NATURAL PHILOSOPHY. 145 



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it is disengaged by the vegetation of tlie earth, or the continual evaporation 

 caused by the solar heat, philosophers have not yet determined) must be 

 expended and neutralized, or the electrical tension of the atmosphere, 

 instead of being contained within its actual limits, would go on constantly 

 increasing. In our latitudes, and under the equator, this discharge is effect- 

 ed by thunder-storms, rains, winds, and water- spouts ; but these do not 

 suffice ; they are purely accidental, and Nature is obliged to resort to a more 

 regular and constant method of operating the electrical neutralization. 

 He supposes that the positive electricity which abounds in the superior 

 regions of the atmosphere moves with perfect liberty in them, from their 

 extreme rarefaction, and that it takes advantage of this facility to go to the 

 nearest pole. Here it returns to the earth by a sort of continual, gentle 

 flow, (ccoulcmentt') which is greatly aided by the immense quantity of 

 frozen particles floating in the air. Here, instead of returning to the 

 ground in a single flash as we see it, through clouds of liquid particles, it 

 reverts to the ground by gradually passing from frozen particle to frozen 

 particle, exciting by partial discharges innumerable small aigrettes, which 

 singty are invisible, and yet whose total seen together presents the beauti- 

 ful appearance of the Aurora Borealis, and which having once reached 

 the earth give rise to different currents, which react in turn on the magnetic 

 needle. It may be asked why the phenomenon is concentrated around 

 the circumference of a circle, and is prolonged in parallel columns, and is 

 placed on the line of the magnetic axis of the globe, and why it is ani- 

 mated with an undulatory motion going from the West to the East, (for 

 all these phenomena accompany the Aurora Borealis ;) this question is 

 solved by a slight change introduced into the well-known experiment of 

 the " electrical egg," which consists in transmitting electricity from one to 

 the other pole in a receiver from which the air has been exhausted. M. de 

 la Hive magnetizes at will one of the two poles ; when neither is magnetized, 

 the common phenomenon takes place ; but as soon as he magnetizes either 

 of them, the light is distributed so as to form a ring, which is very much 

 like the form of the Aurora Borealis, and like it animated by a gyratory 

 motion. En resume, M. de la Hive holds that the Aurora Borealis is owing 

 to electrical discharges taking place in the polar regions, between the terres- 

 trial globe and the atmosphere, by means of icy particles suspended in it 

 there, while the charge takes place in the equatorial regions by the direct 

 or the indirect action of the sun. These electrical discharges taking place 

 constantly, but with varying intensity, according to the state of the atmos- 

 phere, the Aurora Borealis must be a daily phenomenon, although with 

 differing intenseness ; its visibility extends consequently to varying 

 distances, and depends also upon the transparency of the atmosphere 

 during the night. 



