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screw, o, (fig. 3.) cut upon it, to turn a wheel, p, by the teeth cut in its circumference; this wheel is in the same piece with a cylindric barrel, H H, shown separately (in fig. 4, Plate II.); it has a great number of short pins stuck in it, which as it revolves upon its pivots, catch the ends of a number of small levers called keys, r r r, and raise them; this depresses the other, t t t, ends, which are attached to the rods G, and consequently open the valves. There are as many of the levers, or keys, as there are pipes, each answering to a different note of the gamut; the pins in the barrel are so disposed, as to lift the keys in the same order and time as any piece of music for which the barrel has been previously made. The keys all turn upon one wire, as a centre, and to prevent their shifting sideways; and by that means missing the pins in the barrel intended for them, they move in small notches, cut by a saw in two pieces of brass plate, which are screwed to the edge of a piece of wood, K, and project below it; the wire which forms the centre for the keys is also fixed to the piece of wood, K, which is called the key-frame. A number of small pieces of mahogany are fixed to the keys att, and to these the rods, G, are jointed by a piece of leather glued to both : v v, are small screws going through the key-frame, and touching the piece of wood, t, their use is to adjust the levers, so that the ends, r r, shall form one straight line. The key-frame is not fastened down to the frame of the machine, but has a piece

of iron plate, w, fastened to each end, and .

turning upon screws fixed to the frame of the instrument, upon which the whole key-frame can be fitted as a centre; two screws through its ends, resting their points upon the frame, support it, and by screwing these out, the whole frame can be raised or lowered, to adjust the ends of the keys the proper distance from the centre of the barrel, H. By inspecting the plan and elevation, (fig. 1. and 3.) it will be seen, that the barrel is longer than the set of keys, by the distance of one of the keys from the other; the barrel can be moved along endways this quantity, and for this purpose it is mounted in a frame, (fig. 4.) which slides in a groove, shown in the section (fig. 2.); a small pin, P, (fig. 4.) is fastened to the frame, and comes through the case of the instrument; it has notches cut in it, which receive the sharp edge

of a bolt, L, (fig. o which holds the barrel in any place it is set. By moving the barrel endways a short distance, an entire new set of pins is presented to the keys, r r, which pins are disposed differently to the former ones, and consequently play a different tune; there are often five different sets, and as many notches, on the pin, P., (fig. 1.) Without some contrivance when the barrel is moved endways, its pins might catch some of the keys, and break or bend them: to avoid this, the bolt P, which confines the barrel, and prevents it being moved either way, is held down by another bolt, R, (fig. 7.) sliding across to the end of it; this bolt has a pin fastened to the backofit, which goes through the case of the instrument, (marked ar, fig. 2. and 3.) and when drawn back, presses down the end of a lever y, the other end of which lifts up the key-frame, and thus raises the keys up clear of the pins in the barrel, before it can be moved endways to play another tune. The regulator, D, is pressed down by two wire springs, which equalize the pressure upon the air contained in it, when, by #. bellows forcing in more air than the pipes require, and consequently, it accumulates in the regulator, it lifts up its lid, and the handle of a small valve, z, seen in the elevation, (fig. 1.) is pushed against a part of the frame; this opens the valves, and allows the air to escape, until the regulator sinks by the action of the two wire springs. From what we have said, a description of the operation of the instrument will be scarcely necessary. By turning the handle, the crank a, works the bellows, and supplies the air to the pipes; the endless screw turns the barrel, and its pins lift up the keys at the propertime, opens the valves, and admits the air into the pipes. When soft music is to be played, the stop, m, (fig. 2.) which has a handle coming through the case, is drawn out, and the other shoved in; this stops the passages to the wooden pipes, and opens the metal ones; for fuller music, the stop, m, is pushed in, and n drawn out; the wooden pipes are then used, and, for very grand and loud music, both sets are used, by drawing out both stops, and when both are in the soundcases, though the handle is still turned. For changing the tune, the bolt, R, is drawn back, this raises the key-frame :

fixed there, and the other bolt is then drawn back, and the pin, P, moved in or out to another notch ; the bolts are then to be returned. Several barrels are adapted to the same organ, to perform a great variety of tunes. ORGANICAL, in the ancient music, was that part performed by instruments. The organical comprehended three kinds of instruments, viz. the wind instruments, as trumpets, flutes, hautboys, &c.; stringed instruments, as lutes, lyres, violins, harpsicords, &c.; and pulsative instruments, or those played by beating with the hands or sticks, as drums, &c. ORGANICAL description of curves, is the description of them upon a plane by means of instruments, and commonly by a continued motion. The most simple construction of this kind is that of a circle, by means of a pair of compasses. The next is that of an ellipse, by means of a thread and two pins in the foci, or the ellipse and hyperbola, by means of the elliptical and hyperbolic compasses. ORGANZINE, in commerce, a description of silk usually imported from Italy into this country. It is of the utmost importance to the manufacturer, as none of the principle articles could be fabricated without it; and the Italians, aware of this, long kept the art of throwing it a most profound secret. It was introduced into this country by the enterprise and skill of Messrs. Thomas and John Lombe, the latter having, at the risk of his life, and with wonderful ingenuity, taken a plan of one of these complicated machines, in the King of Sardinia's dominions, from which, on his return, they established a similar set of mills in the town of Derby; and in consideration of the great hazard and expense attending the undertaking, a patent was granted to Sir Thomas Lombe, in 1718, for securing to him the exclusive privilege of working organzine for the term of 14 years; but the construction of buildings and engines, and the instruction of the workmen, took up so much time, that the 14 years were nearly expired before he could derive any advantage from it, in consequence of which he petitioned parliament, in 1731, to grant him a further term; but parliament considering it an object of national importance, granted him the sum of 14,000l. on condition that he should allow a perfect model of the machinery to be taken, and deposited in the tower of

London, for public inspection. Similar mills were, in consequence, set up in different parts of the country; but owing to the difficulties that were experienced in procuring raw silk of the proper size for organzine, the exportation of which from Italy was prohibited, and to the mills having subsequently found employment for other purposes, the quantities worked into organzine, for many years, bore scarcely any proportion to the imports from Italy; it has, however, been since revived and improved, in consequence of which it is now carried to a very considerable extent. The process which the silk undergoes to bring it into this state, consists of six different operations: 1. The silk is wound from the skein upon bobbins. , 2. It is then sorted. 3. It is spun, or twisted, on a mill in a single thread. 4. Two threads thus spun are doubled, or drawn together through the fingers of a woman, who at the same time cleans them, by taking out the slubs which may have been left in the silk by the negligence of the foreign reeler. 5. It is then thrown by a mill, that is, the two threads are twisted together, either slack or hard, as the manufacture may require; and it is wound at the same time in skeins upon a reel. 6. The skeins are sorted, according to their different degrees of fineness, and then the process is complete. Organzine was for many years made only from Italian silk, but when considerable improvements were made in the culture of silk in India, it suggested the possibility of throwing some of the finer silks of Bengal into organzine. The experiments of individuals were not very satisfactory, but in the beginning of 1794, the East India Company took up the subject, with the view of increasing the annual consumption of Bengal silk in this country; and having it in their power to select from their total import the silks most proper for this purpose, they have been enabled, at each subsequent sale, to put up from 80 to 100 bales of good Bengal organzine. It has been adopted successively in several branches of the manufacture ; and in the year 1808, when the prohibition of exportation from Italy produced a scarcity of the silks of that country, attempts were made to substitute Bengal organzine for all the purposes to which Italian organzine was applied; the result, however, appeared to be, that, for some particular articles, Italian organzine possesses pecu

liar properties, not to be found in any other kind of silk, ORGASM, a quick motion of the blood, whereby the muscles are made to move with great force. ORGUES, in the military art, are thick long pieces of wood pointed at one end, and shod with iron, clear one of another ; hanging each by a particular rope, or cord, over the gate-way of a strong place, perpendicularly, to be let fall in case of an enemy. Their disposition is such, that they stop the passage of the gate, and are preferable to herses or portcullises; because these may be either broke by a petard, or they may be stopped in their falling down; but a petard is useless against an orgue, for if it break one or two of the pieces, they immediately fall down again, and fill up the vacancy; or if they stop one or two of the pieces from falling, it is no hindrance to the rest. ORIGANUM, in botany, marjoram, a genus of the Didynamia Gymnospermia class and order. Natural order of Werticillatae. Labiatae, Jussieu. Essential character: strobile four-cornered, spiked, collecting the calyxes. There are twelve species, with several varietles. ORILLON, in fortification, is a small rounding of earth faced with a wall; raised on the shoulders of those bastions that have casements, to cover the cannon in the retired flank, and prevent their being dismounted by the enemy. ORIOLUS, the oriole, in natural history, a genus of birds of the order Pica. Generic character; bill conic, convex, very sharp and straight; mandibles, equally long; nostrils small, and lodged in the base of the bill, and partly covered; tongue divided and sharp-pointed. These birds are natives of America, are clamorous and voracious, appear in flocks, feed on fruits and grain, and frequently have pensile nests. Latham enumerates forty-five species; Gmelin fifty. We shall notice only those which follow : O. persicus, or the black and yellow oriole. A variety of this species, somewhat larger than a blackbird, and an inhabitant of South America, is the bird rendered remarkable for building nests in the form of an alembic, and nearly eighteen inches long, of dry grass, hog's bristles, and horse hair, or, what is called in that country, old man’s beard, a substance very like the hair of horses.

The bottom of this nest is hollow for the length of a foot, the remainder or upper part, for the space of six inches, is solid, and it is suspended at the extremity of a branch. It is particularly fond of, building on trees near houses, and several hundreds of these nests have occasionally been seen on a single tree.

O. icterus, or the Banana bird, is found in all the Caribbee islands, feeding on insects, and hopping like a magpie. These birds are domesticated in America, for the destruction of insects. In a state of nature, four or five will attack a large bird, and appear,after tearing it in pieces, to divide the spoil with great discrimination. They will occasionally attack men. Their nests are formed and susspended like those of the former species, to guard against snakes and other animals.

O. Baltimoreus, or the Baltimore bird, is called by the natives the fire-bird, and, when its feathers are most brilliant, naturally excites the idea or sensation of fire. These birds form pensile nests, secure from all depredation. They are about seven inches long, and inhabit North America. O. galbula, or the golden oriole, is as large as a blackbird, and of a fine golden yellow, with wings almost entirely black. It is common in several parts of Europe, particularly in France; but not seen so far north even as England. It is supposed to winter in Africa. Its nest is pensile, and the female is extremely attentive to her young, fearing no enemy in their defence, suffering herself to be taken in the nest with them,and continuing to sit over them in the cage till she dies. . It feeds on insects and fruits, and is considered as a delicacy for the table. For the red-rumped oriole, see Aves, Plate X. fig. 6. ORION, in astronomy, a constellation of the southern hemisphere, consisting of thirty-seven stars, according to Ptolemy; of sixty-two, according to Tycho; and of no less than eighty, in the Britannic catalogue. The lately improved telescopes have discovered several thousand stars in this constellation: of these, there are two of the first magnitude, four of the second, and several of the third and fourth. The stars of the first magnitude are Regel and Betelguese. Those of the second are, Bellatrix, on the left shoulder, and three in the belt, lying nearly in a right line, and at equal distances from each other.

ORNITHOGALUM, in botany, Star of Bethlehem, a genus of the Hexandria Monogynia class and order. Natural order of Coronariae. Asphodeli, Jussieu. Essential character: corolla six-petalled, upright, permanent, spreading above the middle ; filaments alternate, widening at the base. There are thirty-five species. ORNITHOLOGY, that branch of natural history,which considers and describes birds, their natures and kinds, their form, external and internal, and teaches their economy and uses; see Aves: also the several orders and genera, in the alphabetical order. Birds are divided, according to the form of their bills, into six orders, viz. Accipitres, as eagles, vultures, and hawks: Picae, as crows, jackdaws, humming-birds, and parrots: Anseres, as ducks, geese, swans, gulls; Grallae, as herons, woodcocks and ostriches: Gallinae, as peacocks, pheasants, turkies, and common fowls: and Passeres, comprehending sparrows, larks, swallows, &c. Birds are distinguished from quadrupeds by their laying eggs: they are generally feathered; some few are hairy, and instead of hands or fore-legs, they have wings. Their eggs are covered by a calcareous shell, and they consist of a white, or albumen, which nourishes the chick during incubation; and a yolk, which is so suspended within it as to preserve the side on which the little rudiment of the chicken is situated continually uppermost, and next to the mother that is sitting upon it. The yolk is in great measure received into the abdomen of the chicken, a little before the time of its being hatched, and serves for its support, like the milk of a quadruped, and like the cotyledons of young plants, until the system is become sufficiently strong for extracting its own food out of the ordinary nutriment of the species. ORNITHOPUS, in botany, bird’s foot, a genus of the Diadelphia Decandria class and order. Natural order of Papilionaceae, or Leguminosae. Essential character: legume jointed, round, bowed. There are five species. ORNITHORHYNCHUS paradorus, in natural history, a singular quadruped, remarkable for its structure. The head is similar to that of a duck, which would lead to the supposition that it belonged to an aquatic bird. Both jaws are as broad and low as those in a duck, and the calvaria has no traces of a suture, as is generally the case in full-grown birds. In the cavity of the skull there is a consi

derable bony falx, which is situated along the middle of the os frontis, and the ossa bregmatis. The mandible of this animal consists of a beak, the under part of which has its margin indented as in ducks, and of the proper instrument for chewing that is situated behind, within the cheeks. Dr. Shaw says it has no teeth, though Mr. Home found, in a specimen examined by him, two small and flat molar teeth on each side of the jaws. The fore part of this mandible or beak, is covered and bordered with a coriaceous skin, in which three parts are to be distinguished, viz. the proper integument, or the beak; the labiated margins of it; and a curious edge of the skin of the beak. Into these three parts of that membrane numerous nerves are distributed, intended, probably as the organs offeeling,a sense which, besides men, few mammalia enjoy: that is, few animals possess the faculty of distinguishing the form of external objects, ..o. qualities, by organs destined for that purpose, a property very different from the common feeling, by which every animal is able to perceive the temperature and presence of sensible ob. jects, but without being informed, by the touch of them, of their peculiar qualities. Thus the skin in the wings of the bat, and its ear, are supposed the organs of common feeling, by means of which they are enabled to flutter, after being blinded, without flying againstanything. The whiskers of many animals appear likewise to serve the same purpose of informing them of the presence of sensible bodies, and hence they have been compared to the antennae of insects. But to return to the ornithorhynchus: it is an animal which, from the similarity of its abode, and the manner of searching for food, agrees much with the duck, on which account it has been provided with an organ for touching, viz, with the integument of the beak richly endowed with nerves. This instance of analogy in the structure of a singular organ of sense in two species of animals, from classes quite different, is a most curious circumstance in comparative physiology, and hence the ornithorhynchus is looked upon as one of the most remarkable phenomena of zoology. There are two species, both inhabitants of New-Holland. OROBANCHE, in botany, broom-rape, a genus of the Didynamia Angiospermia class and order. Natural order of Personatae. Pediculares, Jussieu. Essential character; calyx bifid; corolla ringent; capsule one-celled, two-valved, many

to seeded; gland under the base of the germ. There are fourteen species. OROBUS, in botany, bitter vetch, a genus of the Diadelphia Decandria class and order. Natural order of Papilionacez, or Leguminosae. Essential character: calyx blunt at the base; the upper teeth deeper and shorter; style linear. There are sixteen species. ORONTIUM, in botany, a genus of the Hexandria Monogynia class and order. Natural order of Piperitae. Aroideae, Jussieu, Essential character: spadix cylindrical, covered with florets; corolla sixpetalled, naked; style none; follicles oneseeded. There are two species, viz. O. aquaticum, and O. japonicum. ORPHAN. In the city of London there is a court of record established for the care and government of orphans. ORPIMENT is a fine yellow powder, formed from a solution of the white oxide of arsenic in muriatic acid, to which is added a solution of sulphuretted hydrogen in water. It may also be obtained by subliming arsenic and sulphur by a heat not .#. to melt them. It is likewise found native in many parts of Germany and Italy, composed of plates that have a considerable degree of flexibility. Its specific gravity is 5.3. It is used as a pigment. The Chinese fashion vessels of different shapes, and their pagodas, of the mineral. 0RRERY, a curious machine for representing the motions and appearances of the heavenly bodies. See PLANETARIUM. ORTEGIA, in botany, so named in hohour of Joseph Ortega; a genus of the Triandria Monogynia class and order. Natural order of Caryophylleae. Essential character: calyx five-leaved: corolla none; capsule one-celled; seeds very many. There are two species, viz. O. Hispanica, Spanish ortegia, and O. dichotoma, forked ortegia, natives of Spain and Italy. ORTHOGRAPHIC projection of the ‘phere, that wherein the eye is supposed *taninfinite distance; so called, because the perpendiculars from any point of the sphere will all fall in the common intersection of the sphere with the plane of the projection. ORTHOGRAPHY, that part of grammar which teaches the nature and affections of letters, and the just method of spelling or writing words with all the is proper and necessary letters, making o, one of the four greatest divisions or branches of grammar,

Oathography, in geometry, the art of drawing or delineating the fore-right plan of any object, and of expressing the heights or elevations of each part. it is called orthography, from its determining things by perpendicular lines falling on the geometrical plane. ORthography, in architecture, the elevation of a building. This orthography is either external or internal. The external orthography is taken for the delineation of an external face or front of a building; or, as it is by others defined, the model, platform, and delineation of the front of a house, that is contrived, and to be built, by the rules of geometry, according to which pattern the whole fabricis erected and finished. This delineation or platform exhibits the principal wall, with its apertures, roof, ornaments, and every thing visible to an eye placed before the building. Internal orthography, which is also called a section, is a delineation or draught of a building, such as it would appear were the external wall removed. ORTHognaphy, in perspective, is the fore-right side of any plane, i. e. the side or plane that lies parallel to a straight line, that may be imagined to pass through the outward convex points of the eyes, continued to a convenient length. ORthogFAPHY, in fortification, is the profile or representation of a work; or a draught so conducted, as that the length, breadth, height, and thickness, of the several parts are expressed such as they would appear if perpendicularly cut from top to bottom. ORYCTOLOGY is the science which teaches the natural history of those animal and vegetable substances which are dug out of the earth, in a mineralized state. In the following slight sketch of the history of these substances it will be seen, that the remarkable situations in which they have been found, and the extraordinary changes which they have undergone, have led to the adoption of various contradictory and absurd notions respecting their nature and origin; which have been corrected, as just ideas have been obtained respecting the formation of the earth itself. Xenophanes, more than 400 years before Christ, was led to the belief of the eternity of the universe, by discovering the remains of different marine animals imbedded in rocks, and under the surface of the earth. Herodotus ascertained the existence of fossil shells in the mountains of Egypt, and was thereby induced to conclude, that the sea must have once covered those

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