ON SOLAR RADIATION. 131 



ment of temperature ; but observing that the time of mini- 

 mum corresponded exactly with that of maximum in the 

 curve laid down from the numbers given in a table which 

 I communicated to the Physical Section on the 5th of 

 March 1863, showing the monthly sums of the oscillations 

 of mean daily temperature at Greenwich during the thir- 

 teen years 1848-60, and also the mean daily values for 

 the diflPerent months, and that the time of maximum 

 agreed nearly with that of minimum disturbance of mean 

 daily temperature, it occurred to me that the two pheno- 

 mena might be closely connected with and dependent upon 

 each other, and that the annual values of the solar radia- 

 tion 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 corresponding ratios, were therefore calculated, and 

 found to be as follows : — 



Annual sums. Daily means. Eatios. 



o o 



1859 1182*3 3*24 3-96 



i860 953'o ^'60 4*14 



1861 io54'9 2-89 3*88 



1862 1043*4 2*85 3*28 



1863 1198-4 3-28 2-98 



1864 1158-0 317 309 



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 variations ; and a glance at the course of 

 the numbers at once suggested that this variation would 

 be found to follow that of solar-spot frequency. Referring 

 to Schwabe's observations of the solar spots, we have the 

 following numbers of groups observed by him : — 



1859 205 



i860 211 



1861 204 



1862 160 



1863 124 



1864 130 



k2 



