154 MR. JOSEPH BAXENDELL ON SOLAR RADIATION. 



Combining, now_, the two series of ratios, and taking the 

 means of the two values given for each of the three years 

 1862-64, we have, finally, the following series of corrected 

 ratios all referred to the same scale, and therefore strictly 

 comparable with each other. I have added for compari- 

 son the number of groups of solar spots observed in each 

 year by Schwabe : — 





Ratios. 



Number of 



groups of 



solar spots. 



i8eq 



2'33 



2-57 

 2*17 



174 

 1-64 

 r6i 



i'57 

 117 



205 

 211 

 204 

 160 

 124 

 130 



93 

 45 



i860 



1861 



1862 



186-: 



1864 



186c 



1866 





The curves laid down from these two series of numbers 

 present so close a resemblance in their general form, that 

 it seems impossible to resist the conclusion that the causes 

 which influence the frequency of solar spots also produce 

 corresponding changes in the calorific intensity of the 

 sun^s rays. 



In addition to the conclusions dra^Ti from the discus- 

 sion in the first part of this paper we have now the fol- 

 lowing : — 



1. The power of the atmosphere to absorb the heating 

 rays of the sun is much greater in the summer than in the 

 winter months, and depends apparently upon the amount 

 of aqueous vapour which it contains. 



2. Clouds and haze are less prevalent during the day, 

 or their power to intercept the heating rays of the sun is 

 less active in the spring and autumn than in the winter 

 and summer months. 



3. Observations of solar radiation made with a black- 

 bulb thermometer, to be of value, ought to be taken with 



