several of these threads, till one is produced capable of supporting it in the air: and this it mounts in quest of prey, and frequently rises to a very considerable height.

AIR-VESSELS, ducts in the leaves and other parts of plants, supposed to convey air to the vegetable system, as the lungs do to the animal.

́ ́AJUTAGE, or ADJUTAGE, in hydraulics, part of the apparatus of a jet d'eau, or artificial fountain; being a kind of tube fitted to the aperture or mouth of the cistern, or the pipe; through which the water is to be played in any direction, and in any shape or figure.

It is chiefly the diversity in the ajutage, that makes the different kinds of fountains. So that, by having several ajutages, to be applied occasionally, one fountain is made to have the effect of many.

of

It has been found that jets do not rise quite so high as the head of water; owing chiefly to the resistance of the air against it, and the pressure the upper parts of the jet upon the lower: and for this reason it is, that if the direction of the ajutage be turned a very little from the perpendicular, it is found to spout rather higher than when the jet is exactly upright. It is found by experiment too, that the jet is higher or lower, according to the size of the ajutage: that a circular hole of about an inch and a quarter in diameter, jets highest; and that the farther from that size the worse. Experience also shews that the pipe leading to the ajutage should be much larger than it; and if the pipe be a long one, that it should be wider the farther it is from the ajutage.

ALABASTER, a stone whose basis is calcareous

+

earth. Its fineness and transparency renders it in some measure transparent. There is a church at Florence illuminated by alabaster windows: instead of panes of glass, it has slabs of alabaster, nearly fifteen feet high, each of which forms a single window. In the German province of Hohenstein, a kind of laminated alabaster is found in great abundance, beautifully variegated with the figures of trees, shrubs, and sprays.

ALARUM, any contrivance for the purpose of alarm. A bell, or rattle, to call assistance. A bell fastened to, or communicating with, a door or window. A piece of mechanism is sometimes affixed to clocks, by means of which a noise is made at any required time. At the royal observatory, at Greenwich, the deputy astronomer is by this means roused at all hours of the night, to make the necessary observations ; and the same method is resorted to by persons desirous of rising at unusual ⚫ times. The slug-a-bed (or lig-a-bed), however, can easily render the alarum of no avail. A fellow of one of the colleges of Oxford, desirous of overcoming his indolence, had procured an alarum. It was a weight, that at a given hour, descended with rapidity from a clock in his chamber. The alarum descended, and the ly-a-bed awoke; but still he rose no earlier than before. In this dilemma, by an addition of his own, he rendered the alarm complete. He had a china bowl, the gift of a friend whom he highly valued: this he placed under the alarum; and now he was obliged to spring up at the instant of summons, lest the weight should demolish his relic.

ALBINO, the name given by the Portuguese to a

white Moor; that is, one who is afflicted with the nyctalopy. The term is sometimes applied to such Europeans, as have the same constitutional a imperfections. See Nyctalopy.

ALBUMEN, in its primitive sense, signifies the white of an egg; but it is now applied to one of the constituent parts of vegetable bodies, exactly resembling this animal substance.

ALBURNUM denotes the white soft substance that lies between the inner bark and the wood of trees, composed of layers of the former, which have not attained the solidity of the latter. A new layer of alburnum is added annually to the tree in every part, just under the bark, and the former layer of . alburnum becomes perfect wood.

ALCHEMY, or Alchemistry, is properly applied to the higher pursuits of chemistry, as The chemistry, by way of eminence; but the name has become obsolete on account of two objects, which speculators hoped for, and impostors, by its means, pretended to have acquired. These were, 1. The philosopher's stone, by which all metals might be transmuted into gold; and, 2. A potation, called the elixir of life, with which youth might always be renewed.

: ALCOHOL, an Arabian word, signifying any thing reduced into extremely thin parts, or rendered extremely subtle by distillation. The word, at present, is used for a highly rectified spirit. This preparation is extremely light and inflammable: it is colourless and transparent, appearing to the eye like pure water. To the taste it is exceedingly hot and burning: but without any peculiar staste. From its lightness, the bubbles which are

formed by shaking, subside almost instantaneously which is one method of judging of its purity. Alcohol boils at 165°: but it cannot be frozen or converted from the fluid to the solid form, and on this account, it has been much used in the construction of thermometers. It is employed as a solvent for resinous gums, which form the basis of varnishes. Its antiseptic power renders it valuable in preserving animal substances.

ALCORAN. See Korun.

ALDERMAN, among our Saxon ancestors, was a degree of nobility, from which is derived the earl of the present day. Modern aldermen form the principal branch of a town or city corporation. Their number is not limited, but differs according to the magnitude of the place, where they exercise the authority of commissioners of the peace. In London, their number is twenty-six; each having a ward, or district of the city committed to his more peculiar care; but, serving by rotation, as sitting magistrate for the whole. The office is for life, or for so long as the individual chooses to retain it. When a vacancy happens, through death or resignation, the livery of the ward are assembled, or, to use the peculiar term, a ward-mote is held; a new alderman is chosen, whom the lord mayor returns to the other aldermen, in the court of the lord mayor and aldermen, where the person so returned must be admitted, and sworn into the office, before he can act. If the person elected refuses to wear the gown, he is liable to a fine of 500 7. Aldermen are exempted from inferior offices; from being put upon assizes; or from serving on juries. In the present day persons are not

fined for refusing to take the gown; the honour is an object of great and anxious contest: but owing, it is supposed, to some recent failures in the city of London, it has been determined that no person shall be admitted to take the gown who cannot swear that he has property equal to 30,000l.

ALECTOROMANTIA. An ancient kind of divination by means of a cock, called also Alectryomancy; of which there appear to have been different species. But that most spoken of by authors was in the following manner: A circle being described on the ground, and divided into 24 equal portions, in each of these spaces was written one of the letters of the alphabet, and on each of the letters was laid a grain of wheat; after which a cock being turned loose in the circle, particular notice was taken of the grains picked up by the cock, because the letters under them, being formed into a word, made the answer desired. It was thus, according to Zonaras, that Libanius and Jamblicus sought who should succeed the emperor Valens; and the cock eating the grains answering to the spaces EOA, several whose names began with those letters, as Theodotus, Theodistes, Theodulus, &c. were put to death, which did not hinder, but promote, Theodosius coming to the succession.

ALEMBIC. One of the simplest and most ancient vessels employed in distillation. It is not at present much used in England; the retort and still having been adopted in its stead; but in France and many parts of the continent, it continues to be the favourite vessel for distillations in the large way. The most frequent use of alembics is for distillations of very volatile principles drawn from several sub