Decembeb 17, 1909] 



SCIENCE 



861 



distances of upwards of two millions of 

 miles or possibly farther than that, but 

 doubtless they keep on outwardly, and in- 

 visibly, to relatively enormous distances. 

 It is not unreasonable as a hypothesis to 

 imagine that they may extend at times as 

 far as the orbit of the earth and may, if 

 the direction is the proper one, reach our 

 outer air. 



Further, if they consist of electric ions 

 or particles conveying electric charges, an 

 aurora may result. Dr. Hale, of Mt. Wil- 

 son Observatory, has indeed recently shown 

 by the spectroscope that great solar storms 

 are in fact attended by the motion of elec- 

 tric ions at enormous velocities. The phe- 

 nomena of auroras present peculiar difficul- 

 ties in their study, since, as in the case of 

 the rainbow, no two observers at a distance 

 from each other see the same or identical 

 appearances. Hence attempts to determine 

 the height by triangulation at which au- 

 roras exist give most contradictory results, 

 for it is impossible to fix upon any con- 

 densation or streamer which may not be 

 displaced or absent to another observer 

 some distance away. This is understood 

 when we bear in mind that the luminous 

 appearances are not located in one plane, 

 but are distributed in space; condensations 

 of light being the result of superposition in 

 the line of observation. 



I have come to the opinion that the 

 auroral streamers often extend in a gen- 

 eral direction outwardly from the earth, 

 sometimes to very great distances rela- 

 tively to the known extent of our atmos- 

 phere. The effects observed appear unac- 

 countable upon any other supposition, 

 while they are consistent with the idea of 

 outwardly directed streams of great ex- 

 tent. In April, 1883, there occurred an 

 aurora which was at its maximum a little 

 after midnight. It was the most magnifi- 

 cent display of the kind, which, in spite of 



a continual vigilance on my part, it has 

 l^een my fortune to witness. It was upon 

 such a scale that, so to speak, the mechan- 

 ism of the streamers stood revealed. At 

 that time I could not avoid the conclusion 

 that the auroral streamers must have ex- 

 tended outwardly several thousand miles. 

 There is no space here to present the argu- 

 ment involved. Perhaps the most signifi- 

 cant fact is that precisely the same gen- 

 eral appearances were noted in Chicago as 

 in the east, and that they occurred simul- 

 taneously. The interesting question arises, 

 does the earth temporarily acquire stream- 

 ers similar in nature to the solar coronal 

 streamers 1 The answer is as yet unknown. 

 At the time of the great display men- 

 tioned there was a sunspot near the center 

 of the sun's disc of about .50,000 miles in 

 diameter. During that disturbance long 

 telegraphic lines could not be operated, 

 owing to arcing at the keys which pre- 

 vented interruption of the circuits. Ap- 

 parently in subtle sympathy with its 

 master orb, the sun, the earth's electric 

 and magnetic equilibrium was for a time 

 profoundly disturbed. 



While it is by no means certain that 

 auroras and magnetic storms are always 

 dependent on solar outbursts, it is now 

 generally recognized that the observed co- 

 incidences are too frequent to be the result 

 of chance. It is perhaps safe to assume 

 that although solar storms and sunspots 

 can occur without provoking auroras or 

 magnetic storms here, it may be doubted 

 if these latter occur on any great scale un- 

 less solar activity is coincident therewith. 

 And it seemingly is true that only when 

 the projected electrified matter actually 

 reaches the earth or comes near enough to 

 inductively affect its electrical equilibrium 

 are the terrestrial phenomena produced 

 thereby. 



It has even been suspected that a greater 



