40 
in form of the two curves is remarkably striking, and 
apparently conclusive, as to the connection between the two 
classes of phenomena. 
Assuming that changes in the heating power of the sun’s 
rays follow the course of the changes in solar spot frequency, 
it seemed probable that the ratio of the difference between 
the maximum temperature in the shade and in the sun, to 
the difference between the mean daily temperature, — or 
better, perhaps, the temperature of evaporation, — and the 
maximum temperature in the shade, would also exhibit 
corresponding changes. It will be seen that the following 
results strongly support this view : — 
Max. Temp, in Sun, 
less Max. Temp, 
in Shade, 
o 
Max Temp, in Shade, 
less Mean Temp, of 
Evaporation, 
o 
Ratio. 
1859 .... 
12-85 
1006 
... 1-27 
1860 .... 
10-78 
8-63 
... 1.25 
1861 .... 
........ 1124 
9-52 
... 1-18 
1862 .... 
9-37 
9-28 
... 1-09 
1863 .... 
9-78 
...... 10-38 
... 0-94 
1864 .... 
9-81 
10-57 
... 0-93 
The line No. 3 in diagram B is a projection of these 
ratios. It would probably be better to employ the maximum 
instead of the mean temperature of evaporation, but this is 
not given in the printed observations. 
The mean values of solar radiation given above in the first 
table, aie deduced from observations made on every day in 
the year, and therefore in every possible state of the atmos- 
phere — clear, cloudy, rainy, foggy, calm, stormy, &c. — but it 
was evidently desirable to determine the calorific intensity 
of the sun’s rays on days when the sky was cloudless at the 
time of maximum temperature. The printed observations, 
however, do not always show when this was the case, and 
it became necessary to adopt some arbitrary principle of 
selection. As the one which appeared to me to be least 
