Aquarium, Or Aquavivarium, a term applied to certain artificial arrangements for the exhibition and study of living animals and plants inhabiting either fresh or salt water. To Mrs. Power, a lady of French descent, belongs the credit of first adopting the aquarium as an aid to scientific research. This intelligent and enthusiastic naturalist, during the year 1832, began the study of the fishes and algae off the coast of Sicily, by transferring them to glass tanks in which the water was often renewed; and this renewal or revivification of the water was long regarded as essential to the health and vigorous growth of the inmates, it being argued that as the air is contaminated by the breathing of animals living upon the surface, and its oxygen is combined with the carbon furnished by the organic body, so the air con- tained in the water is consumed by administer- ing to animal life, and the gaseous product is not only unfit for longer sustaining this, but, unless removed, proves fatal to it.

But subsequent investigations into the various phenomena of vegetable and animal growth have determined that it is the office of plants to restore to the atmosphere the oxygen, and absorb the excess of carbon; and it appears that the subaqueous vegetation fulfils the same office in preserving the purity of the air in the water, upon which depends the life of the animals it contains; and that this balance may not be destroyed by the presence of poisonous gases, the results of decomposition and decay, it was found needful to add certain animals which feed on decomposing vegetable matter, and act as the scavengers in this community. Such are the various species of the molluscous animals, as the snails. It is also of importance to guard against the preponderance of animal life in these artificial tanks or jars; for although there can hardly be too many plants for the health of the animals, as long as they grow healthily and do not decompose, yet an excess of animals over plants will disturb the balance, and lead to the destruction of the former.

Valisneria spiralis, various species of chara, anacharis alsinastrum, stratiotes aloides, callitriehe autumnalis or vernalis, ranunculus aquatilis, and myriophyllum spicatum are among the fresh-water plants adapted to this purpose. - The fresh-water aquarium is more easily constructed and requires less skilful management than the marine tank. It should be square or hexagonal, as curved surfaces distort the forms of the inmates, and a greater number of sides increases the liability to leakage. Where metal corner posts are used, they should be plated if possible, as the oxidation of the metal often results disastrously. The glass plates should be held in position by hydraulic cement; that known as Scott's is highly recommended. Where putty only is available, it should be painted, the tank filled with water for a week or more, and then carefully cleaned before receiving the fishes and plants. The bottom should be covered to a depth of an inch or more with well washed river sand, and its surface thickly strewn with pebbles; clay or mould should be avoided, both because of the vegetable germs it may contain, and because its frequent disturbance by the fish renders the water turbid.

The use of tastefully arranged rockwork adds greatly to the beauty; but rocks containing metallic substances should be rejected; and where shells are used, they should first be well soaked or calcined in order to destroy all organic matter contained in them. In constructing these arches or columns Portland cement may be used to advantage, and some point of the structure should project above the water level. Thus arranged, the tank, which should be at least 12 inches deep, may be filled with fresh spring or river water to within an inch of the top, and it is then ready for occupation. Such fresh-water plants as the butomus, nymphaea, and alisma should have their fibrous roots extended and gently imbedded in the sand, with a layer of pebbles to keep them in position. All river plants that bud and root from points on the stem, as anacharis, ranunculus, callitriehe, and chara, can be raised by securing them in tufts to the sandy bottom by a light layer of pebbles. There are certain plants which, in addition to beauty of structure and vigorous growth, are of great service as oxygen producers; such are the valisneria spiralis, water thyme (anacharis alsinastrum), with the flowering water crowfoot (ranunculus aquatilis), milfoil, and starwort. - Though the stocking of the aquarium depends largely upon the purpose it is to serve, yet caution is needed as to the number and habits of the inmates.

A young pickerel only an inch and a half long has been known to devour 25 minnows in a week. For general interest, the stickleback takes the lead among the fishes, and for beauty the gold fish, tench, gudgeon, perch, minnow, and Prussian carp all flourish, with snails and mussels as purifiers. Where the proper balance is not easily maintained and the renewal of the water is difficult, it may be revivified by dipping out and pouring back in a small stream from a proper height. As in the marine tank, an excess of sunlight is apt to encourage the growth of a minute green fungus, besides unduly elevating the temperature, which should range between 40° and 60° F. - The marine tank, owing to its greater range, and the extreme sensitiveness of its animals and plants, requires more constant and careful management. As a rule it should be more shallow. To secure this, and also obtain sufficient depth of water for fish and hardy plants, a tank having its back and two ends opaque has been successfully adopted, in which case these may be of the same material as the bed plate - marble, slate, or well seasoned wood. The front is of glass, and the bottom an inclined plane rising from the lower corner in front to above the water level behind; on this rest the rock and shell work.

The triangular space between the front and this plane may be filled to the depth of an inch or two with sand and gravel, with a sprinkling of the same among the rocks and shells above. The purpose of this sloping floor is to afford the anemones, actiniae, etc, which move seldom and slowly, to approach the surface and recede from it at pleasure. Marine plants purify sea water, as freshwater plants purify fresh water. The difficulties of maintaining the balance are, however, greater in sea-water artificial tanks than in fresh-water; but by care in selecting seaweeds, avoiding those which are large and throw off much matter from their surface, and not overcrowding the water with animal life, tanks containing marine aquatic animals and plants can be easily managed. Species of porphyra, cliondrus, crispus, iridea edulis, and the delesseriae are recommended. - Where vegetation is only needed for the production of oxygen, Mr. Shirley Hibberd, the author of a useful handbook on the aquarium, recommends the encouragement of confervoid growth; and where sea water is used, the germs contained in it will soon, under the light and warmth of the sun, develop into a vigorous and serviceable vegetation.