The cause of this singular phenomenon has given rise to many theories and much discussion among naturalists. It was for a time contended that this phosphorescence was a quality of the water itself. But later and more accurate observers ascertained beyond a doubt, that some marine worms and other insects were luminous. On pursuing the investigation it is ascertained that the sea water is far less pure than has been supposed, and is often crowded with myriads of minute luminous animals. It is now admitted that the phosphorescence of sea water is a property not belonging to itself, but is produced by animalcula, or microscopic creatures. They are far more numerous in some tracts of ocean than in others, and all possess the power of producing a light, a spark, or flash at will. There can be no doubt that these living, transparent atoms cause the luminous appearance of the ocean, which excites admiration, and has so often been described in glowing language by the poet. Chapter XXII. CAPTURED BY A PRIVATEER Captain Moncrieff was desirous of entering the Caribbean Sea through the Sail-rock passage, which separates the barren island of St. Thomas from Porto Rico. But when we reached the latitude of those islands we beheld, on our starboard bow, the mountainous country on the eastern part of Hayti. The island of Porto Rico was soon afterwards seen on the other bow, and directly ahead was the little island of Mona, rising abruptly from the sea. Instead of striking the Sail-rock passage we found ourselves in the centre of the Mona passage, a hundred and twenty miles to leeward of Sail-rock, and twenty or thirty miles westward of the meridian of LaGuayra. Although Captain Moncrieff was glad of an opportunity to ascertain his true position, he was mortified at finding himself westward of his destined port. The Young Pilot was immediately hauled on a wind, and we crossed the Caribbean Sea with a fine breeze, and one morning beheld the Rocas, a cluster of barren rocks, right ahead. We passed over a bank extending from this group of rocks, and with a fishing-line trailing astern and a piece of the rind of pork for bait, caught a quantity of Spanish mackerel, a fish of excellent flavor, weighing four or five pounds each. And I will here state, for the benefit of those navigators who have little experience in those seas, that on the edge of soundings in all parts of the West Indies, and particularly on the edges of the Bahamas and Salt Key Bank, abundance of fish of excellent quality, as black perch, kingfish, barracooter, and Spanish mackerel, may be taken by trailing during a breeze, in any reasonable quantity.