their colours from all the tints of yellow to the most obscure russet. They often cover the whole hemisphere, and then exhibit the most brilliant appearance. Their motions at this time are most amazingly quick; and they astonish the spectator with the rapid change of their form. They break out in places where none were seen before, skimming briskly along the heavens, are suddenly extinguished, and are succeeded by an uniform dusky tract. This again is brilliantly illuminated iu the same manner, and as suddenly left a dark space. In some nights, they assume the appearance of large columns, on one side of the deepest yellow, and on the other, gradually changing till it becomes undistinguished from the sky. They have generally a strong tremulous motion from one end to the other, and this continues till the whole vanishes. As for us, who see only the extremities of these northern phenomena, we can have but a faint idea of their splendour, and motions. According to the state of the atmosphere, they differ in colour; and sometimes assuming the colour of blood, they make a dreadful appearance. The rustic sages who observe them, become prophetic, and terrify the spectators with alarms of war, pestilence, and famine: nor, indeed, were these superstitious presages peculiar to the northern islands: appearances of a similar nature are of ancient date; and they were distinguished by the appellations of "phasmata," trabes," and "bolides," according to their forms and colours. In old times they were either more rare, or less frequently noticed: but when they occurred, they were supposed to portend great events, and the timid imagination formed of them aerial conflicts.

66

In the northern latitudes of Sweden and Lapland, the aurora borealis are not only singularly beautiful in their appearance, but afford travellers, by their almost constant effulgence, a very beautiful light during the whole night. In Hudson's bay, the aurora borealis diffuses a variegated splendour, which is said to equal that of the full moon. In the north-eastern parts of Siberia, according to the description of Gmelin, these northern lights are observed to "begin with single bright pillars, rising in the north, and almost at the same time in the north-east, which gradually increasing, comprehend a large space of the heavens, rush about from place to place with incredible velocity, and finally, almost cover the whole sky up to the zenith, and produce an ap

pearance as if a vast tent was expanded in the heavens, glittering with gold, rubies, and sapphire. A more beautiful spectacle cannot be painted; but whoever should see such a northern light for the first time, could not behold it without terroar. For however fine the illumination may be, it is attended, as I have learned from the relation of many persons, with such a hissing, cracking, and rushing noise through the air, as if the largest fire-works were playing off. To describe what they then hear, they make use of the expression 'spolochi chodjat,' that is, the raging host is passing.' The hunters, who pursue the white and blue foxes in the confines of the Icy sea, are often overtaken in their course by these northern lights. Their dogs are then so much frightened, that they will not move, but lie obstinately on the ground, till the noise has passed. Commonly, clear and calm weather follows this kind of northern lights. I have heard this account, not from one person only, but confirmed by the uniform testimony of many, who have spent part of several years in these very northern regions, and inhabited different countries from the Yenisei to the Lena; so that no doubt of its truth can remain. This seems indeed to be the real birth place of the aurora borealis."

This account of the noises attending the aurora borealis, allowing for some degree of exaggeration, has been corroborated by other testimonies. A person, who resided seven years at Hudson's Bay, confirms M. Gmelin's relation of the fine appearance and brilliant colours of the northern lights, and particularly of their rushing noise, which he affirms he has frequently heard, and compares it to the sound produced by whirling round a stick swiftly at the end of a string. A similar noise has also been heard in Sweden. Mr. Nairne also, being in Northampton at a time when the northern lights were remarkably bright, is confident he perceived a hissing, or whizzing sound. Mr. Belknap, of Dover, in New Hampshire, North America, testifies to this fact. M. Cavallo says, that the crackling noise is distinctly audible, and that he has heard it more than once. Similar lights, called auroræ australes, have been long since observed towards the south pole, and their existence has been more lately ascertained by Mr. Forster, who assures us that in his voyage round the world with Captain Cooke, he observed them in high southern latitudes, though attended with phenomena some

what different from those which are seen here. On February 17, 1773, in south latitude 58°, "a beautiful phenomenon (he says) was observed during the preceding night, which appeared again this and several following nights. It consisted of long columns of a clear white light, shooting up from the horizon to the eastward, almost to the zenith, and gradually spreading on the whole southern part of the sky. These columns were sometimes bent sideways at their upper extremities; and though in most respects similar to the northern lights (aurora borealis) of our hemisphere, yet differed from them in being always of a whitish colour, whereas ours assume various tints, especially those of a fiery and purpie hue. The sky was generally clear when they appeared, and the air sharp and cold, the thermometer standing at the freezing point."

In

The periods of the appearance of these northern lights are very inconstant. some years they occur very frequently, and in others they are more rare; and it has been observed that they are more common about the time of the equinoxes than at other seasons of the year. Dr. Halley (see Philos. Trans. No. 347, p. 406,) has collected together several observations, which form a kind of history of this phenomenon. After having particularly described the various circumstances which attended that observed by himself and many others in March, 1716, and which was singularly brilliant, he proceeds with informing us, that the first account of similar phenomena recorded in the English annals, is that of the appearance which was noticed January 30, 1560, and called "burning spears," by the author of a book intitled "A Description of Meteors," by W. F. D. D. reprinted at London, in 1654. The next appearance of a like kind, recorded by Stow, occurred on October 7, 1564. In 1574, as Camden and Stow inform us, an aurora borealis was seen for two successive nights, viz. 14th and 15th of November, with appearances similar to those observed in 1716, and which are now commonly noticed. The same phenomenon was twice seen in Brabant, in 1575, viz. on the 13th of February and the 28th of September; and the circumstances attending it were described by Cornelius Gemma, who compares them to spears, fortified cities, and armies fighting in the air. In the year 1580, M. Mastline observed these plasmata, as he calls them, at Baknang, in the county of Wirtemberg, in Ger

many, no less than seven times in the space of twelve months; and again at several different times, in 1581. On September 2nd, 1621, the same phenomenon was seen over all France; and it was particularly described by Gassendes, in his "Physics," who gave it the name of "aurora borealis." Another was seen all over Germany in November 1623, and was described by Kepler. Since that time, for more than eighty years, we have no account of any such phenomenon, either at home or abroad. In 1707, Mr. Neve observed one of small continuance in Ireland; and in the same year, a similar appearance was seen by Romer, at Copenhagen; and during an interval of eighteen months, in the years 1707 and 1708, this sort of light had been seen no less than five times. Hence it should seem, says Dr. Halley, that the air, or earth, or both, are not at all times disposed to produce this phenomenon, though it is possible it may happen in the day time, in bright moon shine, or in cloudy weather, and so pass unobserved. Dr. Halley further observes, that the aurora borealis of 1716, which he described, was visible from the west of Ireland to the confines of Russia, and to the east of Poland; extending at least near 30° of longitude, and from about the 50th degree of north latitude, over almost all the north of Europe; and in all places at the same time, it exhibited appearances similar to those which he observed at London. He regrets, however, that he was unable to determine its height for want of contemporary observations at different places.

and

Father Boscovich has determined the height of an aurora borealis, observed on the 16th of December 1737, by the Marquis of Poleni, to have been 825 miles; Mr. Bergman, from a mean of thirty computations, makes the average height of the aurora borealis to be 72 Swedish, or (supposing a Swedish mile to be about 64 English miles) 468 English miles. Euler supposes the height to be several thousands of miles; and Mairan also assigns to these phenomena a very elevated region, the far greater number of them being, according to him, about 200 leagues above the surface of the earth. Dr. Blagden, speaking of the height of some fiery meteors (Phil. Trans. vol. lxxiv. p. 227), says, that "the aurora borealis appears to occupy as high, if not a higher region, above the surface of the earth, as may be judged from the very distant countries to which it has been visi

ble at the same time;" he adds, that "the great accumulation of electric matter seems to lie beyond the verge of our atmosphere, as estimated by the cessation of twilight." However the height of these meteors, none of which appear to have ascended so high as 100 miles, is trivial, compared with the elevations above ascribed to the aurora borealis. But as it is difficult to make such observations on this phenomenon, as are sufficient to afford a just estimate of its altitude, they must be subject to considerable variation, and to material error.

It is not improbable, that the highest regions of the aurora borealis are the same with those in which fire-balls move; more especially as Dr. Blagden informs us, that instances are recorded, in which the northern lights have been seen to join, and form luminous balls, darting, about with great velocity, and even leaving a train behind like the common fire-balls. This ingenious author, however, conjecturing that distinct regions are allotted to the electrical phenomena of our atmosphere, assigns the appearance of tire-balls to that region which lies beyond the limits of our crepuscular atmosphere; and a greater elevation above the earth to that accumulation of electricity in a lighter and less condensed form, which produces the wonderfully diversified streams and coruscations of the aurora borealis,

AUSTRAL, something relating to the south: thus the six signs on the south side of the equinoctial are called austral signs.

AUTER fois acquit, in law, a plea made by a criminal that he has been already acquitted of the same crime, with which he is charged. There are likewise pleas of auter fois convict and attaint, that he has been before convicted of the same felony.

AUTHENTIC, something of acknowledged and received authority. In law it signifies something clothed in all its formalities, and attested by persons to whom credit has been regularly given. Thus, we say, authentic papers, authentic instruments. In music, authentic is a term applied to four of the church modes or tones, which rise a fourth above their dominants, which are always a fifth above their finals; in this distinguished from the plegal modes, which fall a fourth below their finals. Thus when an octave is divided arithmetically according to the numbers 2, 3, 4, that is, when the fifth is flat, and the fourth sharp, the mode or tone is called authentic, in -contradistinction to the plegal tone, where

the octave is divided harmonically by the numbers 3, 4, 6, which makes the fourth flat, and the fifth a sharp.

AUTHORITY, in a general sense, sig, nifies a right to command, and make one's self obeyed.

AUTHORITY, in law, signifies a power given by word, or writing, to a second person to act something, and may be by writ, warrant, commission, letter of attorney, &c. and sometimes by law. An authority given to another, to do what a person him, self cannot do is void; and it must be for doing a thing that is lawful, otherwise it will be no good authority.

Authority is represented in painting, like a grave matron sitting in a chair of state, richly clothed in a garment embroidered with gold, holding in her right hand a sword, and in her left a sceptre. By her side is a double trophy of books and arms.

AUTOGRAPHUM, the very hand writing of a person, or the original manuscript of a treatise or discourse. Autographa, or original manuscripts of the New Testament, are the copies written by the apostles, or by amanuenses under their immediate inspection. St. Paul seems generally to have adopted the latter mode; but to prevent the circulation of spurious epistles, he wrote the concluding benediction with his own hand. The early loss of the autographa of the New Testament affords matter of surprise, when it is known that the original manuscripts of Luther, and other eminent men who lived at the time of the reformation are still subsisting.

AUTOMATUM, or AUTOMATON, an instrument, or rather machine; which, by means of springs, weights, &c. seems to move itself, as a watch, clock, &c. Such also were Archytus's flying dove, Regiomontanus's wooden-eagle, &c. See AN

DROIDES.

AUTUMN, the third season of the year, when the harvest and fruits are gathered in. Hence, in the language of the Alchemists, it signifies the time when the philosophers' stone is brought to perfection.

Autumn is represented, in painting, by a man at perfect age, clothed like the vernal, and likewise girded with a starry girdle; holding in one hand a pair of scales equally poized, with a globe in each; in the other, a bunch of divers fruits and grapes. His age denotes the perfection of this season, and the balance, that sign of the zodiac which the sun enters when our autumn

begins.

AUTUMNAL signs, in astronomy, are the signs Libra, Scorpio, and Sagittarius, through which the sun passes during the autumn.

AUXILIARY verbs, in grammar, are such as help to form or conjugate others; ́that is, are prefixed to them, to form or denote the moods or tenses thereof. As to have and to be, in the English; estre et avoir in the French; ho et sono in the Italian, &c. In the English language, the auxillary verb am, supplies the want of passive verbs.

AUXILIARY, in military affairs: by this term is understood foreign or subsidiary troops, which are furnished to a belligerent power in consequence of a treaty of alliance, or for pecuniary considerations. Of the latter description may be considered the Swiss soldiers, who formerly served in France, and the Hessians who were employed by Great Britain, during a patt of the American war, and on other occasions.

AUXILIUM curia, in law, a precept or order of court, to cite, or convene one party at the suit of another.

AUXILIUM ad filium militem faciendum, vel filiam maritandam, a precept or writ directed to the sheriff of every county where the king or other lords had any tenants, to levy of them reasonable aid, towards the knighting his eldest son, or the marriage of his eldest daughter.

AWAIT, in law, way-laying, or layingin-wait to execute some mischief. It is enacted, that no charter of pardon shall be allowed before any justice, for the death of a man slain by await or malice prepence. 13 Rich. II.

AWARD, in law, the judgment of an arbitrator, or of one who is not appointed by the law a judge, but chosen by the parties themselves for terminating their differSee ARBITRator.

ence.

AWL, or AUL, among shoemakers, an instrument wherewith holes are bored through the leather, to facilitate the stitching or sewing the same. The blade of the awl is usually a little flat and bended, and the point ground to an acute angle.

AWME, or AUME, a Dutch liquid measure, containing eight steckans, or twenty verges or verteels, equal to the tierce in England, or to one-sixth of a ton of

France.

AWN. See ARISTA.

AWNING, in the sea-language, is the hanging a sail, tarpanling, or the like, over any part of the ship, to keep off the sun,

rain, or wind. That part of the poop-deck which is continued forward beyond the bulk-head of the cabin, is also called the awning.

AXETONE. See NEPHRite.

AXILLA, in anatomy, the arm-pit, or the cavity under the upper part of the arm.

AXILLA, in botany, the space compre. hended betwixt the stems of plants and their leaves.

AXIOM, in philosophy, is such a plain, self-evident, and received notion, that it cannot be made more plain and evident by demonstration; because it is itself better known than any thing that can be brought to prove it: as, that nothing can act where it is not; that a thing cannot be, and not be, at the same time; that the whole is greater than a part thereof; and that from nothing, nothing can arise. By axioms, called also maxims, are understood all common notions of the mind, whose evidence is so clear and forcible, that a man cannot deny them, without renouncing common sense and natural reason.

The rule whereby to know an axiom, is this: whatever proposition expresses the immediate clear comparison of two ideas, without the help of a third, is an axiom. But if the truth does not appear from the immediate comparison of two ideas, it is no axiom.

These sort of propositions, under the name of axioms, have, on account of their being self-evident, passed not only for principles of science, but have been supposed innate, and thought to be the foundation of all our other knowledge; though, in truth, they are no more than identic propositions : for to say that all right angles are equal to each other, is no more than saying, that all right angles are right angles, such equality being implied in the very definition. All considerations of these maxims, therefore, can add nothing to the evidence or certainty of our knowledge of them: and how little they influence the rest of our knowledge, how far they are from being the foundation of it, as well as of the truths first known to the mind, Mr. Locke, and some others, have undeniably proved. According to Bacon, it is impossible that axioms raised by argumentation should be useful in discovering new works; because the subtilty of nature far exceeds the subtilty of arguments: but axioms, duly and methodically drawn from particulars, will again easily point our new particulars, and so render the sciences active,

The axioms in use being derived from slender experience, and a few obvious particulars, are generally applied in a corresponding manner. No wonder, therefore, they lead us to few particulars; and if any instance, unobserved before, happen to turn up, the axiom is preserved by some trifling distinction, where it ought rather to be corrected.

AXIOM is also an established principle in some art or science.

Thus it is an established axiom in physics, that nature does nothing in vain; so it is in geometry, that if to equal things you add equals, the sums will be equal. It is an axiom in optics, that the angle of incidence is equal to the angle of reflection, &c. In which sense too, the general laws of motion are called axioms: whence it may be observed, that these particular axioms are but deductions from certain hypotheses.

AXIS, in geometry, the straight line in a plane figure, about which it revolves, to produce or generate a solid: thus, if a semicircle be moved round its diameter at rest, it will generate a sphere, the axis of which is that diameter.

Axis, in astronomy. 1. Axis of the world, an imaginary right line conceived to pass through the centre of the earth, from one pole to the other, about which the sphere of the world in the Ptolemaic system revolves in its diurnal rotation. 2. The axis of a planet, is that line drawn through the centre about which the planet revolves. The sun, together with all planets, except Mercury, Saturn, and Herschel, are known by observation to move about their respective axis. The axis of the earth, during its revolution round the sun, remains parallel to itself, and is inclined to the plane of the ecliptic, making with it an angle of 661⁄2 degrees. 3. The axis of the equator, horizon, ecliptic, zodiac, &c. are right lines drawn through the centers of those circles perpendicular to their planes.

Axis, in conic sections, a right line dividing the section into two equal parts, and cutting all its ordinates at right angles. See CONIC SECTIONS.

Axis, in mechanics. The axis of a ballance is that line about which it moves, or rather turns about. Axis of oscillation is a right line parallel to the horizon, passing through the centre about which a pendulum vibrates.

Axis in peritrochio, one of the five mechanical powers, consisting of a peritrochium or wheel concentric with the base of

a cylinder, and moveable together with it about its axis. See MECHANICS.

Axis, in optics, is that ray, among all others that are sent to the eye, which falls perpendicularly upon it, and which consequently passes through the centre of the eye.

Axis of a glass or lens, is a right line joining the middle points of the two opposite surfaces of the glass.

AXIS of incidence, in dioptrics, is a right line perpendicular in the point of incidence, to the refracting superficies, drawn in the same medium that the ray of incidence comes from.

Axis of refraction is a right line drawn through the refracting medium, from the point of refraction, perpendicular to the refracting superficies.

AXYRIS, in botany, a genus of the Monoecia Triandria class of plants, in the male flowers of which the calyx is a perianthium composed of four patent, obtuse leaves, divided into three segments: there is no corolla: in the female flowers the calyx is composed of five obtuse, concave, connivent, and permanent leaves, with the two exterior ones shorter than the rest; there is no corolla; nor is there any pericarpium; the seed is single, oblong, compressed obtuse, and contained in the cup.

AYE-aye, in natural history, a singular quadruped discovered by Sonnerat, in the island of Madagascar, and described in his voyage to the East Indies. Sonnini forms a new genus of this animal, under the name of "Chieromys," but Gmelin ranks it under the genus 66 Sciuras," which see.

AYENIA, in botany, so called in honour of the Duke d'Ayen, a great promoter of the science of botany, of the Gynandria Pentandria class and order. Natural order of Columniferæ. Malvacea Jussica. Essential character, monogynous. Calyx fiveleaved. Petals united into a star, with long claws; five anthers, under the star; capsule five-celled. There are four species; of which, three are natives of South America, and one of Jamaica. These plants are propagated by seeds, sown in the spring in hotbeds, where they must continue; but they will want a good portion of free air. If exposed to the open atmosphere, they will not thrive; and if too much drawn, they do not flower well. The plant will live through the winter, but as they perfect their seeds the first year, the old plants are seldom continued.

AZALEA, in botany, of the Pentandria