a term frequently met with in the writings of physicians, chemists, &c. for certain medicines, or menstruums, in a liquid form, distinguished from each other by peculiar epithets, as Aqua Alexiteria, Aqua Alumina, Aqua Mirabilis, &c. for which see PHARMACY.

Aqua Extincta, or Extinguished Water, as aquafortis into which some river-water has been poured, in order to qualify it, and render it less corrosive. Its use is to get the silver from the aquafortis that served to part gold from it.

Aqua Fortis, a name given by artists to nitrous acid of a certain strength, from its dissolving power; that which is concentrated and smoking, is called spirit of nitr. The aquafortis used by dyers, brass-founders, &c. is not only weaker than spirit of nitre, but contains a portion of vitriolic acid. It may be made by distilling crude nitre with calcined vitriol, equal parts. The nitrous acid, expelled by the vitriolic, will rise in red fumes, and pass into the receiver. The vitriolic acid, uniting with the alkaline basis of the nitre, forms vitriolated tartar; but, there being more vitriolic acid than is requisite to saturate the alkali, the surplus rises with the nitrous acid: aquafortis, therefore, is a mixture of these two acids. It may also be made by distilling crude nitre with somewhat more than half its weight of oil of vitriol; or by mixing one part of oil of vitriol with nine parts pure spirit of nitre. See CHEMISTRY-INDEX.

Aqua Marina, a name by which the jewellers call the beryl, on account of its sea-green colour. See BERYL.

Aqua Regia, a compound of nitrous and marine acid, in different proportions according to the purpose for which it is intended. It is usually made by distilling, in nitrous acid, sal ammoniac, or common salt, both which are combinations of marine acid with alkali. When made with sal ammoniac, the common proportion is one part of this salt to four parts of nitrous acid; but to dissolve platinum, equal parts are requisite. A purer aqua regia may be made by simply mixing the two acids.

Aqua regia is particularly used as a menstruum for gold; it likewise dissolves all other metals, except silver. The gold dissolved in aqua regia is, in fact, dissolved in the dephlogisticated marine acid only, which, being deprived of its phlogiston by the nitrous acid, recovers it from the gold, and thus renders gold fusible; for metals are not fusible in acids until they lose a part of their phlogiston. See CHEMISTRY-INDEX.

Aqua Secunda, aquafortis diluted with much pure water. It is employed in several arts, to clean the surface of metals and certain stones, and for various other purposes.

Aqua Vitæ, is commonly understood of what is otherwise called brandy, or spirit of wine, either simple, or prepared with aromatics. Some, however, distinguish between them; appropriating the term brandy to what is drawn from wine, or the grape; and aqua vitae to that drawn after the same manner, from malt, &c.

Aqua Augusta, (Ptolemy); Aqua Tarbellica, (Antonine); Aquensis Civitas, in the Notitia. Now Acqs, or Dax, a town in Gascony, on the river Adour, famous for its baths. W. Long. 1. 40. N. Lat. 43. 56.

Aqua Bilbiliana, (Antonine); baths 24 miles to the west of Bilbilis. Now Banos de Aibana, in Aragon.

Aqua Calida, (Ptolemy); Aqua Solis, (Antonine); a place of the Belgæ in Britain, famous for its hot waters. Now Bath, in Somersetshire. W. Long. 1. 5. Lat. 51. 20.

Aqua Calida, (Ptolemy); Aquicaldensis, (Pliny); formerly in great repute, and a public bath; whose ruins still remain testimonies of the Roman grandeur. Now Orense, in Galicia, still famous for its baths; on the river Minho, 54 miles south-east of Compostella. W. Long. 8. 30. Lat. 42. 30. Also a place in the bay of Carthage, (Strabo). Other Aquicaldensis, to the north of Gerunda in Catalonia, (Ptolemy).

Aqua Calida, a colony between the rivers Serbetes and Savus, in Mauritania Caesariensis, (Ptolemy).

Aqua Celeris, (Ptolemy); or Cilina, (Antonine). Now Caldas, a hamlet on the Minho, in Galicia.

Aqua Convenarum, a hamlet of Gaul, in Aquitaine, (Antonine), and on the borders of the Convenae, or le Cominge, at the foot of the Pyrenees, near the source of the Garonne. Now Bagnères. W. Long. 5. 39. Lat. 42. 20.

Aqua Cutiliae, a lake of the Sabines, in the territory of Reate (Pliny); Lacus Cutiliensis, (Varro); with a moveable island in it, (Seneca, Pliny); supposed to be the centre of Italy, (Varro). The waters were medicinal, and extremely cold, good for a weak stomach and in weak nerves; they seemed to act by a kind of suction, which approached to a bite, (Pliny). Vespasian used them every summer; and there he died, (Tacitus, Xiphiius from Dio). Now Lago di Contigliano.

Aqua Flavie, a town on the confines of Gallicia and Portugal, so called from Vespasian and Titus. The inhabitants are called aquiflavienesi, coins. Now called Chiaves, a mean hamlet; but the ruins of its bridge testify its former grandeur. W. Long. 6. 6. Lat. 41. 40.

Aqua Helvetica, described by Tacitus as a municipal town, and much frequented for its excellent water, and though he does not mention its name, Cluvierius sup- Aqueduct supposes it to be Baden, in Switzerland, on the rivulet Limat, which soon after falls into the Aar. It is called the Upper, to distinguish it from another called the Lower Baden, in Alfae. E. Long. 8. 49. Lat. 47. 55.

Aquae Merom (Joshua), famous for the defeat of Jabin; supposed to be the lake called Samachonitis, or Semonchonitis, by Josephus; into which the river Jordan falls, before it comes to the sea of Genesereth, or Galilee.

Aquae Pannoniae famous baths of Austria, now called Baden, 28 miles to the south of Vienna.

Aquae Patavinae, are baths in the territory of Venice near Padua, (Pliny); called Fentes Aponi (Livy, Martial). Now Bagni d'Abano. E. Long. 13. 48. Lat. 45. 15.

Aquae Quintianae, put by Ptolemy in room of the Aquae Cilinae of Antonine. Now supposed to be Sarria, a town of Gallicia, on a rivulet of the same name, three leagues to the south of Lugo.

Aquae Sextiae, a colony to the north of Marcellae, so called, both from the founder Sextius Calvinius, and from its quantity of water, and number of cold and hot springs; built after the defeat of the Salyes, or Salvi, whose territory in the south of Provence reached from the Rhone to the borders of Italy, (Livy, Velleius, Strabo, Ptolemy). By an inscription the colony appears to have been either increased or renewed by Augustus. In the Notitia it is called Civitas Aquensis. Now Aix. Here the Teutones and Cimbri were defeated with a great slaughter by Marius. E. Long. 6. 4. Lat. 48. 4.

Aquae Statillae, or Statiellorum, (Pliny), a town in Liguria, on the river Bornia. Now Acqui, a town of Montferrat. E. Long. 8. 40. Lat. 44. 45.

Aquae Tauri, hot waters or baths in Tuscany, at the distance of three miles from the sea, said to be discovered by a bull, hence the appellation. There are still to be seen the ruins of these baths. Now Acquapendente, in Orvieto. E. Long. 12. 40. Lat. 42. 40.

Aqueduct, in hydraulics and architecture, a structure formed for conveying water from one place to another, over grounds that are unequal. The word is compounded of the Latin substantive aqua water, and ductus a channel by which that water may be conducted.

Architects distinguish two kinds of aqueducts; the visible, and the subterraneous.—The visible are constructed in valleys or marshes, and protracted in longitude or latitude as the situation requires. They are composed of arches for supporting the arches and confining the stream, and of arcades.—The subterraneous are formed, by piercing the mountains, and conducting them below the surface of the earth. They are built of stone, hewn or rough; and covered above with vaults, or with flat stones, which may be termed flags; these flags shelter the waters from the heat of the sun.

They divide them still into double and triple aqueducts; that is to say, such as are supported either by two or by three ranges of arcades. Such was the aqueduct which Procopius records to have been built by Cofroes king of the Persians, for the city of Petra in Mingrelia: it had three conduits upon the same line, each elevated above the other.

Frequently aqueducts are paved. Sometimes the waters flow through a natural channel of clay. Frequently they are conveyed by pipes of lead into reservoirs of the same metal, or into troughs of hewn stone. The channels are cut with an imperceptible descent, that the current may be accelerated by its own weight. Parallel to its course, on each side, is cut a narrow footpath, where people may walk when necessary. By conduits, or grooves, the waters are conveyed into large cisterns, but not forced above their original level. To make them rise and issue from their apertures with force, they must be confined in tubes of a small diameter, and abruptly fall from a considerable declivity.

Aqueducts of every kind were long ago the wonders of Rome; the vast quantity of them which they had; the prodigious expense employed in conducting waters over arcades from one place to another, at the distance of 30, 40, 60, and even 100 miles, which were either continued or supplied by other labours, as by cutting mountains and piercing rocks; all this ought to surprise us; nothing like this is undertaken in our times; we dare not even think of purchasing public convenience at so dear a rate. Appius the censor advised and constructed the first aqueduct. His example gave the public luxury a hint to cultivate these objects; and the force of prodigious and indefatigable labour diverted the course of rivers and floods to Rome. Agrippa, in that year when he was edile, put the last hand to the magnificence of these works. It is chiefly in this respect that the modern so much resembles the ancient city of Rome. For this advantage, he is peculiarly indebted to Sextus V. and to Paul V. who for grandeur and magnificence emulated the masters of the universe*. There are still to be seen, in different places contiguous to Rome, striking remains of these aqueducts; arches continued through a long space, over which the water was extended the canals which carried the water to the city. The arches are sometimes low, sometimes raised to a vast height, to humour the tumidities or depressions of the ground. There are some which have two arcades, one constructed above the other; and this precaution was observed, lest the height of a single arcade, if extended as far as the situation required, might render the structure less firm and permanent. They are commonly of bricks; which by their cement cohere strongly, that the parts are not separated without the utmost difficulty.—When the elevations of the ground were enormous, it became necessary to form subterraneous aqueducts. These carried the waters to such aqueducts as were raised above ground, in the declivity or at the foot of mountains. If the artificial channel of the water was not susceptible of a downward bias but by passing through a rock, through this they cut a passage at the same height with the superior aqueduct: such an one may be seen above the city of Tivoli, and at the place called Vicovaro. The canal which formed the course of the aqueduct is hewn out of the rock to the extent of more than a mile, about five feet in height and four in breadth.

There is one thing, however, which deserves to be remarked. It is, that these aqueducts, which might have been directed in a straight line to the city, did not arrive at it but by frequent and winding mazes. Some have said that this oblique tract was purposed to avoid the expense which must attend the building of arcades to an extraordinary height: others, that it was their intention to diminish the impetuosity of the current, which,