4S6 



BELL SYSTEM TECHNICAL JOURNAL 



that this orciirs during the winter at aliout sunrise, at the ecjuinox 

 about an hour later, and during the summer some two hours later. 



It will be observed that the two sets of curves, one for sunset and 

 the other for sunrise, intersect at approximately the same latitude, 

 the sunset curves southeast and the sunrise curves southwest of 



Kig. 21 — I'osition of sunset lines at sunset dip and sunrise lines at sunrise dip in 

 noise level in England for various seasons 



Kngland. If it is assumed that the effect of the shadow wall upon the 

 transmission of static is similar to that upon signal transmission across 

 the Atlantic, namely, the high night-lime values commence when 

 the shadow wall is approximately half-wa\- between the terminals, 

 the crossing of the lines upon the chart may be taken as having sig- 

 nificance in roughh' determining the limits of the tropical area from 

 which the major static originates. The crossing of the sunset lines 

 indicates that the eastern limit of the area which contributes most 

 of the static to Kngland is equatorial East Africa. Tlie crossing 

 of the sunrise lines indicates that the corresponding western limit 

 is somewhere in the South Atlantic, between Africa and South America. 

 In other words, from these data the indications are that there is a 

 more or less distinct center of gravity of static, which extend along the 

 tropical belt, and that most of the long-wave static which affects 

 reception in Kngland comes from the equatorial region to the south 

 of England, namely, ctiuatorial Africa. This is exclusive of the high 

 afternf)on static prevailing during the summer months. 



