The atmosphere is constantly charged with positive electricity,--electricity furnished by the vapors that rise from the sea, especially in tropical regions,--and, on the other hand, the earth is negatively electrized. The recomposition or neutralization of the two opposite electricities of the atmosphere and of the terrestrial globe is brought about by means of the moisture with which the lower strata of the air are more or less charged. But it is especially in the polar regions, where the eternal ice that reigns there constantly condenses the aqueous vapors under the form of haze, that this recomposition must be brought about; the more so, as the positive vapors are carried thither and accumulated by the tropical current, which, setting out from the equatorial regions, where it occupies the most elevated regions of the atmosphere, descends as it advances towards the higher latitudes, until it comes in contact with the earth in the neighborhood of the poles. It is there, then, chiefly, that the equilibrium between the positive electricity of the vapors and the negative electricity of the earth must be accomplished by means of a discharge, which, when of sufficient intensity, will be accompanied with light, if, as is almost always the case near the poles, and sometimes in the higher parts of the atmosphere, it take place among those extremely small icy particles which constitute the hazes and the very elevated clouds. There can be no doubt that the occurrence of the phenomenon is materially dependent on the presence in the atmosphere of these particles of ice, forming a kind of thin haze, which, becoming luminous by the transmission of electricity, must appear simply as an illuminated surface of greater or less extent, and more or less cut up. The phenomenon actually takes place in this manner in the parts of the atmosphere that are the most distant from the earth. We perceive what are termed auroral plates of a purple or reddish-violet color, more or less extended, according as this species of veil, formed by icy particles, extends to a greater or less distance from the poles. The tenuity of this veil is such that it admits of our seeing the stars through the auroral plates. Of its existence, independently of indirect proofs, we have a direct demonstration in the observation of MM. Bixio and Baral, who, being raised in a balloon to a great height, found themselves, on a sudden, although the sky was entirely serene and the atmosphere cloudless, in the midst of a perfectly transparent veil, formed by a multitude of little icy needles, so fine that they were scarcely visible.