SUN AND THE EARTH'S MAGNETIC FIELD — FLEMING 189 



Hiorter at Upsala confirmed, by a long series of observations, the 

 connection between auroral displays and disturbances in the normal 

 fluctuations of the needle. To explain these spectacular displays, 

 which appear as curtains, arches, bands, and rays, with many varia- 

 tions, extensive mathematical and experimental investigations have 

 been made, especially by our Norwegian colleagues. Birkeland, by 

 means of a cathode sphere in a vacuum chamber, demonstrated the 

 accumulation of electrons in the plane of the magnetic equator. 

 Since that time his distinguished successors, Stormer and Vegard, 

 have done much to advance the study of auroral phenomena. 

 Elaborate calculations of the paths of electrified corpuscles which 

 are entrapped between outermost lines of magnetic force of the 

 earth's field have been beautifully demonstrated in the laboratory 

 by Briiche. 



Minute particles in varying numbers are coming continually from 

 the sun. Once within the earth's magnetic field, these electrified 

 corpuscles are entrapped by the outermost lines of magnetic force. 

 When the particles pass through the atmosphere, they cause the 

 air to glow by their impact, and produce brilliant polar-light dis- 

 plays. From simultaneous photographs of aurora, taken at two 

 stations a known distance apart, it has been found that polar-light 

 beams generally do not come closer to the earth's surface than about 

 60 miles; some come no closer than 300 miles or more. Since the 

 height of polar lights is in no case less than 50 miles above the 

 ground, the conclusion is drawn that the magnetic variations and 

 disturbances also have their origin in electrical phenomena taking 

 place at least at greater heights in the atmosphere. This has been 

 confirmed in every respect and the study of the magnetic variations 

 is one of our main sources of information about the constitution 

 of, and the phenomena in, these outermost and inaccessible regions 

 of the atmosphere. 



Thus, inspection of data indicates an apparent interrelation of 

 the earth's field with the sun. The sun's magnetic field, even though 

 it is 100 times that of the earth, is far too weak to make its mag- 

 netic influence felt at the earth, 93,000,000 miles distant. It is much 

 more probable that solar influences on the earth's magnetism are 

 connected with enormous streams or clouds of particles, atoms, ions, 

 and electrons ejected from the active regions of the sun, which 

 travel through space and from time to time reach the earth after 

 1 or 2 days, and impinge upon its atmosphere, causing magnetic storms, 

 which often disturb electrical communications by cable, telegraph, 

 and radio. 



The regular daily magnetic variation apparently is the effect of 

 other radiations from the sun, which travel with the velocity of light 

 and are absorbed in the highest levels of the air, and which make 



