THE AURORA. 11 



precisely the point to which a magnetized needle sus- 

 pended by its centre of gravity directs itself. 



It has, moreover, been shown that the concentric 

 circular segments, almost similar in form to the rain- 

 bow, which are usually seen previous to the appearance 

 of the luminous streamers, have their two extremities 

 resting on two parts of the horizon which are equally 

 distant from the direction toward which the needle 

 turns ; and the summit of each arc lies exactly in that 

 direction. From all this it appears, incontestable/, that 

 there is an intimate connection between the causes of 

 auroras and those of terrestrial magnetism" 



This strange hypothesis was, at first, much opposed 

 by scientific men. Among others the late Sir David 

 Brewster pointed out a variety of objections, some of 

 which appeared at first sight of great force. Thus, he 

 remarked that magnetic disturbances of the most 

 remarkable character have often been observed when 

 no aurora has been visible ; and he noticed certain 

 peculiarities in the auroras observed near the polar 

 regions, which did not seem to accord with Arago's 

 view. 



But gradually it was found that physicists had mis- 

 taken the character of the auroral display. It ap- 

 peared that the magnetic needle not only swayed 

 responsively to auroras observable in the immediate 

 neighborhood, but to auroras in progress hundreds or 

 even thousands of miles away. Nay, as inquiry pro- 



