If you were to go on a long voyage, there is nothing that you would be much more pleased with, than the occasional bright appearance of the sea at night. You might see this in all latitudes, but more frequently in the tropical, than in colder climates. It occurs in a variety of modes, and, as it seems, arises from several different causes. Sometimes the wake of the vessel looks like a waving line of beautiful silver light; sometimes the surface will be studded with spots of bright light, about as large as your heads; not unfrequently you may see large islands of light; and now and then a shoal of Albicores, or some other fish, will pass the vessel, shaking sparks of dazzling brightness from their fins in all directions. It has been supposed by some that the brightness in the track of a vessel, and that which sparkles and flashes in the spray on the tops of the waves, is electrical light: whether it is so or not, I cannot tell you. The effect is, no doubt, sometimes produced by decayed animal and vegetable bodies, which appear bright in the dark. I dare say you have seen the bodies of dead fish, and the surface of rotten wood have this appearance. The particles in which the brightness exists are so small, that you cannot see them, for, if you touch the luminous body, particularly if it is a stinking fish, your fingers will immediately appear bright in the dark, and when you look at them in the light, you will not be able to see anything on the surface of the skin. But the most wonderful and extensive cause of all, is the existence of countless myriads of fish and insects, which are supplied with a fluid substance that oozes out of their bodies, and shines with a greenish light upon their surface. There are a great many different forms of them, but they mostly agree in having their bodies shaped something like an umbrella, with long filaments hanging down from them. This is a picture of one of the kind called Berenice. It takes its name from the resemblance of its filaments, to the long hair of a lady. Berenice was the wife of a warrior, who made a vow to sacrifice the hair of her head, which was singularly beautiful, to Venus, if her husband returned from some successful exploit in which he was engaged. He did so, and the The substance of the body is a mere mass of jelly, mostly quite transparent, but sometimes tinged with blue or green; and when deprived of life it becomes merely a salt liquid, and an extremely thin skin, weighing only a few grains. The mouth is underneath, in amongst the filaments, which seem to be placed where they are for the purpose of entangling small fish and insects, to hold them till the Acalepha can swallow them. A very great number of them are of a kind called Medusa, from the resemblance of their filaments to the snakes, which were said to take the place of hair upon the head of Medusa, one of the Furies. One or two sorts have a crest which they erect as a sail, and thus move along before the wind, on the surface of the sea, The size varies from that of a pin's head, to a foot or more in diameter, and it is said that some have been found to weigh as much as 50 pounds. Their weight is a very little more in proportion to their bulk than that of salt water, and they keep themselves afloat on the surface, as long as they are inclined, by moving very slowly along, which they do by alternately contracting and expanding a very light ring of muscle, which surrounds the umbrella. When they are tired of their snail's gallop, or they want to descend on any other account, they There are some species peculiar to hot climates, where they are generally larger, and more luminous; and some to cold. But what is wanting in size is amply made up in number, in the Arctic regions. A certain naturalist calculated by a fair average, how many AcalephÆ there were in two square miles of sea, and the result of his calculation would fill up a whole line of this work with figures; you may judge something of it, by his saying that to count the number would have taken 80,000 persons all the time that has elapsed since the creation of the world, counting as fast as they could! It is on these creatures, most of them so small that they cannot be seen without a microscope, that the vast bodies of the whales are supported, caught in the wonderful shrimp-trap, which I described to you in a former page! Two or three kinds are found on your own It is this caustic fluid which is luminous. It oozes through the skin all round the muscular ring by which they move, and at the large filaments. The whole body of the creature looks bright, but it is only from the light transmitted by these parts. You may get a very fair notion of the appearance of one of their bodies, by rubbing together two partly transparent pebbles in the dark; the light is of nearly the same colour, and though it is only produced just at the points of contact of the pebbles, it illuminates their whole substance. As they move along they are much brighter when they contract their bodies, than when they expand them; this is because in contracting they press out the luminous fluid. I will tell you of some experiments and observations, which have been made on them. The body of an Acalepha was squeezed over a glass of warm fresh water, and the fluid that dropped out communicated its luminous property to the water. The same was then done with a glass of warm salt water, but the effect was not nearly so great. One was squeezed over a vessel containing nearly a quart of milk, which it made so resplendent that one could see to read by it. The milk retained its brightness for several hours, and when it faded, it could be restored by stirring: even three days afterwards it was made bright by being warmed. In this manner the AcalephÆ communicate a slight degree of light to the sea-water, in which I have often seen them round the ship, looking like so many moons, and emitting light enough for me to read by, some on the surface, and others at various depths below it. Their appearance was exquisitely beautiful when the weather was still and the night dark; but as I thought about it, I could not help having something of a melancholy feeling at the strange kind of half-life these creatures lead. They might enjoy themselves, but I could not tell how, for they had no sight nor hearing; they loved no light except their own selfish light; they moved about in the open sea, without seeming to enjoy their freedom, for they did not care which way they moved; they had no fixed homes or neighbourhoods to love, like the coral insects; and above all, they did not care for their kind, for they appear to come near each other only by chance as the wind or the waves may drive them. But as they were created by God, their life was given them for some wise end, and no doubt they have something to do in creation, and they are capable of enjoyment, though perhaps of nothing that would be enjoyment to us. SEPIAS |
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