THE EFFECT OF CLIMATE AND WEATHER 299 



If the earth should be deprived of sunlight all hfe would 

 soon perish, and the same thing would happen if the sunhght 

 were sufliciently intense. Thus there must be both lower 

 and upper Hmits of sunhght, but neither appears to be 

 reached naturally on any part of the earth's surface. The 

 dwellers in dense forests and in the Arctic region with its 

 long night seem at first thought to get as httle hght as 

 anyone, but as a matter of fact such people at certain 

 times or seasons get a great deal of Hght either directly 

 from the sky or by reflection from the snow. The people who 

 really approach the lower hmit appear to be the poorest 

 workers in the factories of our smokiest cities. In some 

 places such people may be slowly dying for lack of sunhght, 

 even if other conditions are not intolerable. As to the upper 

 limit, Woodruff, in an interesting book on "Tropical Light," 

 maintained that the hght within the tropics approaches the 

 upper hmit for the white man, but experiments on both 

 men and monkeys indicate that much of the ill effect which 

 he ascribed to hght is really due to heat. Yet the intensity 

 of the hght may reduce human efficiency in the great 

 tropical deserts. Long experience has convinced the Arabs 

 that they need heavy, opaque clothing and headgear 

 to keep out the sunhght. How far this is for protection 

 against heat and how far against sunlight is not clear, but 

 the trouble which such people experience from the desert 

 glare is enough to show that the light is too strong. 



The limits of atmospheric movement include almost com- 

 plete quiescence at one extreme and intolerable gales at 

 the other. If the air should become absolutely quiet, the 

 exhalations from plants and animals, and from man and his 

 works, would soon contaminate it to a degree that can 

 scarcely be appreciated. Evaporation would saturate the 

 the lower atmosphere with vapor, thus intensifying the ill 

 effects of the gases and odors. Life would become intolerable. 

 An approach to such conditions is found in a few sheltered 

 and undrained valleys where volcanic gases temporarily 

 accumulate, and in the streets and tunnels of great cities 

 where the fumes from factories, automobiles and other 

 sources poison the air. On the other hand, if the wind were to 

 blow constantly with hurricane force, the larger forms of life 



