Any person who has sailed on the Atlantic must have noticed the luminous appearance of the water of the ocean, especially at night and in tempestuous weather. This beautiful phenomenon is witnessed to a greater extent in some parts of the ocean than in others, and in different sections it presents different appearances. In one place it seems uniformly luminous, shining feebly with a pale and sickly light; in another it exhibits bright flashes; again, it appears composed of brilliants of different sizes and shades, and sometimes, like a grand exhibition of the "northern lights," all these appearances are combined. The most phosphorescent sea seldom exhibits peculiarities by daylight. Nevertheless, sometimes, though rarely, luminous patches and even large tracts of water are seen in the daytime, and at a great distance from ordinary soundings, with the color differing materially from the well-known hue of the ocean, and seeming to indicate to the astonished mariner the existence of banks or shoals. A few days after we fell in with the Patriot privateer, being in about twenty-six degrees of latitude, in the middle of a clear and beautiful day, Mr. Campbell, who was at the helm, exclaimed, in a tone of alarm, "There's a shoal ahead!" On looking in that direction, a tract of water embracing several square miles was seen, which was of a light green color inclining to yellow. Its edges were well defined, but irregular, and presented a strong contrast with the general appearance of the ocean. We supposed the water on that spot must be shallow, but as there was a heavy swell and no breakers were seen, it was manifest there was depth of water enough for our little schooner. The deep-sea lead was got ready, and when we had reached what we considered the centre and shoalest part of the bank, no bottom was found with a hundred fathoms of line. The peculiarity in color was undoubtedly owing to luminous particles floating in the water, and if we had remained on that spot until dark we should have seen that whole tract of ocean splendidly illuminated.