
36-5 
February 
17-6 
25 32 
*51 
34-5 
March 
17-8 
36 3 
*61 
29 2 
April 
203 
47 57 
•68 
29-8 
May 
19-2 
57 4 
•71 
270 
J une 
181 
61 34 
•72 
25*1 
July 
19-2 
59 50 
•72 
26-7 
August 
196 
52 23 
•69 
28-4 
September 
200 
j 41 22 
•65 
30-8 
October 
18-1 
29 48 
•56 
32-3 
November 
15-6 
19 48 
•43 
363 
December 
130 
1 14 59 
•33 
39-4 
The numbers in the last column show that the power of 
the atmosphere to absorb the heating rays of the sun is 
much greater in the summer than in the winter months, the 
maximum effect taking place in the month of June, when the 
