DYNAMIC METEOROLOGV. 



405 



According to Pouillet (Paris, Coinptes Reiuliis, 1838, tome vir, pp. 

 24-65), a surface of 1 square centimeter exposed perpendicularly to the 

 sun's rays at the outer limit of the atmosphere receives 0.00L7G33 cal- 

 orie per minute (this calorie being the amount of heat required to raise 

 I kilogram of water 1<^ C). The same plate at the earth's surface 

 and with the sun in the zenith would, owing to the absorption by the 

 atmosphere, receive only 0.76 of the above, or 0.0013401 calorie per 

 minute. 



(This is the result of observation on six very clear days in 1837-'38, 

 but observations by others have generally shown a higher value for the 

 amount of heat originally incident on the outer surface of the atmos- 

 phere.) 



Adopting 25 instead of 24 per cent, as an approximation to the ab- 

 sorption by our atmosphere in the clearest weather, when the sun is in 

 the zenith, it has been shown that of the total heat received by the 

 illuminated half of the earth and atmosphere, about 40 per cent, is 

 absorbed by the air, and about 60 per cent, reaches the surface of the 

 earth; this latter is the average percentage for the whole illuminated 

 disk whose border receives at the earth's surface no transmitted heat, 

 but whose center receives 75 per cent, of that incident on the outer at- 

 mosphere. 



Therefore, in order to know the distribution over the earth's surface 

 of the heat that penetrates the atmosphere, we must subtract this large 

 absorption from the figures in Tables i, ii, and iii (omitted here for 

 brevity, but easily found in Meech, Angot, Radau, Heuuessy, and other 

 authorities), and thus obtain the results given in Tables iv, V, and vi, 

 as follows : 



Table IV. — Relative solar heat, after absorption hy the atmosphere, as received at the 

 earth's surface in one minute for varying altitudes of the sun. 



