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HERE is a curious myth which gives to Castor and Pollux, twin sons of Zeus, a divine control over the phosphorescence of air and ocean. Being present by invitation at the marriage of two youths of Amyclæ with the daughters of Leucippus, they became enamored of the brides and with the doubtful courtesy of the period attempted to carry them off. In the ensuing struggle Castor was slain; but Pollux, with a boundless and heroic love that bridged the "abyss 'twixt life and death," besought their father Zeus to restore him, proposing that to meet the ends of justice they should each live only on alternate days. This he granted, and, "kindling stars upon their brows, set them for ever with the immortals."

A religious idea was therefore involved in the superstition of the ancient mariner that the pale phosphoric light, or "St. Elmo's fire," which occasionally appears upon the masts of ships, in an electrical condition of the air, denoted the presence of these divinities as they rode upon the storm-clouds through the heavens. This indicates a recognition of the phenomena of phosphorescence in a remote antiquity; but, in advancing from the philosophy of myths and symbols to an era of empirical knowledge, there was necessarily a period of confusion, when old fancies were replaced by new facts which had not accommodated themselves to the novelty of the position. Even when, through the onward roll of centuries, the wisdom of the ancients had shrunken into grotesque fables, a long period intervened which produced no marked scientific results.

Throughout the seventeenth century inquiry was directed to the phenomena of solar light and the light of incandescent bodies; but, while phosphorescence was everywhere observed, no explanation on scientific principles was attempted, until in 1675 Nicolas Lémery, in a paper on the preparation of solar phosphorus, stated that the light produced was the result of rapid molecular motion; thus accepting the doctrine foreshadowed by Huygens and Euler, in opposition to the emission or corpuscular theory of Newton. These prophetic utterances, however, of the present undulatory theory of light were not recognized; it was reserved for later experiment to demonstrate the truth of this intuitive perception.

The "persistence of force" and the "indestructibility of matter" must first be proved, before it could be shown that the phenomena of phosphorescence are due to the same causes as the light evolved by electrical discharge, chemical combination, or mechanical movement. If, as Dr. Young has shown, light be motion or vibration of a luminiferous ether which fills space and permeates all bodies, the conditions