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BELL SYSTEM TECHNICAL JOURNAL 



field strength tended to be higher than during the years of sunspot 

 minimum. The same appHes to solar limb-prominences, magnetic 

 activity, and ultra-violet radiation. f The irregularities in the radio 

 telephone field strength curves are more nearly duplicated in the curves 



2 



I 

 0.6 



0.2 



0.1 



5 10 15 20 25 30 35 40 



SIGNAL FIELD STRENGTH IN DECIBELS ABOVE ONE MICROVOLT PER METER 



Fig. 1 — Cumulative distribution of hourly observations of the field strength of 

 WNL — 60 kr. at Cupar, Scotland, in 1933, corrected to 375 amperes. ( 1 699 observa- 

 tions for all-daylight path, 1146 observations for all-night-time path.) 



t The measure of ultra-violet radiation is the ratio of intensity of ultra-violet 

 (X = 0.32jLi) to green (\ = 0.50m). Ratio for June 1924 = 1. 



