12 LIGHT SCIENCE FOR LEISURE HOURS. 



grossed, it was discovered that the needles in our 

 northern observatories are swayed by influences asso- 

 ciated 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 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 synchro- 

 nous with the waving movements of the mysterious 

 streamers. An aurora may be in progress in the north, 

 of Europe, or even in Asia or America, and as the 

 colored banners wave to and fro, the tiny needle, 

 watched by patient observers at Greenwich or Paris, 

 will respond to every phase of the display. 



And I may notice in passing that two very inter- 

 esting conclusions follow from this peculiarity : First, 

 every magnetic needle over the whole earth must be 

 simultaneously disturbed; and, secondly, the auroral 

 streamers which wave across the skies of one country, 

 must move synchronously with those which are visible 

 in the skies of another country, even though thousands 

 of miles may separate the two regions. 



But I must pass on to consider further the circum- 



