39 
other, and that the annual values of the solar radiation 
might bear a constant ratio to the corresponding values of 
the oscillations of mean daily temperature. The annual 
sums and mean daily values of the oscillations of mean 
daily temperature at Oxford for the six years, and the corre- 
sponding ratios, were therefore calculated, and found to be 
as follows : — 
Annual Sums. 
O 
Daily Means, 
o 
Ratios. 
1859 .... 
1182*3 .... 
3-24 
.... 3-96 
1860 .... 
953-0 .... 
2-60 
.... 4T4 
1861 .... 
1054-9 .... 
2-89 
.... 3-88 
1862 .... 
1043-4 .... 
2-85 
.... 3-28 
1863 .... 
1198-4 .... 
3-28 
.... 2-98 
1864 .... 
...... 1158-0 .... 
3-17 
.... 3-09 
The numbers in the last column showed that the ratio 
was not even approximately constant, but that, on the con- 
trary, it was subject to considerable change. I therefore 
concluded that the calorific intensity of the sun’s light was 
also subject to variation; and a glance 
at the course of the numbers at once 
suggested that this variation would be 
found to follow that of solar spot fre- 
quency. Referring to Schwabe’s obser- 
vations of the solar spots, we have the 
following numbers of groups observed 
by him : — 
1859 
205 
1862 
.... 160 
I860 
211 
1863 
124 
1861 
204 
1864 
130 
A projection of these numbers, and of 
the corresponding ratios of solar radia- 
tion to the oscillation of mean daily 
temperature is shown in diagram B; 
No. 1 is the curve of sun spot fre- 
quency, and No. 2 that of the ratios ; 
and it will be seen that the similarity 
