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ANNUAL REPORT SMITHSONIAN INSTITUTION,, 1942 



seconds of 11'' 18™ Greenwich mean time, and ll*" 23™ was taken for 

 the time of disappearance. In this lapse of 5 minutes, the two patches 

 of light traversed a space of about 35,000 miles. The magnetic mo- 

 tion was in itself slight and of a character and magnitude frequently 

 recorded. Young expressed the prophetic opinion that these solar 

 disturbances are "propagated to our terrestrial magnetism with the 

 speed of light" and that the casual relationship is "only in the sense 

 that the pulling of a trigger 'causes' the flight of a rifle-ball." 



Thus, these classical observations could be properly interpreted 

 only after the recent discovery of radio fade-out and solar relations. 

 They are the first recorded instance of a large solar eruption and a 

 simultaneous large magnetic effect lasting less than an hour, pre- 

 sumably caused primarily by a transitory increase of ionization in 

 the ionosphere due to excessive ultraviolet light, followed after an 

 interval of about 18 hours by the outbreak of one of the nine most 

 violent magnetic storms observed from 1859 to 1941. 



FiGUEB 13. — Wide-range magnetogram, March 24-25, 1940, Potsdam-Niemegk, 

 Germany. (After G. Fanselau.) 



The magnetic storm of March 24, 1940, one of the greatest ever 

 recorded, was an event of unusual geophysical interest. This storm 

 was accompanied by auroral displays which, however, were not un- 

 precedented. The accompanying disruption of wire communication 

 by electric currents induced in the earth produced senseless jumbles 

 of letters in teletype equipment. These earth currents were of such 

 magnitude that electric power systems were severely affected — the 

 first time such effects have ever been reported. The reports of inter- 

 ference with power transmission, especially at stations in the eastern 

 United States and Canada, were at first doubted by electrical engi- 



