Yet another singular fact, almost mystical in its suggestions, may be mentioned. It seems that the dance of the auroral lights occurs most frequently during the absence of the moon from the hemisphere in which they appear, and that they flee, in greater part, to the opposite hemisphere when the moon’s revolution in an orbit considerably inclined to the earth’s equator brings her into that where they have been performing. Arrhenius himself discovered this curious relation of auroral frequency to the position of the moon north or south of the equator, and he explains it in this way. The moon, like the earth, is exposed to the influx of the ions from the sun; but having no atmosphere, or almost none, to interfere with them, they descend directly upon her surface and charge her with an electric negative potential to a very high degree. In consequence of this she affects the electric state of the upper parts of the earth’s atmosphere where they lie most directly beneath her, and thus prevents, to a large extent, the negative discharges to which the appearance of the Aurora is due. And so “the extravagant and erring spirit” of the Aurora avoids the moon as Hamlet’s ghost fled at the voice of the cock announcing the awakening of the god of day. There are even other apparent confirmations of the hypothesis, but we need not go into them. We shall, however, find one more application of it in the next chapter, for it appears to be a kind of cure-all for astronomical troubles; at any rate it offers a conceivable solution of the question, How does the sun manage to transmit its electric influence to the earth? And this solution is so grandiose in conception, and so novel in the mental pictures that it offers, that its acceptance would not in the least detract from the impression that the Aurora makes upon the imagination. X Strange Adventures of Comets