ON THE CALCULATION OF SUN-HEAT COEFFICIENTS. 



69 



Sun-heat Forrnulce. 

 Heat received per sq. unit, in unit of time is represented by 



Ap u cos z. 

 A = the solar constant ; 

 p = atmospheric absorption constant ; 

 u = */2rh + 7t 2 + r 2 cos 2 z —r cos z ; 

 z = sun's zenith distance ; 

 h = height of atmosphere ; 

 r = radius of earth ; 

 p = 0-76 (Pouillet). 



(I.) To calculate u. — 



u = r 



2h h* 

 cos 2 z + — + - 2 



— r cos 2. 



If h = 50 miles, - = 57:. 

 ' r 80 



Therefore, 



u 



= 80 a / cos 2 z + jq — 80 cos z ; 

 u = 80 Vcos 2 2 + 0-025000 - 80 cos z. (4) 



