ON SOLAR RADIATION. 



151 



/ 



A projection of the ratios gives a curve closely resem- 

 bling the curve No. 1, diagram B (p. 132), and therefore 

 strongly supporting the view that the calorific intensity of 

 the sun^s rays varies in a period corresponding with the 

 solar-spot period. 



If instead of the difference between the mean tempera- 

 tures of the air and of evaporation we employ the differ- 

 ence between the mean temperatures of the air and of the 

 dew-point we obtain the following ratios : — 



1859 

 i86o 

 1861 



^•33 

 2-57 



2*17 



1862 

 1863 

 1864 



1-66 

 1-65 



1-72 



It will be seen that the curve representing these ratios 

 is identical in form with that representing the last series 

 of ratios, as indeed might have been expected. 



Proceeding, now, to apply the same method to the treat- 

 ment of the mean monthly values of solar radiation we 

 have the following Table : — 





Mean monthly 

 solar radiation. 



Mean 

 temperature 



of air less mean 

 temperature 



of evaporation. 



Ratio. 



January 







9'i6 



io-o8 

 13-23 

 12-90 

 12-93 

 13-81 



i4'03 



13 71 



9-66 



8-00 



4-50 







i'3i 



175 

 2*36 

 3*oo 

 378 

 3-43 

 4-15 

 373 

 2-81 

 2-05 

 I -41 

 1-^5 



4"20 



5-23 

 4-27 

 4-41 



3-41 

 376 

 3'32 

 376 

 4-88 



471 

 5-67 

 3"9i 



February 



March 



April 



May 



June 



July 



August 



September 



October 



November 



December 





Before the true import of the numbers in the last column 

 can be clearly understood, it will be necessary to apply 

 corrections for the changes of meridian altitude of the sun 

 in the different months of the year ; and employing for this 



