[A] And even so late as 1872, the brilliant aurora which was seen as far south as Alexandria, was believed by the intelligent Parisians to forebode terrible wars, and the speedy overthrow of the hated Germans, who had so lately trampled their capital and their pride. And in earlier days the northern light had been deemed the harbinger of war, famine or pestilence. Humboldt, and others since, have supposed the aurora to be light emitted by the earth itself; but to-day its electric character is proven beyond a doubt. Electric discharges passed through a tube containing greatly rarefied dry air produce the same effect on a small scale; and every aurora produces a powerful disturbance of magnetic instruments. In most cases, they are attended by a hissing, crackling noise: so the Siberians are wont to say that “the raging host is passing.” We find occasional references to the aurora among ancient writers, but little attempt to explain it. So we have even few myths, it not being common enough in warmer climes to hold a place in popular tales. But in Iceland, and more northern regions, it is of constant and brilliant occurrence, merely because it requires dry air, and the coldest air is the driest. So among Scandinavian races appears the myth embodied by Longfellow in the “Saga of King Olaf.” The war god, Thor, speaks: “The light thou beholdest Stream through the heavens In flashes of crimson, Is but my red beard, Blown by the night wind, Affrighting the nations.” And Scott has told us of the belief in Scotland and the northern isles, of spirits abroad in the upper air: “The monk gazed long on the lovely moon, Then into the night he looked forth: And red and bright, the streamers light, Were dancing in the glowing north. So had he seen, in fair Castile, The youth in glittering squadrons start, Sudden the flying jennet wheel, And hurl the unexpected dart. He knew by the streams that shot so bright, That spirits were riding the Northern light.” The light emitted by the aurora varies much in intensity. Ordinarily it is not greater than that of the moon in her first quarter; but a few instances are recorded where it was powerful enough to make itself perceptible by day; and on one occasion it was strong enough at night to cast a shadow in the midst of a Newfoundland fog. As the phenomenon has been carefully studied only within a century, it is not safe to affirm with certainty what records of the past three hundred years have induced many to believe; that it is of special frequency at periods of one hundred and fifty years. This can only apply to the temperate zones; for in the polar world it is to be seen on almost every clear still night.