32 



Mr. E. M. Deeley 



the 



Table II., after Zenke, gives the intensity of the insolation 

 at the earth's surface for different solar altitudes. Here A is 

 the altitude of the sun, B the relative length of the path of 

 the rays through the atmosphere, C the intensity of insolation 

 on a surface perpendicular to the rays, D the intensity [of 

 insolation on a horizontal surface, and E the insolation inter- 

 cepted by the atmosphere. 



Table II. 



A. 



B. 



C. 



I). 



E. 







44-7 



o-oo 



000 



100 



5 



108 



015 



o-oi 



0-85 



10 



5-7 



0-31 



0-05 



0-69 



20 



2-9 



0-51 



017 



049 



30 



2-0 



0-62 



031 



0-38 



40 



1-56 



068 



0-44 



0-32 



50 



1-31 



072 



0-55 



0-28 



60 



115 



075 



0-65 



025 



70 



1-06 



0-76 



0-72 



024 



80 



102 



0-77 



076 



0-23 



90 



1-00 



0-78 



0-78 



022 



If these figures be correct, 78 per cent, of the sun's heat 

 reaches the ground on a fine day when the sun is vertical ; 

 but when the altitude of the sun is only 10°, then only 

 31 per cent, reaches a surface perpendicular to the sun's 

 rays, the rest being intercepted by the atmosphere. 



Column E, Table II., shows the percentage of insolation 

 arrested by the atmosphere for varying sun altitudes calcu- 

 lated from the figures in column C. If, as these figures 

 would indicate is the case, the proportion of the sun's heat 

 arrested by the atmosphere in high latitudes is much greater 

 than is the case in low latitudes, several important conse- 

 quences follow. 1st. In high latitudes, although a con- 

 siderable proportion of the sun's rays striking the snow 

 or ice-covered surface is reflected, these reflected rays 

 will be short period waves of little heating power; for 

 the atmosphere has absorbed the long ones. 2nd. The 

 greater proportion of the sun's heat will go directly to 



