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BELL SYSTEM TECHNICAL JOURNAL 



the order 35 db. Tlie effect upon transmission lasted several days, 

 the recovery appearing to have been slower than the initial effect. 



A high degree of coincidence has been found to exist between these 

 adverse effects in short-wave transmission on the one hand, and on 

 the other hand the appearance of earth currents and abnormalities in 

 the earth's magnetic field. This is a subject which cannot be ade- 

 quately treated in the present paper and it is hoped that a report upon 

 it can be made to the Institute during the forthcoming winter. As is 

 explained below radio transmission is believed to be largely dependent 



Jul; I92J 



Fig. 8 



— Magnetic storm effects, showing drop in field strength and appearance ol 

 earth potentials. 



on the state of ionization of the earth's atmosphere. Earth potentials 

 are probably also affected by variation in this ionic state. Therefore, 

 we have in such a recorder a useful check on the transmitting medium 

 when transmission difficulties are encountered. Such earth potential 

 observations may prove to be useful in exploring these conditions 

 more generally throughout the world. 



In Fig. 8 each point of the radio data was obtained by averaging 

 the field strength of the carrier throughout a 24-hour period. Fig. 9, 

 on the other hand, presents in a more detailed manner the way in 

 which the field strength varied throughout each of seven days, be- 

 tween June 24 and July 1, 1930, on transmission from England to the 



