6 LIGHT SCIENCE FOR LEISURE HOURS. 



exists between the magnetised 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 

 coloured 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 in^erest- 

 ing conclusions follow from this peculiarity. IFirst, 

 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- 

 stances which give interest and significance to the 

 strange discovery which is the subject of this paper. 



Could we only associate auroras with terrestrial mag- 

 netism, we should still have done much to enhance the 

 interest which the beautiful phenomenon is calculated 

 to excite. But when once this association has been 

 established, others of even greater interest are brought 

 into recognition. For terrestrial magnetism has been 

 clearly shown to be influenced directly by the action 

 of the sun. The needle in its daily vibration follows 



