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air; all bodies, at least solid and liquid substances, are equally susceptible of it, and if it has ceased, from a reduction of temperature, it may be renewed by the temperature being again raised. The point of temperature at which the first stage of ignition takes place, or at which bodies arrive at a red heat, appears to be the same in all, and is supposed to be about 800° of Fahrenheit. By raising the temperature, the illumination becomes brighter, and the red light acquiresa mixture of yellow rays. At length, by still increasing it, we come to the white heat, which is the highest state of ignition. Aeriform fluids are not brought into a state of illumination by heat. The phenomena are produced not only by the application of heat, but likewise by friction and attrition. JIB, in naval affairs, the foremost sail of a ship, being a large stay-sail, extended from the outer end of the bowsprit, prolonged by the jib-boom, towards the foretop-mast-head. In cutters and sloops, the jib is on the bowsprit, and extends towards the lower mast-head. The jib is a sail of great command with any side wind, but especially when the ship is close-hauled, or has the wind upon her beam ; and its effort in turning her head to leeward is very powerful, and of great utility, particularly when the ship is working through a narrow channel. Jib-boom is a continuation of the bowsprit forward, being run out from the extremity in a similar manner to a top-mast on a lower-mast, and serving to extend the bottom of the jibs and the stay of the fore-top-gallant-mast. JIGGER, in naval affairs, a machine consisting of a piece of rope, five feet long, with a block at one end, and a sheave at the other, used to hold on the cable when it is heaved into the ship, by the revolution of the windlass. This is particularly useful, when either slippery with mud or ooze, or when it is stiff and unwieldy, in both which cases it is ve difficult to stretch it back from the windlass by hand, which, however, is done with facility and expedition by means of the jigger. ILEX, in botany, holly, a genus of the Tetrandria Tetragynia class and order.— Natural order of Dumosae. Rhamni, Jussieu. Essential character: calyx fourtoothed; corolla wheel-shaped ; style none; berry four-seeded. There are sixteen species. This genus consists of small trees or shrubs,with alternate leaves, evergreen, toothed, or thorny; and axil. lary, many-flowered peduncles. I. aqui

folium, common holly, is usually from twenty to thirty feet in height, though it sometimes exceeds sixty feet; the trunk is covered with a greyish bark, and those trees which are not lopped, or browzed by cattle, are commonly furnished with branches the greatest part of their length, forming a sort of cone. Mr. Millar says, the difference of sexes in the flowers of the holly was first observed by his father. In his garden at Streatham, in Surrey, he had many of these trees, which, before he had possession of the place, were shorn into round heads: he emancipated them from their slavery, pruned them, and trained up leading shoots. Seeming§ glad to be released from their shackles, they quickly rewarded him with this discovery concerning the nature of their flowers, which he communicated to the Royal Society. He perfectly recollects having carefully attended to the flowering of these trees during several seasons, and having uniformly observed hermaphrodite flowers on some, and male flowers on others: in the former, the anthers were different from those in the male flowers, and appeared to be effete, and there never was a single male flower mixed with the hermaphrodite, or a hermaphrodite with the males, or any flower except the two here described. The holly makes an impenetrable fence, and bears cropping well, nor is its verdure, or the beauty of its scarlet berries, ever observed to suffer from the severest of our winters. Mr. Evelyn's impregnable holly-hedge, four hundred feet in length, pine feet high, and five in diameter, has been much celebrated by himself, Ray, and others. The wood of this tree is the whitest of all hard woods, and used by the inlayer, especially under thin plates of ivory. The mill-wright, turner, and engraver, prefer it to any other: it also makes the best handles and stocks for tools, flails, the best riding rods, and carters’ whips; bowls, chivers, and pins for blocks; Mr. Millar says it is made into hones for setting razors; that the wood, taking a fine

polish, is proper for several kinds of fur

niture; that he has seen the floor of a room laid in compartments with this and mahogany, which had a very pretty ef. fect. It is much used with box, yew, and white thorn, in the small trinkets and other works, carried on in and about Tunbridge, commonly called Tunbridge Ware. Sheep and deer are fed during the winter with the croppings. Birds eat the berries. The bark fermented, and afterwards washed from the woody fibres, makes the common bird lime. Forty or fifty varieties depending on the variegations of the leaves or thorns, and the colour of the berries all derived from this one species, are raised by the nursery gardeners for sale, and were formerly in great esteem : but since the old taste of filling gardens with shorn evergreens has been laid aside, they are less regarded ; a few however of the most lively varieties have a good effect in the winter season. ILIUM, in anatomy, the third and last of the small intestines. See ANATomy. ILLECEBRUM, in botany, a genus of the Pentrandria Monogynia class and order. Natural order of Holoraceae. Amaranthi, Jussieu. Essential character: calyx five-leaved, cartilaginous; corolla none; stigma simple; capsules five valved, one seeded. There are twenty-one species, natives of North and South America and the West India Islands. ILLICIUM, in botany, a genus of the Polyandria Polygynia class and order. Natural order of Coadumatae. Magnoliae, Jussieu. Essential character: calyx sixleaved; petals twenty seven ; capsules several, disposed in a circle; bivalve, oneseeded. There are two species, viz. I. anisatum, yellow-flowered aniseed tree; and I. floridanum, red-flowered aniseed tree. Both these plants bear a great resemblance to each other. Thunberg doubts their being distinct species. The whole of the first mentioned plant, especially the fruit, has a pleasant aromatic smell, and a sweetish subacrid taste. In China it is in frequent use for seasoning dishes, especially such as are sweet. In Japan they place bundles and garlands of the aniseed tree in their temples before their idols, and on the tombs of their friends. They also use the powdered bark as incense to their idols. A branch put into the decoction of tetraodon hispidum is supposed to increase the virulence of the poison. The bark finely powdered is used by the public watchmen to make a chronometer, or instrument for measuring the hours, by slowly sparkling at certain spaces in a box, in order to direct when the public bells are to sound. ILLUMINATING, a kind of miniature ainting, anciently much practised for Hillustrating and adorning books. Besides the writers of books, there were artists,

whose profession was to ornament and paint manuscripts, who were called illuminators; the writers of books first finished their part, and the illuminators embellished them with ornamented letters and paintings. We frequently find blanks left in manuscripts for the illuminators, which were never filled up. Some of the ancient manuscripts are gilt and burnished in a style superior to later times. Their colours were excellent, and their skill in preparing them must have been very great The practice of introducing ornaments, drawings, emblematical figures, and even portraits, into manuscripts, is of great antiquity. Varro wrote the lives of 700 illustrious Romans, which he enriched with their portraits, as Pliny attests in his “Natural History.” Pomponius Atticus, the friend of Cicero, was the author of a work on the actions of the great men amongst the Romans, which he ornamented with their portraits, as appears in his life by Cornelius Nepos. But these works have not been transmitted to posterity. There are, however, many precious documents remaining, which exhibit the advancement and decline of the arts in different ages and countries. These inestimable paintings and illuminations display the manners, customs, habits, ecclesiastical, civil and military, weapons, and instruments of war, utensils and architecture of the ancients; they are of the greatest use in illustrating many important facts relative to the history of the times in which they were executed. In these treasures of antiquity are preserved a great number of specimens of Grecian and Roman art, which were executed before the arts and sciences fell into neglect and contempt. The manuscripts containing these specimens form a valuable part of the riches preserved in the principal libraries of Europe. The Royal, Cottonian, and the Harleian Libraries, as also those in the two universities in England, the Vatican at Rome, the Imperial at Vienna, the Royal at Paris, St. Mark's at Venice, and many others. A very ancient MS. of Genesis, which was in the Cottonian Library,and almost destroyed by a fire in 1731, contained 250 curious paintings in water colours. Twenty-one fragments, which escaped the fire, are engraven by the society of antiquarians of London. Without mentioning others, we may observe, that Mr. Strutt has given the public an opportunity of forming some judgment of the degree of delicacy and art with which these illuminations were executed, by publishing prints of a pro: digious number of them, in his “ Regal and Ecclesiastical Antiquities of England,” and “View of the Customs, &c. of England.” In the first of these works we are presented with the genuine portraits, in miniature, of all the kings, and several of the queens of England, from Euward the Confessor to Henry VII. mostly in their crowns and royal robes, together with the portraits of many other eminent persons of both sexes. The illuminators and painters of this period seem to have been in possession of a considerable number of colouring materials, and to have known the arts of preparing and mixing them, so as to form a great variety of colours: for in the specimens of their miniature paintings that are still extant, we perceive not only the five primary colours, but also various combinations of them. Though Mr. Strutt's prints do not exhibit the bright and vivid colours of the originals, they give us equally a view, not only of the persons and dresses of our ancestors, but also of their customs, manners, arts and employments, their arms, ships, houses, furniture, &c. and enable us to judge of their skill in drawing. The figures in those paintings are often stiff and formal; but the ornaments are in gemeral fine and delicate, and the colours clear and bright, particularly the gold and azure. In some of these illuminations the passions are strongly painted. After the introduction of printing, this elegant art of illuminating gradually declined, and at length was quite neglected. IMAGE, in optics, is the appearance of an object made either by reflection or refraction. In all plane mirrors, the image is of the same magnitude as the object, and it appears as far behind the mirror as the object is before it. In convex mirrors, the image appears less than the object; and farther distant from the centre of the convexity than from the point of reflection. By the following rule, the diameter of an image projected in the base of a convex mirror may be found. “As the distance of the object from the mirror is to the distance from the image to the glass, so is the diameter of the object to the diameter of the image.” IMAGINATION, a power or faculty of the mind, whereby it conceives and forms ideas of things communicated to it by the outward organs of sense. IMITATION, in literary matters, the act of doing, or striving to copy after,

or become like to another person or thing. IMITATIVE, in music, a term applicable to that music which is composed in imitation of the effects of some of the operations of nature, art, or human passion, as the rolling of thunder, swiftness of lightning, agitation of the sea, bellowing of the winds or waves, &c. Imitation is likewise a technical term, for a studied resemblance of melody between the several passages of the harmonical parts of a composition. IMMATERIAL, something devoid of matter, or that is pure spirit : thus, God, angels, and the human soul, are immaterial beings. IMMEMORIAL, in law, an epithet given to the time or duration of any thing whose beginning we know nothing of In a legal sense, a thing is said to be of time immemorial, or time out of mind, that was before the reign of King Edward 11. IMMENSITY, an unlimited extension, or which no finite and determined space, repeated ever so often, can equal. IVIMERSION, that act by which any thing is plunged into water, or other fluid. See Fluid. IMM Ension, in astronomy, is when a star or planet is so near the sun, with regard to our observations, that we cannot see it; being as it were enveloped and hidden in the rays of that luminary. It also denotes the beginning of an eclipse of the moon, or that moment when the moon begins to be darkened, and to enter into the shadow of the earth ; and the same term is also used with regard to an eclipse of the sun, when the disk of the moon begins to cover it. In this sense emersion stands opposed to immersion, and signifies the moment wherein the moon begins to come out of the shadow of the earth, or the sun begins to show the parts of his disk which were hid be. fore. Immersion is frequently applied to the satellites of Jupiter, and especially to the first satellite, the observation whereof is of so much use for discovering the longitude. The immersion of that satellite is the moment in which it appears to enter within the disk of Jupiter, and its emer. sion the moment when it appears to come out. The immersions are observed from the time of the conjunction of Jupiter with the sun, to the time of his opposition; and the emersions from the time of his opposition to his conjunction.

IMMUTABILITY, one of the divine attributes, founded on the absolute perfection of the Deity. ... The immutability of God is two-fold, physical and moral. The first consists in this, that the divine essence does not, nor possibly can, receive any alteration ; and the moral immutability is founded on the perfection of his nature, whereby he always wills the same things, or such as are best on the whole. IMPALED, in heraldry, when the coats of a man and his wife, who is not an heiress, are borne in the same escutcheon, they must be marshalled in pale; the husband's on the right side, and the wife’s on the left: and this the heralds call baron and feme, two coats impaled. If a man has had two wives, he may impale his coat in the middle between theirs; and if he has had more than two, they are to be marshalled on each side of his, in their proper order. IMPALPABLE, that whose parts are so extremely minute that they cannot be distinguished by the senses, particularly by that of feeling. IMPARLANCE, is a petition in court, for a day to consider or advise what answer the defendant shall make to the action of the plaintiff; being a continuance of the cause till another day, or a larger time given by the court, which is generally till the next term. IMPASSIBLE, that which is exempt from suffering, or cannot undergo pain or alteration. The stoics place the souls of their wise men in an impassible or imperturbable state. IMPATIENS, in botany, a genus of the Syngenesia Monogynia class and order. Natural order of Corydales. Gerania, Jussieu. Essential character; calyx twoleaved : corolla five-petalled, irregular, with a cowled nectary; capsule superior, five-valved. There are twelve species, of which I. balsamina, garden balsam, is an annual plant, about a foot and a half in height, dividing into many succulent branches ; leaves long and serrate; the flowers come out from the joints of the stem, upon slender peduncles, an inch in length, each sustaining a single flower. In its wild state it is two feet, or more, in height, round, hispid, juicy, with a white stem, and ascending branches. It is a native of the East Indies, China, CochinChina, and Japan ; the Japanese use the juice prepared with alum for dyeing their hails red. By culture this plant is very much enlarged, and becomes very branching. Mr. Millar tells us, he has seen the 3tem seven inches in circuit, and all the

plants large in proportion, branched from top to bottom, loaded with its party.coloured flowers, thus forming a most beat:tiful bush. The varieties which cultivation has produced in this elegant flower are numerous. I. nolitangere, common yellow balsam, is also an annual plant; during the day the leaves are expanded, but at night they hang pendent, contrary to what is observed in most plants, which, from a deficiency of moisture, or a too great perspiration from heat, commonly droop their leaves in the day-time. When the seeds are ripe, upon touching the capsule they are thrown out with considerable force : hence the Latin name “impatiens,” and “noli tangere.” The whole plant is considerably acrid, and no quadruped, except perhaps the goat, will eat it. IMPEACHMENT, is the accusation and prosecution of a person in parliament, for treason, or other crimes and misdemeanors. An impeachment, before the Lords, by the Commons of Great Biotain, is a presentment to the most high and supreme court of criminal jurisdiction, by the most solemn grand inquest of the whole kingdom. A commoner cannot be impeached before the lords for any capital offence, but only for high misdemeanors; but a peer may be impeached for any crime. The articles of impeachment are a kind of bills of indictment, found by the house of commons, and af. terwards tried by the lords, who are, in cases of misdemeanors, considered not only as their own peers, but as the peers of the whole nation. By stat. 12. and 13 Wm. c. 2. no pardon under the great seal shall be pleadable to an impeachment by the commons in parliament; but the king may pardon after conviction. IMPEAchMENT of waste, signifies a restraint from committing of waste upon lands and tenements; and therefore he that has a lease, without impeachment of waste, has by that a property or interest given him in the houses and trees, and may make waste in them without being impeached for it; that is, without being questioned, or demanded any recompense for the waste done. IMPEDIMENTS, in law, persons under impediments are those within age, under coverture, non compos mentis, in prison, or beyond seas; who, by saving in our laws, have time to claim and prosecute the right, after the impediments removed, in case of fines levied, &c. IMPENETRABILITY, in philosophy, that property of body whereby it cannot be pierced by another; thus, a body, which so fills a space as to exclude all others, is said to be impenetrable. Or, by impenetrability is meant, the faculty which a body has of excluding every other body from the place that it occupies, in such manner that two bodies placed in contact can never occupy less space than that which they filled when they were separate. The impenetrability of solid bodies does not require to be proved, it strikes us at first view ; but fluids, having their particles perfectly moveable in every direction, and yielding to the slighest pressure, their impenetrability does not manifest itself so perceptibly as that of solid bodies. Taking the air for an example: so long as this fluid is not enclosed in something, its extreme mobility causes it to admit a free passage to all bodies which are moved through it; but in this case it is properly displaced, and not penetrated; for, if the air be included within the sides of a vessel, and another body be then presented to take its place, without suffering it to escape, it will exercise its impenetrability in the same manner as solid bodies. It is easy to be convinced of this by the aid of a very simple experiment, which any one may make : it consists in plunging a vessel vertically, with the orifice downwards, in another vessel filled with water to a certain height: the surface of the water, corresponding with the orifice of the first vessel, is depressed as this vessel itself descends; and this depression may be rendered more sensible by means of a little plate, or slip of cork, placed so as to float upon the surface of the water; nevertheless, this water is not excluded by the air occupying the immersed vessel; it is always raised within it by a certain quantity, which augments as the vessel is immersed to a greater depth : but it is sufficiently evident that this ascension is occasioned by the circumstance that the air is a compressible fluid, and therefore its volume is contracted into a smaller space, by the effect of the com

ression excited upon it by the surrounding water on all parts, in virtue of its weight. We must here notice a difficulty which appears to result from this, that when we have mingled certain bodies, the volume of the mixture is less than the sum of the volumes taken separately. This happens, for example, when we mix equal parts of alcohol and water ; the same also obtains, when we mingle, by fusion, copper with zinc, in order to form the compound metal called brass : it is then observed, that the density of the

mixture is augmented by about its tenth art. This apparent penetration is ow. ing to the circumstance, that the molecu. lat of the two bodies, in consequence of their respective formation, generally approach one another more than in the two bodies taken separately; there hence results, in the figure of the pores, such a change as diminishes the space equal to the sum of these pores. On the contrary, in the alloy of silver with copper, a kind of rarefaction is produced, such that the volume of the mixture is larger than the sum of the volumes of the two bodies, previous to fusion. IMPERATIVE, one of the moods of a verb, used when we would command, entreat, or advise: thus, go, read, take pity, be advised, are imperatives in our lanuage. IMPERATORIA, in botany, a genus of the Pentandria Digynia class and order. Natural order of Umbellatae, or Umbelliferae. Essential character: fruit roundish, compressed, gibbose in the middle, surrounded by a margin; petals inflex, emarginate. There is but one species, viz. I. ostruthium, master-wort, the root of which is thick, running obliquely in the ground; it is fleshy, aromatic, and has a strong acrid taste, biting the tongue and mouth; the leaves arise immediately from the root, having foot-stalks seven inches long, divided into three very short ones at the top, each sustaining a trilobate leaf, indented on the border; the foot-stalks are deeply channeled, and when broken emit a rank odour; the flower stalks rise two feet high, dividing into two or three branches, each terminated by a pretty large umbel of white flowers, whose petals are split; these are succeeded by oval compressed seeds, resembling those of dill, but larger. Linnaeus observes, that the floral leaves are opposite, that there is a petiolary, membranaceous, ventricose, stipule, one within another: It is a native of many parts of the Alps, Austria, Syria, Tyrol, Silesia, and Dauphine. IMPERFECT, something that is defec. tive, or that wants some of the properties found in other beings of the same kind : thus mosses are called imperfect plants, because almost all the parts of fructification are wanting in them; and for the like reason is the appellation imperfect given to the fungi and submarine plants. IMPERFEct numbers, such whose aliquot É. taken together do either exceed, or all short of that whole number of which they are parts: they are either abundant

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