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HEI.L SYSTEM TECflXIC.IL JOURNAL 



(iimiial characteristic becomes e\i(Kiil. Tliis i> shown in I-'ig. 8, the 

 data lor which actually co\'er two \ears. 



Tile outstancling points to be observed in this figure are: 



1. The continuance of the high night-lime \aliies throughout the 

 \ear. 



2. The [lersislence of the high nigltt-time \alues for a longer period 

 in the winter than in the summer months. 



Fig. 8 — Monthly averages of fliurnal variation in signal field, Rwky F'oint, L. I. 



(2XS) to New Southgatc, Kngland, 57,(M)0 cycles— Ant. Current, 300 Amps— 



5480 Km. 1923-1924 



3. The da\ light \;dues show a coniparati\el\- small range of \aria- 

 tion. 



■I. The extreme range of \ariation shown between the minimum 

 of the sunset dip and the maximum of the high night-time values is 

 of the order of 1 to 100 in held strength. This is e(iui\alent to 1 to 

 lO.OOO in power ratio. 



It will be recalled tiial the cause of the seasonal changes upon the 

 earth's surface resides in the fact that the earth's axis is inclined .iiul 

 not perpendicular to the plane of its orbit about the sun. As I he 

 earth revolves about the sun, the sunlit hemisphere gradually extends 

 farther and farther northward in the si>ring months and by the summer 

 solstice reaches well l)eyond the north pole, as indicated in Fig. !). 

 As the earth continues to revolve about the sun, the sunlit hemisj^here 

 recedes southward until at the winter .solstice it fails considerably 

 short of the north pole and extends correspondingly beyond the 

 south pole. Since the transatlantic path lies fairly high in the north- 

 ern latitude, it is not surprising that the transmission conditions dis- 



