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The first letter of the alphabet, and one 2 of the five vowels, is pronounced variously; sometimes open, as in the words talk, trar; and at others close, as in take, take. A is also tised, on many occasions, as a character, mark, or abbreviation. Thus, in the calendar, it is the first of the dominical letters: among logicians, it denotes an universal affirmative proposition: as a numeral, A signified 1 among the Greeks; but among the Romans, it denoted 500, and with a dash over it, thus A, 5000. A, a, or aa, among physicians, denote ana, or an equal weight, or quantity, of several ingredients. AAM, or HAAM, a liquid measure used by the Dutch, equal to 288 pints English In easure. ABACK, in sea language, signifies the *tuation of the sails when their surfaces are flatted against the mast. They may be brought aback, either by a sudden change of wind, or an alteration in the ship's course. They are laid aback to effect an immediate retreat, without turning either to the right or left, to avoid some immediate danger in * narrow channel, or when she has advanced beyond her station in the line of battle. ABACUS, in architecture, the uppermost member of the capital of a column. See Architecture. Abacus, among ancient mathematicians, was a table strewed over with dust, or

*and, on which they drew their figures or

*chemes. ABAcus, in arithmetic, an instrument for *ilitating operations by means of counters. * form is various; but that chiefly used "...of is made by drawing parallel

M. f.


lines, distant from each other at least twice the diameter of a counter; which, placed on the lowermost line, signities 1; on the second, 10; on the third, 100; on the fourth, 1000; and so on. Again, a counter, placed in the spaces between the lines, signifies only the half of what it would do on the next superior line. ABAcus pythagoricus, a multiplicationtable, or a table of numbers ready cast up, to facilitate operations in arithmetic. - ABAcus logisticus, is also a kind of multiplication-table, in form of a right-angled triangle. ABAcus harmonicus, among musicians, denotes the arrangement of the keys of a musical instrument. ABAcus, Grecian, an oblong frame, over which are stretched several brass wires, strung with little ivory balls, by the various arrangements of which all kinds of computations are easily made. ABAcus, Chinese, or Shwanpan, consists of several series of beads strung on brass wires, stretched from the top to the bottom of the instrument, and divided in the middle by a cross piece from side to side. In the upper space every string has two beads, which are each counted for five; and in the lowest. space every string has five beads, of dif. ferent values, the first being counted as 1, the second as 10, the third as 100, and so on. ABAFT, in sea-language, a term applied to any thing situated towards the stern of a vessel: thus a thing is said to be abaft the fore-mast, or main-mast, when placed be tween the fore-mast, or main-mast, and the stern.

Ab Aft the beam, denotes the relative situation of any object with the ship, when the object is placed in any part of that arch of the horizon which is contained between a line at right angles with the keel, and that point of the compass which is directly opposite the ship's course. ABAS, a weight used in Persia for weighing pearls, being one-eighth part lighter than the European carat. , ABASED, in heraldry, is said of the wings of eagles, &c. when the tip looks downwards to the point of the shield, or when the wings are shut; the natural way of bearing them being spread. ABATE, in law, signifies to break down or destroy, as to abate a nuisance, and to abate a castle. It means to defeat and overthrow, on account of some error or exception. ABATEMENT, in heraldry, something added to a coat of arms, in order to lessen its true dignity, and point out some imperfection or stain in the character of the person who bears it. ABATEMENT, in law, signifies the rejecting a suit, on account of some fault either in the matter, or proceeding. Hence, plea in abatement is some exception alleged, and proved, against the plaintiff's writ, declaration, &c. and praying that the plaint may abate or cease; which being granted, all writs in the process must begin de moro. ABATOR, in law, one who enters into a house or lands, void by the death of the last possessor, before the true heir; and thereby keeps him out, till he brings the writ intrusione. ' ABDOMEN, in anatomy, the lower part cf the trunk of the body, reaching from the thorax to the bottom of the pelvis. See AN Atomi Y. A Bloo MINALES, in natural history, an order of fishes, having ventral sins placed behind the pectoral in the abdomen, and the branchia ossiculated. This order comprehends sixteen genera, viz.

Amia Cobitis Atherina Chipea Esox Cyprinus Elops Loricaria Exocoetus Fistularia Salmo Mugil Polymemas Teuthis Silurus Argentina

ABDUCTOR, or Abduce Nt, in anatomy, a name given to several muscles on account of their serving to withdraw, open, or pull back the parts to which they are sixed. See ANAto M Y.

ABERRATION, in astronomy, an ap

parent motion of the heavenly bodies, produced by the progressive motion of light and the earth's annual motion in her orbit. Since light proceeds always in right lines. when its motion is perfectly undisturbed, if a fine tube were placed so as to receive a ray of light, passing exactly through its axis when at rest, and then, remaining in the same direction, were moved transversely with great velocity, it is evident that the side of the tube would strike against the ray of light in its passage, and that, in order to retain it in the axis, the tube must be inclined, in the same manner as if the light. instead of coming in its actual direction, had also a transverse motion in a direction contrary to that of the tube. The axis of a telescope, or even of the eye, may be considered as resembling such a tube, the passage of the light through the refracting substances not altering the necessary inclination of the axis. In various parts of the earth's orbit, the aberration of any one star must be different in quantity and in direction; it never exceeds 20" each way, and therefore insensible in conimon observations. If AB and AC (Plate Acoustics, &c. fig. 1,) represent the comparative velocity of light and of the earth, in their respective directions, a telescope must be placed in the direction BC in order to see the star D, and the star will appear at E. This discovery was made by Dr. Bradley, in his observations to determine the annual parallax of the . fixed stars, or that which arises from the motion of the earth in its orbit round the sun. AberRAtion of the planets, is equal to the geocentric motion of the planet, the space which it appears to move, as seen from the earth, during the time that light employs in passing from the planet to the earth. This with regard to the sun, the aberration in longitude is constantly 20", which is the space moved by the earth in the time 8' 7", which is the time that light takes to pass from the sun to the earth. Hence the distance of the planet from the earth being known, it will be, as the distance of the sun is to the distance of the planet, so is 8' 7" to the time of light passing from the planet to the earth; then computing the planet's geocentric motion in this time, will give the aberration of the planet, whether it be in longitude, latitude, right ascension, or declimation. The aberration will be greatest in longitude, and but very small in latitude, because the plane's deviate very little from the plane of the ecliptic. In Mercury it is only 4}", and much less in the other planets. The aberration in declination and right ascension depends on the situation of the planet in the zodiac. The aberration in longitude, being equal to the geocentric motion, will be more or less, according as that motion may be. It will be least when the planet is stationary; and greatest in the superior planets, when they are in opposition; but in the inferior planets the aberration is greatest at the time of their superior conjunction. AberrAtion, in optics, a deviation of the rays of light, when reflected, whereby they are prevented from meeting in the same point. Aberrations are of two kinds; one arising from the figure of the reflecting body, the other from the different refrangibility of the rays themselves: this last is called the Newtonian aberration, from the name of the discoverer. ABETTOR, or ABBETTor, in law, the person who promotes or procures a crime to be committed: thus, an abettor of murder is one who commands or counsels another to commit it. An abettor, according as he is present or absent at the time of committing the fact, is punishable as a principal or accessary. See Access Ary. An abettor is the same with one who is deemed art and part, by the law of Scotland. ABEYANCE, in law, is that which is in expectation, remembrance, and intendment of law. By a principle of law, in every land there is a fee simple in somebody, or it is in abeyance; that is, though at present it be in no man, yet it is, in expectancy, belonging to him that is next to enjoy the land. Where no person is seen or known, in whom the inheritance can vest, it may be in abeyance, as in limitation to several persons, and the survivor, and the heirs of such survivor, because it is uncertain who will be the survivor, yet the freehold cannot, because there must be a tenant to the praecipe always. ABJURATION, in law, is used for renouncing, disclaiming, and denying the Pretender to have any manner of right to the throne of these kingdoms: and that upon oath, which is required to be taken upon divers pains and penalties by many statutes, particularly 1 W. and M. 13 W. III. 1 Anne, 1 Geo. I. ABOLITION, in law, denotes the repealing any law or statute, and prohibiting some custom, ceremony, &c. Sometimes also it signifies leave granted by the king,

or a judge, to a criminal accuser to forbear any farther prosecution. Abolition is also used by ancient civilians and lawyers, for desisting from, or annulling, a legal prosecution; for remitting the punishment of a crime; and for cancelling or discharging a public debt. ABOMASUS, Ahom Asum, or AbomAsius, in comparative anatomy, names used for the fourth stomach of ruminating beasts, or such as cliew the cud. These have four stomachs, the first of which is called venter; the second, reticulum ; the third, omasus; and the fourth, abomasus. This last is the place where the chyle is formed, and from which the food descends immediately into the intestines. ABORTION, in medicine, an untimely or premature birth of a foetus, otherwise called a miscarriage; but if this happen before the second month of pregnancy, it is only called a false conception. See MediciNr, Midwifery, &c. Abortion, in law, if caused by giving a potion to, or striking a pregnant woman, was murder, but now is said to be a great misprision only, and not murder, unless the child be born alive, and die thereof. ABOUT, in military affairs, a word to express the movement by which a body of troops changes its front, by facing according to any given word of command. ABRA, a silver coin of Poland, nearly equivalent to the English shilling. See Coin. ABREAST, a sea term, expressing the situation of two or more ships, that lie with their sides parallel to each other, and their heads advanced. When the line of battle at sea is formed abreast, the whole squadron advances uniformly. Abreast within the ship, denotes on a line with the beam, or by the side of any object aboard. ABRIDGMENT, in law, the shortening a count, or declaration: thus, in assize, a man is said to abridge his plaint, and a woman her demand in action of dower, if any land is put therein, which is not in the tenure of the defendant; for on a plea of non-tenure, in abatement of the writ, the plaintiff may leave out those lands, and pray that the tenant may answer to the remainder. The reason is, that these writs run in general, and therefore shall be good for the rest. ABROMA, in botany, a word signifying not fit for food, is used in opposition to Theobroma, as a genus of plants belonging to the natural order of Columniferae, and the eighteenth class of Polyadelphia Dode. candria. There are two species, viz. the

the maple-leaved abroma, which is a tree with a straight trunk, yielding a gum when cut, and filled with a white pith like the elder; it flowers from June to October, and its fruit ripens in September and October; it is a native of New South Wales and the

Philippine islands, was introduced into Kew.

gardens about 1770, and is a hot-house plant, requiring great heat, and much water:—and Wheler's Abroma, so called by Koenig, in compliment to Edward Wheler, Esq. of the Supreme Council in Bengal;

this is a shrub with a brown bark, a native

of the East Indies, and is not known in Europe. There is but one of the species known in Europe, which is propagated with us by cuttings. The plant requires a strong heat, and abundance of water. The seeds rarely arrive at a state fit for propagation. ABRUS, in botany, from a Greek word signifying soft or delicate, so called from the extreme tenderness of the leaves, is a genus of the natural order of Leguminosae, and the seventeenth class of Diadelphia Decandria. There is one species, viz. the Abrus precatorius. It grows naturally in both Indies, Guinea, and Egypt. It is a perennial plant, rising to the height of eight or ten feet. Its leaflets have the taste of liquorice, whence it is called, in the West Indies, Jamaica wild liquorice, and used for the same purpose. There are two varieties, one with a white, and the other with a yellow seed. The seeds are commonly strung, and worn as ornaments in the countries where the plant grows wild; and they are frequently brought to Europe from Guinea, and the East and West Indies, and wrought into various forms with other hard seeds and shells. They are also used for weighing precious commodities, and strung as beads for rosaries, whence the epithet precatorius. They are frequently thrown, with other West Indian seeds, on the coast of Scotland. This plant was cultivated by Bishop Compton, at Fulham, before 1680. It is propagated by seeds, sown on a good hot-bed in spring, and previously soaked for twelve or fourteen hours in water. When the plants are two inches, each of them should be transplanted into a separate pot of light earth, and plunged into hot-beds of tanner's bark, and shaded from the sun. They will flower the second year, and sometimes ripen their seeds in England. ABSCESS, in medicine and surgery, an inflammatory tumour, containing purulent matter. See SURGERY. ABSCISSE, in conic sections, the part of the diameter of a curve line, intercepted

between the vertex of that diameter and the point where any ordinate or semi-ordimate to that diameter falls. From this definition it is evident, that there are an infinite number of variable abscisses in the same curve, as well as an infinite number of ordinates. In the parabola, one ordinate has but one abscisse; in an ellipsis, it has two; in an hyperbola, consisting of two parts, it has also two; and in curves of the second and third order, it may have three and four. See Conic SECTIONs. ABSCISSION, in rhetoric, a figure of speech, whereby the speaker stops short in the middle of his discourse: e.g. one of her age and beauty, to be seen alone, at such an hour, with a man of his character. I need say no more. ABSINTHIUM. See ARTEMIS1A. ABSORBENTS, in the materia medica, such medicines as have the power of drying up redundant humours, whether applied to ulcers, or taken inwardly. See MATERIA MEDICA, and PHARMACY. Absorbent ressels, in anatomy, are those which take up any fluid from the surface of the body, or of any cavity in it, and carry it into the blood. They are denominated according to the liquids which they convey, as Lacteals, or Lymphatics; the former conveying chyle, a milky fluid, from the intestines, the latter lymph, a thin pellucid liquor, from the places whence they take their origin. The lymphatics also take up any fluids that are extravasated, and likewise substances rubbed on the skin, as mercury, and convey them into the circulation. ABSTRACT idea, among logicians, the idea of some general quality or property considered simply in itself, without any respect to a particular subject: thus, magnitude, equity, &c. are abstract ideas, when we consider them as detached from any particular body or person. Various controversies have been maintained respecting the existence of abstract ideas; but all these disputes seem to be merely verbal. It is certainly impossible to possess an idea of an animal which shall have no precise colour, figure, magnitude, or the like; but it is an useful artifice of the understanding to leave these out in our general reasonings. Thus it is that the a, b, c, &c. of the algebraists are usefully applied to denote numbers, though undoubtedly they are only

general signs.

ABUCCO, Abocco, or Abocchi, a weight used in the kingdom of Pegu. ABUNDANT numbers, those whose

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