As the phosphorescence of the sea is owing to living creatures, it must naturally show itself in its greatest brilliancy when the ocean is at rest; for during the daytime we find the surface of the waters most peopled with various animals when only a slight zephyr glides over the sea. In stormy weather, the fragile or gelatinous world of the lower marine creatures generally seek a greater depth, until the elementary strife has ceased, when it again loves to sport in the warmer or more cheerful superficial waters. In the tropical zone, Humboldt saw the sea most brilliantly luminous before a storm, when the air was sultry and the sky covered with clouds. In the North Sea we observe the phenomenon most commonly during fine, tranquil autumnal nights; but it may be seen at every season of the year, even when the cold is most intense. Its appearance is, however, extremely capricious; for, under seemingly unaltered circumstances, the sea may one night be very luminous and the next quite dark. Often months, even years, pass by without witnessing it in full perfection. Does this result from a peculiar state of the atmosphere, or do the little animals love to migrate from one part of the coast to another? It is remarkable that the ancients should have taken so little notice of oceanic phosphorescence. The _Periplus_ of Hanno contains, perhaps, the only passage in which the phenomenon is described. To the south of Cerne the Carthaginian navigator saw the sea burn, as it were, with streams of fire. Pliny, in whom the miracle (miraculum, as he calls it) of the date-shell excited so lively an admiration, and who must often have seen the sea gleam with phosphoric light, as the passage proves where he mentions in a few dry words the luminous gurnard (_lucerna_) stretching out a fiery tongue, has no exclamation of delight for one of the most beautiful sights of nature. Homer also, who has given us so many charming descriptions of the sea in its ever-changing aspects, and who so often leads us with long-suffering Ulysses through the nocturnal floods, never once makes them blaze or sparkle in his immortal hexameters. Even modern poets mention the phenomenon but rarely. Camoens himself, whom Humboldt, on account of his beautiful oceanic descriptions, calls, above all others, the “poet of the sea,” forgets to sing it in his _Lusiad_. Byron in his _Corsair_ has a few lines on the subject: “Flash’d the dipt oars, and, sparkling with the stroke, Around the waves phosphoric brightness broke;” but contents himself, as we see, with coldly mentioning a phenomenon so worthy of all a poet’s enthusiasm. In Coleridge’s wondrous ballad of _The Ancient Mariner_ we find a warmer description: “Beyond the shadow of the ship I watch’d the water-snakes: They moved in tracks of shining white, And, when they rear’d, the elfin light Fell off in hoary flakes.