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CHRONOUS, is applied to such vibrations of a pendulum as are performed in the same space of time, as all the vibrations or swings of the same pendulum are, whether the arches it describes be longer or shorter: for when it describes a shorter arch it moves so much the slower, and when a long one proportionably faster.

ISOCHRONAL line, that in which a heavy body is supposed to descend without any acceleration.

M. Leib. z shows, that an heavy body, with a degree of velocity acquired by the descent from any height, may descend from the same point by an infinite number of isochronal curves, all which are of the same species, differing from one another only in the magnitude of their parameters; such are all the quadrato-cubical paroboloids, and consequently similar to one another. He shows also there, how to find a line in which a heavy body descending shall recede uniformly from a given point, or approach uniformly to it.

ISOETES, in botany, a genus of the Cryptogamia Filices class and order. Natural order of Filices, or Ferns. Essential character: male, anther within the base of the frond: female, capsule two-celled, within the base of the frond. There are two

species, viz. I. lacustris, common quillwort, and I. coromandelina, Coromandel quillwort, both natives of mountain lakes, and in wet places that are inundated in the rainy season.

ISOPERIMETRICAL figures, in geometry, are such as have equal perimeters, or circumferences.

Isoperimetrical lines and figures have greatly engaged the attention of mathematicians at all times. The fifth book of Pappus's Collections is chiefly upon this subject; where a great variety of curions and important properties are demonstrated, both of planes and solids, some of which

were then old in his time, and many new ones of his own. Indeed, it seems, he has

here brought together into this book all the properties relating to isoperimetrical figures then known, and their different degrees of capacity. The analysis of the general problem concerning figures, that, among all those of the same perimeter, produce maxima and minima, was given by Mr. James Bernoulli, from computations that involve the second and third fluxions. And several enquiries of this nature have been since prosecuted in like manner, but not always with equal success. Mr. Maclaurin, to vin

dicate the doctrine of fluxions from the imputation of uncertainty or obscurity, has illustrated this subject, which is considered as one of the most abstruse parts of this doctrine, by giving the resolution and composition of these problems by first fluxions only; and in a manner that suggests a synthetic demonstration, serving to verify the solution. See Maclaurin's Fluxions. Mr. Crane also, in the Berlin Memoirs for 1752, has given a paper in which he proposes to demonstrate, in general, what can be demonstrated only of regular figures in the elements of geometry, viz. that the circle is the greatest of all isoperimetrical figures, regular or irregular. We shall now mention a few of the properties of isoperimetrical figures.

1. Of isoperimetrical figures, that is the greatest that contains the greatest number of sides, or the most angles, and consequently a circle is the greatest of all figures that have the same ambit as it has.

2. Of two isoperimetrical triangles, hav ing the same base, whereof two sides of one are equal, and of the other unequal, that is the greater whose two sides are equal.

3. Of isoperimetrical figures, whose sides are equal in number, that is the greatest which is equilateral and equiangular. From hence follows that common problem of making the hedging or walling that will wall in one acre, or even any determinate number of acres, a; fence or wall in any greater number of acres whatever, b. In order to the solution of this problem, let the greater number, b, be supposed a square; let x be one side of an oblong, whose area is a; then will be the other

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side; and 2 - + 2 x will be the ambit of the oblong, which must be equal to four times

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xx−dx+jdd=−2+dd tandria Monogynia class and order. NatuITEA, in botany, a genus of the Pen

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Thus if one side of the square be 10; and one side of an oblong be 19, and the other 1; then will the ambits of that square and oblong be equal, viz. each 40, and yet the area of the square will be 100, and of the oblong but 19.

ISOPYRUM, in botany, a genus of the Polyandria Polygynia class and order. Natural order of Multisilique. Ranunculacea, Jussien. Essential character: calyx none; petals five; nectary trifid, tubular; capsule recurved, many-seeded. There are three species.

ISOSCELES triangle, in geometry, one that has two equal sides. See GEOMETRY. ISSUE, in law, has many significations, sometimes being used for the children be gotten between a man and his wife; some times for profit growing from amerce, ments or fines; and sometimes for profits of lands or tenements; sometimes for that point of matter depending in a suit, when, in the course of pleading, the parties in the case affirm a thing on one side, and deny it on the other, they are then said to be at issue; all their debates being at last contracted into a single point, which may be determined either in favour of the plaintiff or defendant.

ISSUES, in surgery, are little ulcers made designedly by the surgeon in various parts of the body, and kept open by the patient for the preservation or recovery of his health.

ITCH, a cutaneous disease, supposed to be caused by an insect, a species of the genus Acarus, viz. A. scabiei, which, when viewed by a good microscope, is white with reddish legs; the four hind ones having a long bristle. It is found in the small pellucid vesicles with which the hands and joints of persons infected with the itch are covered. It appears to be not only the cause of the disorder, but the reason why it is so highly infectious.

ITCHING, an uneasy sensation, which occasions a desire of scratching the place affected. It is frequently a troublesome sensation, but more nearly allied to pleasure than pain. As pain is supposed to proceed from too great an irritation, so does itching proceed from a slight one. Certain species of itching excites people to many necessary actions, as the excretion of the feces and urine; coughing, sneezing, &c.

ral order of Rhododendra, Jussien. Essential character: capsule two-celled, twovalved, many-seeded; stigma emarginate. There are two species, viz. I. virginica. Virginian itea; and I. cyrilla, entire-leaved itea. These are both shrubs. Linnæus remarks, that the itea virginica has the appearance of the Padus; that the leaves are petioled and the flowers in terminating racemes. The stigma is headed in this species, whereas in the other it is bifid or double; the former is a native of North America; the latter of Carolina and Jamaica.

ITTRIA. This earth was discovered by Gadolin, a Swedish chemist, in a fossil, found at Ytterby, in Sweden, which has since received the name of gadolinite, and in which it is combined with silex and lime. The discovery was confirmed by Ekeberg, Klaproth, and Vauquelin; and the same earth has been discovered in some other fossils particularly combined with lantalium. In several of its properties ittria resembles giucine, particularly in forming salts of a sweet taste, and in being soluble in carbonate of ammonia; but it differs entirely in others.

The process followed by Vauquelin to obtain this earth from the gadolinite was to dissolve it, with the assistance of heat, in diluted nitric acid, pouring off the solution. from the undissolved silex. The liquor is then evaporated to dryness by which any remaining silex and any oxide of iron is separated from combination with the acid. By redissolving the residuum in water, the compound of nitric acid and ittria is obtained: if there are any traces of iron, the liquor is either again evaporated to dryness or a little ammonia is added; and after the separation of the oxide or iron by yellow flakes, the solution is decomposed by ammonia, which precipitates the new earth. (Philosophical Magazine, vol. viii. p. 369.) The process employed by Klaproth is similar; nitro-muriatic acid being employed; the iron being removed by the action of succinate of soda; and the ittria being precipitated by carbonate of soda. (Analytical Essays, vol. ii. p. 47.)

Ittria is obtained in the form of a white powder, and is heavier than any other earth; its specific gravity according to Ekeberg being 4.842. It is not fusible alone, but with borax it forms a white glass.

It is not soluble in water, but it retains conchoidal; its hardness is such that it is that fluid with considerable force.

Ittria combines with the acids; its salts, as has been remarked, having generally a sweetish taste. Several of them, too, are coloured, a property in which it differs from all the other earths.

The sulphate of ittria crystallizes in small brilliant grains, according to Klaproth, of a rhomboidal form, and of a colour inclining to an amethyst red. Their taste is sweet, becoming also astringent. They require from twenty-five to thirty parts of water, and are not more soluble in hot water. Their specific gravity is 2.79. The sulphuric acid is expelled by a red heat. Nitrate of ittria can scarcely be crystallized; it assumes a gelatinous consistence by evaporation, and becomes brittle when this jelly cools. Its taste is similar to that of the sulphate. The muriate is obtained nearly in the same form. The phosphate formed by complex affinity is insoluble. The acetite is a crystallizable salt of a pale red colour.

The salts of ittria are decomposed by the three alkalies, and by lime, astrontites, and barytes.

Ittria is not dissolved by the liquid alkalies, nor do they redissolve it when added in excess, after having precipitated it from its solutions. This affords a distinguishing character between it and glucine. It is soluble in the alkaline carbonates, particularly in the carbonate of ammonia.

Prussiate of potash throws down from its solution a granular precipitate, of a white or pearl-grey colour. It is also precipitated in grey flocculi by the watery or spirituous infusion of galls; but very slightly by the pure gallic acid. It is not affected by sul phuretted hydrogen, or hydro-sulphuret of ammonia added to its solutions.

The great specific gravity of this earth, its forming coloured salts, and being precipitated by the alkaline prussiates, and by tannin, from its solutions, in some measure connect it with the metals, and lead to the suspicion that it may be a metallic oxide.

The gadolinite is the only fossil that can be considered as belonging to the genus of which this earth is the base, for the yttrotantalite contains it iu small quantity only, and is properly a metallic fossil belonging to the genus Tantalium. The gadolinite occurs massive, and disseminated its colour; is a deep greenish black. Its internal lustre is resplendent; it is opaque; its fracture is

not scratched by the knife; its specific gravity is 4.2. It intumesces before the blow-pipe, but is not fused. With nitric acid it forms a gelatinous solution. Accord ing to Klaproth it consists of ittria 59.75, silex 21.25, oxide of iron 17.5, argil 0.5, water 0.5. The analysis of it by Ekeberg and Vauquelin give the proportion of ittria rather less, and of silex and iron somewhat

more.

IVA, in botany, a genus of the Monoecia Pentandria class and order. Natural order of Compositæ Nucamentaceæ. Corymbiferæ, Jussieu. Essential character: male, calyx common, three-leaved; corolla of the disk, one-petalled, five-cleft; receptacle with hairs or linear chaffs: female, in the ray, five, or fewer; corolla none; styles two, long; seeds naked, blunt. There are two species, viz. I. annua, annual iva; and I. frutescens, shrubby iva, or bastard Jesuits' bark tree.

JUBILEE, a time of public and solemn festivity among the ancient Hebrews. This was kept every fiftieth year: it began about the autumnal equinox, and was proclaimed by sound of trumpet throughout all the country. At this time all slaves were released, all debts annihilated, and all lands, houses, wives, and children, however alienated, were restored to their first owners. During this whole year all kind of agriculture was forbidden, and the poor had the benefit of the barvest, vintage, and other productions of the earth, in the same man. ner as in the sabbatic, or seventh year. As this was designed to put the Israelites in mind of their Egyptian servitude, and to prevent their imposing the like upon their brethren, it was not observed by the gentile proselytes.

The Christians, in imitation of the Jews, have likewise established jubilees, which began in the time of Pope Boniface VIII. in the year 1300, and are now practised every twenty-five years; but these relate only to the pretended forgiveness of sins, and the indulgencies granted by the church of Rome.

JUDGE. The judges are the Chief magistrates in the law, to try civil and criminal causes. Of these there are twelve in England, viz. the Lord's Chief Justices of the Courts of King's Bench and Common Pleas ; the Lord Chief Baron of the Exchequer; the three puisne or inferior judges of the two former courts, and the three puisne barons of the latter. By statute 1 Geo. III,

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c. 25, the judges are to continue in their offices during their good behaviour, notwithstanding any demise of the crown (which was formerly held immediately, to vacate their seats) and their full salaries are absolutely secured to them during the continuance of their commissions, by which means the judges are rendered completely independent of the king, his ministers, or his successors. A judge at his creation takes an oath that he will serve the king, and indifferently administer justice to all men, without respect of persons, take no bribe, give no counsel where he is a party, nor deny right to any, though the king or any other, by letters, or by expressed words, command the contrary, &c. and in default of duty, to be ans verable to the king in body, land, and goods. Where a judge has an interest, neither he nor his deputy can determine a cause, or sit in court, and if he do, a prohibition lies.

Judges are punishable for wilful offences againt the duty of their situations; instances of which happily live only in remembrance. A judge is not answerable to the king, or the party, for mistakes or errors in his judgment, in a matter of which he has jurisdic

tion.

JUDGMENT, among logicians, a faculty or rather act of the hunran soul, whereby it compares its ideas, and perceives their agreement or disagreement.

JUDGMENT. The opinion of the judges is so called, and is the very voice and final doom of the law; and, therefore, is always taken for unquestionable truth'; or it is the sentence of the law pronounced by the court upon the matter contained in the record. Judgments are of four sorts, viz. 1. Where the facts are confessed by the parties, and the law determined by the court, which is termed judgment by demurrer. 2. Where the law is admitted by the parties, and the facts only are disputed, as in judgment upon a demurrer. 3. Where both the fact and the law arising thereon are admitted by the defendant, as in case of judgment by confession or default. 4. Where the plaintiff is convinced that fact or law, or both, are insufficient to support his action, and therefore abandons or withdraws his prosecution, as in case of judgment upon a nonsuit or retraxit. See WARRANT of ATTORNEY.

Judgments are either interlocutory or final. Interlocutory judgments are such as are given in the middle of a cause, upon some plea, proceeding, or default, which is

only intermediate, and doth not finally determine or complete the suit; as upon dilatory pleas, when the judgment in many cases is that the defendant shall answer over, that is, put in a more substantial plea. Final judgments are such as at once put an end to the action, by declaring that the plaintiff hath either entitled himself, or hath not, to recover the remedy he sues for.

JUGLANS, in botany, walnut tree, a genus of the Monoecia Polyandria class and order. Natural order of Amentaceæ. Terebintaceæ, Jussieu. Essential character: male, calyx one-leafed, scale-form; corolla six-parted; filaments eighteen: female, calyx four-cleft, superior; corolla four-parted; styles two; drupe with a grooved nucleus. There are eight species, of which J. regia, common walnut, is a very large and lofty tree, with strong spreading boughs. There are several varieties, but they all vary again when raised from the seed, and nuts from the same tree will produce different fruit : persons, therefore, who plant the walnut for its fruit should make choice of the trees in the nurseries when they have their fruit upon them. In France, Switzerland, &c. the wood is in great request for furniture, as it was formerly in England, till the use of mahogany superseded it; it is in great repute with the joiner, for the best grained and coloured wainscot; with the gun-smith, for stocks; with the coach-maker, for wheels and the bodies of coaches; with the cabinetmaker, for inlayings, especially the firm and close timber about the root, which is admirable for flecked and cambleted works. To render this wood the better coloured, joiners put the boards into an oven after the batch is out, or lay them in a warm stable; and when they work it, polish it over with its own oil very hot, which makes it look black and sleek, and the older it is the more estimable. The husks and leaves being macerated in warm water, and the liquor poured on grass walks and bowlinggreens will infallibly kill the worms, without endangering the grass. Not that there is any thing peculiarly noxions in this decoction; but worms cannot bear the application of any thing bitter to their bodies, which is the reason that bitters, such as gentian, are the best destroyers of worms lodged in the bodies of animals.

JUGULAR, in anatomy, an appellation given to two veins of the neck, which arise from the subclavians. See ANATOMY.

JUGULARES, in natural history, an order of fishes according to the Linnæan

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NOLOGY.

This period was called the Julian, not because invented by Julius Cæsar; since the Julian epocha was not received till the year 4669, but because the system consists of Julian years. This epocha is not historical but artificial, being invented only for the use of true epochas; for Scaliger considering that the calculation was very intricate in using the years of the creation, the years before Christ, or any other epocha whatever, in regard that another person could not understand what year this or that writer meant; to remove such doubts in the computation of time, he thought of this period: which commencing 710 years before the beginning of the world, the various opinions concerning other epochas may commodiously be referred to it. See EPOCHA.

The most remarkable uses of the Julian period are as follow: 1. That we can explain our mind to one another, for every year in this period has its peculiar cycles, which no other year in the whole period has; whereas, on the contrary, if we reckon by the years of the world, we must first enquire how many years any other reckons from the creation to the year of Christ, which multiple-inquisition is troublesome and full of difficulties, according to the method of other periods. 2. That the three cycles of the sun, moou, and indiction, are easily found in this period. 3. That if it be known how the chronological characters are to be found in this period, and how the years of any other epocha are to be connected with the years of it, the same characters also may, with little labour, be applied to the years of all other epochas.

JULUS, in natural history, a genus of insects of the order Aptera. Lip crenate,

emarginate; antennæ moniliform; two feelers, filiform; body long, semi-cylindri cal, consisting of numerous transverse seg. ments; legs numerous, twice as many on each side as there are segments of the body. There are fourteen species, of which we shall notice the J. indus, or great Indian julus, which is six or seven inches long; found in the warmer parts of Asia and America, inhabiting woods and other retired places. It has 115 legs on each side, the body is ferruginous; legs yellow; the last segment of the body is pointed. The most common species is the J. sabulosus, about an inch and a quarter long; the colour brownish black, except the legs, which are pale or whitish; it is an oviparous animal; and the young when first hatched are small and white, and furnished with only three pair of legs, situated near the head, the remaining pairs, in all 120, do not make their appearance till some time after. This species inhabits Europe, and is found in damp places and in nuts. The juli tribe are nearly allied to the scolopendræ, or centipedes, but their body instead of being flattened, as in those insects, is nearly cylindrical, and every joint or segment is furnished with two pair of feet, the number on each side doubling that of the segments, but in the scolopendra the number of joints and of feet is equal on each side. The eyes of the juli are composed of hexagonal convexities, as in most of the insect tribe, and the mouth is furnished with a pair of denticulated jaws. When disturbed the juli roll themselves up into a flat spiral: their gene. ral motion is rather slow and undulatory.

JUNCUS, in botany, rush, a genus of the Hexandria Monogynia class and order. Natural order of Tripetaloideæ. Junci, Jussieu. Essential character: calyx six-leaved; corolla none; capsule one-celled. There are twenty-nine species. The rushes have a simple grassy stem, without leaves or knots, or else knotty, with a sheathing leaf at each knot; flowers terminating or lateral, corymbed or panicled, with the branch. lets spathaceous at the base.

These plants agree with the grasses in the glumes of their flowers, and the sheaths of their leaves; they differ in having the stems filled with pith, whereas in grasses it is hollow. The rushes form an intermediate link between the grasses and some of the liliaceous plants, as anthericum, &c.

They form naturally two divisions, one without leaves allied to scirpus, &c. and the other with leafy stems. But all classical

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