Table 99. 



RELATIVE AMOUNTS OF SOLAR RADIATION RECEIVED ON A 

 HORIZONTAL SURFACE DURING THE YEAR AT DIFFERENT LATITUDES. 



Table 1 GO. 



AIR MASS, M, CORRESPONDING TO DIFFERENT ZENITH DISTANCES 



OF THE SUN. 



Table 101 



RELATIVE ILLUMINATION INTENSITIES. 



Source of illumination. 



Zenithal sun 



Sky at sunset 



Sky at end of ci\ii twilight. 



Zenithal full moon 



Quarter moon 



Starlight 



Foot-candles. 



9600. o 

 33 00 

 0.40 

 0.02 

 0.002 

 0.00008 



465000. c 



1650. o 



20. o 



I.O 

 O. I 



0.004 



Smithsonian Tables. 



226 



