112 



RAnr\TI<)\ ItlOLOGY 



3-10 which ti;ave Eh in terms of the zenith nnp}o of the sun. From this, 

 I'Jh was calculated throuj^ihout the day for various latitudes and seasons. 

 The results are plotted in Fijj;. 3-12 for (he twenty-second day of March, 

 June, September, and December for north latitudes 0°, 20°, 40°, ()0°, and 

 80°. The curves for March and September are the same at all latitudes 

 becaus(» the zenith ;inu;lo of the sini is the same at these epochs; at the 

 — I 1 1 1 1 — 



N* 



3 4 1 2 3 4 



M M 



Fig. 3-11. Values of Eh for wave lengths less than 3130 A. Group I. for most smoky 

 loealities; Group III. for least smoky localities. {Ives and Gill. 1937.) 



equator the curves for .June and December are the same for the .same 

 reason. For December at 60° north latitude and for March, September, 

 and December at 80°, the sun does not rise above 10° above the horizon, 

 and Kh i« zero throughout. At 80° the value of Eh in June remains above 

 zero all night, being 3 at midnight because the midnight sun is 14° above 

 the horizon. In the curves of Fig. 3-12, no seasonal adjustments have 

 been made for the fact that the sun is about 3 per cent nearer the earth 

 on December 22 than it is on June 22. Since the values of Eh of Fig. 

 3-12 are based on the data of Fig. 3-10 obtained on clear days in the 

 United States, they may be expected to be correct for localities outside 

 the United States only if the localities have the same ozone and the same 



