50 



earth became intensified and more direct, and this I have 

 called " direct sun-power." 



This "direct sun-power" is very different from the difference 

 of the power of solar radiation in summer and in winter, in 

 latitudes of the middle of the temperate zones. For whilst 

 in our latitude the difference between the extreme summer 

 and winter mean temperatures amounts to about 90 per cent 

 of the winter temperature, the difference between the ex- 

 treme " direct sun-power " of summer and winter is 1,300 

 per cent of that of the winter. 



The following table represents this " direct sun-power " 

 under assumed numbers between O'O and 36 '0. And these 

 numbers were assumed because in no case hitherto has the 

 difference of the readings of the two thermometers exceeded 

 36 deg. Fahr. The numbers therefore in the following table 

 represent the relative values of this " direct sun-power " for 

 the last five years reduced to their mean values for each 

 succeeding three months of the year. 



From the above table it will be seen that the solar ra- 

 diating " direct sun-power" was far the greatest throughout 

 the year 1883. 



That this energy becomes potent according to the increase 

 of solar activity will appear if the values of the above table 

 be compared with the mean values in degrees of Fahr. of 

 ordinary solar radiation as registered by a black bulb ther- 



