on the Northern Hemisphere at Summer Solstice. 357 



the curve rises rather smoothly and slowly ; at about 55° N. 

 lat. the curve begins to get steeper with the concavity 

 upwards, and at the highest latitudes again it turns more flat 

 with a downward concavity. The situation of turning-point 



7) - W 



for which -^ --., = seems from the figure to be near 



p=70°K lat. 



Fig. 1. — Distribution of the violet and ultraviolet light (actinic on an 

 explosive mixture of hydrogen and chlorine) at summer solstice at 

 different Latitudes. 



igln-miits 



110 000 



100 000 - 



90 000 



B0 01 i 



70 000 



€0(00 





40 000 



I )■ 





]n 20 40 50 



diffused daylight. 



direct sunlight. 



quantity of light. 



- 10000 



30 000 



2 i 



80 9o e N. lat. 



