THE AURORA. 5 



resting on two parts of the horizon which are equally 

 distant from the direction towards which the needle 

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

 direction. From all this it appears, inconte stably, 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. Amongst 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 appeared 

 that the magnetic needle not only swayed responsively 

 to auroras observable in the immediate neighbourhood, 

 but to auroras in progress hundreds or even thousands 

 of miles away. Nay, as inquiry progressed, it was 

 discovered that the needles in our northern observa- 

 tories are swayed by influences associated even with 

 the occurrence of auroras around the southern polar 

 regions. 



In fact, not only have the difficulties pointed out 

 (very properly, it need hardly be remarked) by Sir 

 David Brewster been wholly removed ; but it has 

 been found that a much closer bond of sympathy 



