AQ´UAMARINE, a name given to some of the finest varieties of beryl of a sea-green or blue colour. Varieties of topaz are also so called.
AQUA´RIUM, a vessel or series of vessels constructed wholly or partly of glass and containing salt or fresh water in which are kept living specimens of marine or fresh-water animals along with aquatic plants. In principle the aquarium is based on the interdependence of animal and vegetable life; animals consuming oxygen and exhaling carbonic acid, plants reversing the process by absorbing carbonic acid and giving out oxygen. The aquarium must consequently be stocked both with plants and animals, and for the welfare of both something like a proper proportion should exist between them. The simplest form of aquarium is that of a glass vase; but aquaria on a larger scale consist of a tank or a number of tanks with plate-glass sides and stone floors, and contain sand and gravel, rocks, sea-weeds, &c. By improved arrangements light is admitted from above, passing through the water in the tanks and illuminating their contents, while the spectator is in comparative darkness. The most important aquarium is at the zoological station at Naples. There is also one, on a smaller scale, at Plymouth, maintained by the Marine Biological Association of the United Kingdom. Aquaria on a large scale have been constructed in connection with public parks or gardens, and the name is also given to places of public entertainment in which large aquaria are exhibited.--Cf. G. C. Bateman, _Fresh-water Aquaria_; M. J. Newbigin, _The Aquarium_.
AQUARIUS (Lat., the Water-bearer), a sign of the zodiac which the sun enters about the 21st of Jan.: it now enters the formerly coincident constellation Aquarius about a month later.
AQUATINT, a method of etching on copper by which a beautiful effect is produced, resembling a fine drawing in sepia or Indian ink. The special character of the effect is the result of sprinkling finely-powdered resin or mastic over the plate, and causing this to adhere by heat, the design being previously etched, or being now traced out. The nitric acid (aqua fortis) acts only in the interstices between the particles of resin or mastic, thus giving a slightly granular appearance.