104 STRANGE HYPOTHESIS. 



scene of the display becomes covered with scattered streaks and 

 patches of ashen-gray light, which hang like clouds over the north- 

 em heavens. Then these in turn disappear, and nothing remains 

 of the brilliant spectacle but a dark smoke-like segment on the 

 horizon. 



" Hitherto the nature of the aurora has been a mystery to men 

 of science. Let it be premised, then, that physicists had long 

 since recognized in the aurora a phenomenon of more than local, 

 of more even than terrestrial significance. They had learned to 

 associate it with relations which affect the whole planetary 

 scheme. 



" Arago was engaged in watching from day to day, and from year 

 to year, the vibrations of the magnetic needle in the Paris Observa- 

 tory. In Jan., 1819, he published a statement to the effect that the 

 sudden changes of the magnetic needle are often associated with 

 the occurrence of an aurora." The statements are then given in 

 his own words, and from them the following deduction is made : 

 ^^From all this it appears incontestably that there is an intimate 

 connection between the causes of auroras and those of terrestrial 

 magnetism r 



This strange hypothesis, was, at first, much opposed by scientific 

 men, but gradually it was found that physicists had mistaken the 

 character of the auroral display. It appeared that the magnetic 

 needle not only swayed responsively to auroras observable in the im- 

 mediate neighborhood, but to auroras in progress hundreds, or even 

 thousands of miles away. It has been found that a much closer 

 bond of sympathy exists between the magnetized needle and the 

 auroral streamers than even Arago had supposed. It is not merely 

 the case that while an auroral display is in progress, the needle is 

 subject to unusual disturbance, but the movements of the needle 

 are actually synchronous with the waving movements of the mys- 

 terious streamers. 



" I may notice in passing that two very interesting conclusions 

 follow from this peculiarity : First, every magnetic needle over the 

 whole earth must be simultaneously disturbed ; and, secondly, the 



