AQUARIUM, a tank or vessel containing either salt or fresh water, and in which either marine or fresh-water plants and animals are kept in a living state. The name was formerly sometimes given to a tank or cistern placed in a hothouse, and intended for the cultivation of aquatic plants. The A., as now in use—originally called vivarium or aquarimrium, and intended chiefly for animals, became extremely common about 20 years ago. From 13•4 to 18GO, there was a mania for these scientific toys: they became not only an aid to study, but a source of rational amusement, depending in prin ciple upon the relations discovered by science between animal and vegetable life, and particularly upon the consumption by plants, under the action of light, of the carbonic acid gas given forth by animals, and the consequent restoration to light, air or water in which they live of the oxygen necessary for the maintenance of animal life. The A. must therefore contain both plants and animals, and in something like a proper propor tion. Zoophytes, annelides, 'nausea, crustacea, and fishes may thus, with due care, be kept in health, and their habits observed. The water must be frequently aerated, which can be accomplished by taking up portions of it and pouring them in again from a small height. The fresh-water A. is frequently provided with a fountain, which produces a continual change of water; but even where this is the case, the presence both of plants and animals is advantageous to the health of both. When sea-water cannot easily be procured for the marine A., a substitute may be made by mixing with rather less than 4 quarts of spring water 3/ ounces of common table-salt, ounce of Epsom salts, 200 grains troy of chloride of magnesium, and 40 grams troy of chloride of potas sium. With care, the water may be kept good for a long time. No dead animal or decaying plant must be permitted to remain in it. Salt water, artificially prepared, is not fit for the reception of animals at once; but a few plants must first be placed in it, for which purpose some of the green algm, species of ulva and conferva, are most suitable. The presence of a number of molluscous animals, such as the common periwinkle, is necessary for the consumption of the continually growing vegetable matter, and of the multitudinous spores (seeds), particularly of confervre, which would otherwise soon fill the water, rendering it greenish or brownish, and untransparent, and which may be seen beginning to vegetate everywhere on the pebbles or on the glass of the tank. In a fresh-water A., molluscous animals of similar habits, such as species of lymnce,a or planorlds, are equally indispensable. For large aquaria, tanks of plate-glass are commonly used; smaller ones are made of bottle-glass or of crystal.
Of course, the plants and animals with which the A. is stocked are various, according
to taste and opportunities, or the desire to make particular kinds the subjects of careful and continued observation. Blennies, gohies, and gray mullets are perhaps the kinds of fish most commonly seen in marine aquaria; gold-fishes, sticklebacks, and minnows are frequent enough in fresh-water ones. These have the advantage of being more easily kept in good health than many other kinds, and a further recommendation is found in their small size, and in the fine colors of the gold-fish. The nests of sticklebacks are a subject of unfailing interest. Crabs of various species, and actinite or sea-anemones, are very generally among the larger inmates of the A. Serpulte contribute mach both to its interest and beauty, as they spread out their delicate and finely tinted bronchhe from the mouth of their steely tube, and withdraw within it, quick as thought, upon the slightest disturbance. Balani or acorn-shells are very beautiful objects when they are seen opening their summit-valves, and rapidly stretching out and retracting their little nets. Even periwinkles and limpets are interesting, particularly when they are watched by the aid of a magnifying-glass, as they feed upon the spores of the confervie which have just begun to vegetate on the glass of the A., moving slowly along, with continual opening and shutting of the mouth, like cows at pasture, when the structure and motions of their mouths may lie observed, and the singular beauty and brilliancy of colors never fails to command admiration. The use of a good magnifying lens adds.greativ to the interest of the A., and Zoophytes of exquisite forms and colors may be watched in the actual processes of life. The feeding of fishes, crabs, sea-anemones, etc., is a source of amusement, and it is interesting even to note how the inmates of the A. occasionally feed on their fellow-prisoners.
The idea of the A. seems to have originated from Mr. Ward's invention of the cases which bear his name (see WAnDrAsz CASES), and in which delicate ferns and other plants grow's° well even in towns; but the late Sir John Graham Dalzell begun to keep living marine animals in his house in Edinburgh so early as 1790, and continued to do so till the year 1850. Mr. Warrington appears to have been the first to make experiments on its practicability, and the name of Mr. Gosse is intimately associated with its early development and introduction to popularitTas a scientific plaything. A Mr. Price also conducted some very successful experiments as to the balance of animal and vegetable life in aquaria. The largest aquaria in the world are those at Brighton and Hamburg, and there is also one of large dimensions at the Crystal palace, Sydenham, as well as others in various parts of England, and in Scotland.