NORTHERN LIGHTS. 805 



through our globe, here appearing, there receding, but forever 

 seeking to attain its equilibrium. The instrument by which these 

 occurrences are observed is the most simple conceivable the 

 magnetic needle. It is known that the direction and the inclina- 

 tion of the needle point out the magnetic location of a place. 

 From its movement the degree of magnetic attraction of any 

 point may be accurately determined. If sudden deviations and 

 fluctuations of the needle occur, this evidently is an indication 

 that the magnetic condition of the earth has been disturbed. If 

 such variations always occur simultaneously with the appearance 

 of northern lights, this is to be regarded as proof that an inti- 

 mate relation exists between these phenomena and terrestrial 

 magnetism. Strong northern lights, in fact, exert so great an 

 influence on the magnetic condition of the earth, that the appear- 

 ance of the phenomenon in some northern latitude may be in- 

 ferred from the sudden oscillations of the needle in places where 

 the lights are not visible. But the most striking connection be- 

 tween terrestrial magnetism and northern lights is shown by the 

 position of the light-crown in the heavens. The center of this is 

 always to be found at that point where the dipping-needle, if pro- 

 longed, would meet the aurora. The rays emanating from the arc 

 have the direction of the earth's magnetic power ; they are there- 

 fore parallel, and only apparently converge to a point. The crown 

 of light has in truth no fixed place in the heavens, but like the 

 rainbow its position depends on the point from which it is ob- 

 served, and thus moves with the observer. But the dipping-needle 

 in every place points to the center of the crown. 



It may hence be asserted that the northern lights hold an inti- 

 mate relation to the changes of terrestrial magnetism as indi- 

 cated by the oscillation of the needle, and that both phenomena 

 must have one and the same cause. The explanation of this 

 cause has been sought in various ways, but an interpretation 

 which would be universally accepted has thus far not been ad- 

 vanced. One of the first attempts to solve the problem was made 

 by the physicist De la Rive, of Geneva, in 1862. It was based on 

 an experiment devised by him, in which he attempted an imita- 

 tion of these phenomena on a small scale. He held that vapors 

 charged with positive electricity rise into the higher regions of 

 the atmosphere, while the earth remains charged with the nega- 

 tive fluid. When the vapors are driven by the trade-winds to the 

 poles, as soon as the tension is sufficient to overcome the non-con- 

 ducting property of the air, which like an insulator lies between 

 the earth and these vapors, the positive and the negative electricity 

 come together. This process is accompanied by the appearance 

 of light. The earth and the upper layer of the atmosphere must 

 hence be regarded as an electrical condenser, with the lower layers 



