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.
Aqua Tofa´na. See Aqua.
Aqua vitæ. See Aqua.
Aq´ueduct (Lat. aqua, water, duco, to lead), an artificial channel or conduit for the conveyance of water from one place to another: more particularly applied to structures for conveying water from distant sources for the supply of large cities. Aqueducts were extensively used by the Romans, and many of them still remain in different places on the Continent of Europe, some being still in use. The Pont du Gard in the south of France, 14 miles from Nîmes, is still nearly perfect, and is a grand monument of the Roman occupation of this country. The ancient aqueducts were constructed of stone or brick, sometimes tunnelled through hills, and carried over valleys and rivers on arches. The Pont du Gard spans the River Gard, and was built to convey to Nîmes the water of springs rising in the neighbourhood of the modern Uzés. It is built of great blocks of stone; its height is 160 feet; length of the highest arcade, 882 feet. The aqueduct at Segovia, originally built by the Romans, has in some parts two tiers of arcades 100 feet high, is 2921 feet in length, and is one of the most admired works of antiquity. One of the most remarkable aqueducts of modern times is that constructed by Louis XIV for conveying the waters of the Eure to Versailles. The extensive application of metal pipes has rendered the construction of aqueducts of the old type less necessary; but what may be called aqueduct bridges are still frequently constructed in connection with canals and also with water-works for the supply of towns. Where canals exist canal aqueducts are common, since the water in any section of a canal must be kept on a perfect level.
Many large towns now derive a supply of water from sources at a great distance, and in
bringing the water to the place where it is required much tunnelling is often necessary as well as digging and excavating in the open. A tunnel furnishing a water channel may be driven through miles of rock strata of various kinds, and in many places it may have to be lined with concrete or cement wholly or partially, brick-work also being much employed. Instead of tunnelling, the channel may be formed on the plan of 'cut and cover', being first cut in the ground and then covered over, leaving the surface much in the same state as before. And, of course, iron piping is often used in connection with such tunnels, the water being conveyed so far in an aqueduct of one kind, and so far in one of another kind, according as is deemed most suitable. In the Thirlmere aqueduct, which brings water to Manchester, there are 45 miles of cast-iron pipes, 37 miles of cut-and-cover work, and 14 miles of tunnels proper. Pipes are naturally laid where valleys occur, and the water simply enters the pipes at one end and flows out at the other by the influence of gravity, there being a suitable chamber constructed at either end of the pipe line where there is a junction with a section of tunnel. Aqueduct bridges were first introduced into England in the eighteenth century, the first being the aqueduct at Barton Bridge conveying the Bridgewater Canal across the Irwell. In such bridges the water-channel may be made of cast iron. There are great aqueduct bridges on some of the Indian canals, such as the Nadrai bridge on the Lower Ganges Canal. In America water is often carried long distances in flumes or open wooden channels, supported, where necessary, on trestles. Great wooden pipes are also common there, built of large staves and hooped round with iron or steel. These often rest on the surface of the ground without any covering.—Bibliography: C. Herschel, Frontinus; Wegmann, Water-supply of City of New York; J. F. Bateman, The Manchester Waterworks; J. M. Gale, The Glasgow Waterworks; A. Prescott Folwell, Water Supply Engineering.