470 



BELL SYSTEM TECHNICAL JOURNAL 



Figures 4 and 5 show two examples of these curves, from data 

 obtained while the sun was high in the sky. Actually there are two 

 curves in each of the figures; the appearance is that of a single curve, 

 repeated with a sidewise shift. I mention that this repetition is due 

 to the earth's magnetic field, but ask the reader to ignore for the 

 present the right-hand curve and fix his attention on the left-hand one. 

 Here he will see the E-branch, the gap, and the 7^-branch. The 



TIME IN MINUTES 

 10 9 8 



1200- 



1100- 

 •2 1000- 



UJ 



uu 900- 



5 



S 800- 

 2- 700- 

 g 600- 

 t 500- 



< 400- 



_i 



< 300- 

 I- 



5 200- 

 > 



100- 



0-* 





./ 





\* J 



^■i) 



J I I. 



2 3 456789 



FREQUENCY IN MEGACYCLES PER SECOND 



12 



Fig. 6 — Characteristic (/?',/) curves obtained with the multi-frequency apparatus; 

 sun high in sky, F\ crinkle apparent. (Carnegie Institution of Washington.) 



Upturns to right and left of the gap are striking on Fig. 5, insignificant 

 in Fig. 4. The F-branch is deformed by an enormous hump or crinkle. 

 This is supposed to correspond to a second gap, the upturns on right 

 and left being so pronounced as to give a perfect semblance of a peak; 

 indeed one sees in Fig. 5 how readily the gap between £ and F might 

 have been drawn as a peak. Curves of this sort are therefore taken 

 as evidence for three layers in the ionosphere, denoted by -E and F\ 

 and Fi. Sometimes there are signs of a fourth, lying between E and 

 F<i, and denoted by M or Ri. 



So great is the interest in curves like these, and so much do they 

 vary from time to time and from place to place, that lately there 

 have been more than a score of stations over the world engaged in 

 making them. At some of these the tracing of the curves is speeded 

 up and made incessant by a remarkable machine developed at the 



