AUDIO FREQUENCY ATMOSPHERICS 



511 



These swishes were unusual in that they appeared in overlapping pairs. 

 Three minutes of record was obtained containing seven swish pairs. 

 A representative oscillogram, shown in Fig. 8, is a record of 2.4 seconds, 



O 1600 



0.8 1.0 



TIME IN SECONDS 



Fig. 9 — Frequency curve of the swish pair shown in Fig. 8. 



containing all that could be identified as a swish pair. The points 

 "^ " and "5" denote the visible starts of the first and second swishes 

 respectively. Filters used during the recording of this oscillogram 

 account for the absence of frequencies above 3000 c.p.s. and below 

 600 c.p.s. The frequency variation of this swish pair with time is 

 shown in the curve of Fig. 9. 



Eckersley ^^ has reported observations of descending whistling tones 

 following static crashes after a quiet period of a few seconds. During 

 the New Hampshire observations this phenomenon was observed fre- 

 quently. The swishes were observed to follow certain distinctive 

 static crashes. This type of disturbance consisted of low and inter- 



" T. L. Eckersley, "Radio Echoes and Magnetic Storms," Nature, 122, p. 768, 

 November, 1928. 



