The luminous appearance of the sea, so often mentioned by voyagers, is, especially within the tropics, very beautiful and interesting, and depends in a great measure upon the presence of minute Crustacea—such as the Entomostraca more particularly—and Medusa?, the different kinds of animal producing a different kind of luminousness. This I may illustrate by an extract or two from a journal kept during a voyage to India.
"May 28, 1832, lat, 1° 50' N. long. 24° 07' W. In the evening the sea, especially in the wake of the ship, where the water was agitated by the ship's way through it, was splendidly luminous; it presented a truly brilliant appearance at times, for the beautiful brilliancy of the luminousness was not equal at one time to what it was at another.—Sometimes the broad bright flash, which had distinctly occasionally a bluish colour, was vivid enough to illuminate the sea for some distance round, while the most splendid globes of fire were seen wheeling and careering in the midst of it, and by their brilliancy outshining the general light. These bodies were generally too deep in the water to be caught by throwing a bucket or net overboard.
"May 29. Lat. 0° 35' S. long. 26° 02' W. The sea was very luminous again this evening, but differed from last night in there being fewer large globes deep in the water, and a much greater abundance of bright small specks on the surface. Drawing a bucket-full of water up, about 8, P.M., I allowed it to remain quiet for some time, when upon looking into it in a dark place, the animals could be distinctly seen emitting a bright speck of light. Sometimes this was like a sudden flash, at others appearing like an oblong or round luminous point, which continued bright for a short time, like a lamp lit beneath the water, and moving through it, still possessing its definite shape, and then suddenly disappearing. When the bucket was sharply struck on the outside, there would appear at once a great number of these luminous bodies, which retained their brilliant appearance for a few seconds and then all was dark again. They evidently appeared to have it under their own will, giving out their light frequently at various depths in the water, without any agitation being given to the bucket. At times might be seen minute but pretty bright specks of light dart across a piece of water, and then vanish, the motion of the light being exactly that of the Cyclops through the water. Upon re-
