THE NORTHERN LIGHTS 85 



the electromagnet pick up iron now ? Can it pick up any- 

 thing except iron and steel ? Disconnect the dry cell. Is the 

 nail a magnet now ? Note : Do not leave dry cell attached to 

 magnet for more than a few seconds at a time, or the dry cell 

 will be spoiled. 



c. Approach the electromagnet to the suspended magnet. 

 Has it two poles ? Change the connection of the dry cell and 

 test the electromagnet by the suspended magnet. What 

 has happened? Electricity is reversible, and magnetism 

 likewise. 



63. THE NORTHERN LIGHTS 



At night in the far north the northern sky is often illumi- 

 nated with beautiful fluttering streamers of colored light which 

 now grow brighter, now dimmer; often changing in color, 

 they are ever glorious. At the same time that these wonder- 

 ful displays take place, the magnetic needles quiver and jump, 

 showing that there is some connection between the Northern 

 Lights and the earth's magnetism. A theory which is rapidly 

 gaining in favor with scientists is that the magnetism of the 

 earth and the Northern Lights both owe their origin to the 

 electrical energy which the earth is receiving from the sun. 

 Since sun spots influence the magnetic needle, the relation 

 seems to be reasonable. Electrical discharges through rare- 

 fied gases produce, in a small way, the same color effects as are 

 manifested in the Northern Lights. 



References : 



1. 1002:139. The Aurora. 



2. 1103: 175-176. The Aurora and its Cause. 



3. 1304:419. The Aurora Borealis and Australis. 



a. 1102 : 270-271. The Aurora Borealis. 



b. 1303:18-19. The Aurora. 



