102 
ment of the mean monthly values of solar radiation we 
have the following table : — 
( 
Mean Monthly 
Solar 
Radiation. 
Mean 
Temperature 
of Air less Mean 
Temperature 
of Evaporation. 
| 
Ratio. 
1 
January 
5-51 
1-31 
4-20 
February 
916 
1-75 
523 
March 
1008 
2-36 
4-27 
April 1 
13 23 
300 
4-41 
May 
12-90 
3-78 
3-41 
June 
12-93 
3-43 
3-76 
July 
13-81 
4-15 
3-32 
August 
1403 
3-73 
3-76 
September 
13-71 
2-81 
4-88 
October 
966 
2-05 
4-71 
November 
8-00 
1-41 
5-67 
December 
4-50 
115 
3-91 
Before the true import of the numbers in the last column 
can be clearly understood, it will be necessary to apply cor- 
rections for the changes of meridian altitude of the sun in 
the different months of the year, and employing for this 
purpose the table in the article on climate in the Encyclo- 
paedia Britannica already referred to, we obtain the follow- 
ing corrected numbers : — 
January 
1-59 
1 
July 
2-39 
February 
2-66 
August 
2-59 
March 
2-60 
September 
3-17 
Aoril 
300 
October 
2-63 
May 
2-42 
November 
2-44 
June 
2-70 
December 
1-29 
The highest values occur in April and September, the 
months in which the diurnal oscillations of the declination 
magnetometer are greatest, and the general course of the 
numbers indicates that clouds and haze are less prevalent, 
or less dense, or their power of absorbing the heating rays 
