the other metal was IRIIDUM, which see. The osmium was obtained by heating the black powder with pure alkali in a silver crucible. The oxide of this metal combines with the alkali, may be expelled by an acid, and being very volatile, may be obtained by distillation. It does not redden vegetable blues, but stains the skin of a deep red or black. The oxide, in solution with water, has no colour; but by combining with alkali or lime, it becomes yellow. With an infusion of nut-galls, it gives a very vivid blue colour. It is precipitated by all the metals, excepting gold and platina. An amalgam may be formed with mercury, by agitating it with the aqueous solution of this oxide. When this amalgam is heated, the mercury is driven off, and the pure metal remains behind, in the state of black powder. This metal was called osmium, on account of the strong smell of the oxide.

OSMUNDA, in botany, a genus of the Cryptogamia Filices class and order. Natural order of Filices or Ferns. Generic

character: capsules distinct, disposed in a raceme, in such a manner as to look the same way, or else heaped on the back of the pinna or division of the frond, sessile, sub-globular, opening transversely, without any ring: seeds very many, extremely minute. There are twenty-seven spe

cies.

OSSIFICATION, the formation of bones, but more particularly the conversion of parts naturally soft to the hardness and consistence of bones. All concretions, which make their appearance in the solids of the animal body, may be comprehended under this title with propriety, because they have a close resemblance to, and are composed of, similar constituents with BONE, which see. In the pineal gland concretions have been found, which consist of phosphate of lime. The same is true of concretions found in the salivary glands, in the prostate, and the liver; and also in pulmonary concretions. The latter, however, are found to contain phosphate and carbonate of lime, and in some cases no phosphate, but

Carbonate of lime............ ..82
Animal matter and water.......18

100

OSTEOLOGY, that branch of anatomy which treats of the bones.

OSTEOSPERMUM, in botany, a genus of the Syngenesia Polygamia Necessaria class and order. Natural order of Com

positæ Discoideæ. Corymbiferæ Jussieu. Essential character: calyx simple, or in two rows, many-seeded, almost equal; seeds globular, coloured, bony; down none; receptacle naked. There are seventeen species.

OSTRACION, the trunk-fish, in natural history, a genus of fishes, of the order Cartilaginei. Generic character: teeth cylindric, pointing forwards and rather blunt; body mailed by a complete long covering. There are twelve species, We shall notice only the O. triqueter, or the triangular trunk-fish: it is about twelve inches long, and is completely, except to a very short distance from the tail, surrounded with a bony covering, divided into hexagonal spaces, and overspread with a diaphanous epidermis, resembling thus the armadillo among quadrupeds. It is a native of the American and Indian seas, is thought a high delicacy in India, and lives, it is supposed, on worms and shell-fish.

OSTREA, the oyster, in natural history, a genus of the Vermes Testacea class and order. Animal a tethys: shell bivalve, generally with unequal valves and slightly eared; hinge without teeth, but furnished with an ovate, hollow, and mostly lateral transverse grooves. About 150 species have been enumerated, and classed into sections and subsections. A. furnished with ears and radiate; scallop. B. rough and generally plated on the outside; oysters. C. hinge with a perpendicular grooved line. Most of this genus are furnished at the hinge internally with numeral parallel transverse grooves in each valve, and are immediately distinguished from the genus arca, in not having teeth alternately locked in each other. Scallops leap out of the water to the distance of half a yard, and, opening the shells, eject the water within them: after which they sink under the water, and suddenly close the shell with a loud snap. O. maxima; shell with about fourteen rounded and longitudinal striate rays; it is found in most European seas, in large beds, whence they are dredged up and pickled and barrelled for sale. This, we are told, is the shell which was formerly worn by pilgrims on the hat or coat, as a mark that they had crossed the sea, for the purpose of paying their devotions at the Holy Land; in commemoration of which it is still preserved in the arms of many families. O. eduli: shell nearly orbicular and rugged, with undulated imbricate scales; one valve flat and very entire. Of this species there are many va

rieties. They inhabit European and Indian seas, affixed to rocks, or in large beds; the fish is well known as a palata ble and nutritious food. The shell is of various sizes, forms and colours; within white, and often glossy like mother of pearl; the old shells have often an anomia fixed to them, and are frequently covered with serpulæ, lepades, sertularia, and other marine productions. The following accouut has been given by Dr. Sprat of the treatment of oysters, in Great Britain.

In the month of May the oysters cast their spawn, (which the dredgers call their spats); it is like to a drop of a candle, and about the bigness of a halfpenny. The spat cleaves to stones, old oystershells, pieces of wood, and such like things at the bottom of the sea, which they call cultch. It is probably conjectured that the spat in twenty-four hours begins to have a shell. In the month of May, the dredgers (by the law of the Admiralty Court) have liberty to catch all manner of oysters, of what size soever. When they have taken them, with a knife they gently raise the small brood from the cultch, and then they throw the cultch in again, to preserve the ground for the future, unless they be so newly spat that they cannot be safely severed from the cultch; in that case they are permitted to take the stone, or shell, &c. that the spat is upon, one shell having many times twenty spats. After the month of May, it is a felony to carry away the cultch, and punishable to take any other oysters, unless it be those of that size (that is to say), about the bigness of a half-crown piece, or when, the two shells being shut, a fair shilling will rattle between them. The places where the oysters are chiefly catched, are called the Pont Burnham, Malden, and Colne Waters; the latter taking its name from the river of Colne, which passeth by Colne Chester, gives the name to that town, and runs into a creek of the sea at a place called the Hythe, being the suburbs of the town. This brood and other oysters they carry to creeks of the sea, at Brickel Sea, Mersey, Langno, Fingrego, Wivenho, Tolesbury, and Saltcoase, and there throw them into the channel, which they call their beds or layers, where they grow and fatten, and in two or three years the smallest brood will be oysters of the size aforesaid.

Those oysters which they would have green, they put into pits about three feet deep, in the salt marshes, which are over

flowed only at spring tides, to which they have sluices, and let in the salt water until it is about a foot and a half deep. These pits, from some quality in the soil co-operating with the heat of the sun, will become green, and communicate their colour to the oysters that are put into them, in four or five days; though they commonly let them continue there six weeks or two months, in which time they will be of a dark green. To prove that the sun operates in the greening, Tolesbury pits will green only in summer; but that the earth hath the greater power, Brickel Sea pits green both winter and summer; and for a further proof, a pit within a foot of the greening pit will not green; and those that did green very well, will in time lose their quality.

The oysters, when the tide comes in, lie with their hollow shell downwards, and when it goes out they turn on the other side; they remove not from their place, unless in cold weather, to cover themselves in the ouse. The reason of the scarcity of oysters, and consequently of their dearness, is because they are of late years bought up by the Dutch.

There are great penalties, by the Admiralty Court, laid upon those that fish out of those grounds which the court appoints, or that destroy the cultch, or that take any oysters that are not of size, or that do not tread under their feet, or throw upon the shore, a fish which they call a five-finger, resembling a spur-rowel, because that fish gets into the oysters when they gape, and sucks them out. The reason why such a penalty is set upon any that shall destroy the cultch is, because they find that, if they be taken away, the ouse will increase, and the muscles and cockles will breed there, and destroy the oysters, they having not whereon to stick their spat. The oysters are sick after they have spat; but in June and July they begin to mend, and in August they are perfectly well; the male oyster is black-sick, having a black substance in the fin: the female white-sick (as they term it) having a milky substance in the fin. They are salt in the pits, salterin the layers, but salter at sea.

O. Virginica. Shell nearly equi-valve, thick, rough, and lamellous, one valve with a prominent beak, colour whitish or ochraceous, polished white within : length about 9 inches, breadth about 4 inches.

This is the shell emphatically called oyster" in the markets of the different towns of the United States. The animal is in high esteem as a delicious and nu

tritious food. Oysters are brought to the Philadelphia market principally from Egg-harbour and Delaware bay; the former are preferred for immediate use, having an agreeable sapid taste; the latter are generally dressed for the table; they have a thicker and rougher shell, and are fatter than those brought from Egg-harbour, or other parts of the coast, where the mixture of the fresh water is less abundant.

Those from the Delaware bay are known by the name of "fresh oysters," and the others by that of "salt oysters." They are merely varieties of the same species, notwithstanding their very different appearance and qualities.

OSTRICH. See STRUTHIO. OSYRIS, in botany, a genus of the Dioecia Triandria class and order. Natural order of Calcyflora. Eleagnæ, Jussieu. Essential character: calix trifid; corolla none: female, stigma roundish; drupe one-celled. There are two species, viz. O. alba, poet's casia, and O. japonica.

OTHERA, in botany, a genus of the Tetrandria Monogynia class and order. Natural order of Berberides, Jussieu. Essential character: calyx four-parted; petals four, ovate, flat; stigma sessile; capsule. There is but one species, viz. O. japonica, which has a shrubby stem, with round, striated, purple branches; leaves alternate, ovate, blunt, coriaceous, spreading, an inch and half in length: betioles semicylindric, smooth; flowers axillary, aggregate, peduncled; it is a native of Japan.

OTHONNA, in botany, African rag wort, a genus of the Syngenesia Polygamia Necessaria class and order. Natural order of Composite Discoidea. Corymbiferæ, Jussieu. Essential character; calyx one-leafed, multifid, subcylindrical; down almost none; receptacle naked. There are twenty-seven species, among which we shall notice the O. bulbosa, bulbous African rag-wort; this has a thick shrubby stalk, dividing into several branches, and rising five or six feet in height; the leaves come out in clusters from one point, spreading on every side; they are smooth, narrow at their base, enlarging gradually to their points; their edges are acutely indented like those of the holly; from the centre of their leaves arise the foot-stalks of the flowers, being five or six inches long, branching out into several smaller, each sustaining one yellow radiated flow er; these are succeeded by slender seeds crowned with down. Almost all the

Othonnas are natives of the Cape of Good Hope.

OTIS, the bustard, in natural history, a genus of birds of the order Gallina. Generic character; bill somewhat convex; nostrils oval and open; tongue bifid and pointed; legs long, and naked above the knee; only three toes. Gmelin mentions eleven species, and Latham nine. We shall notice only the following: 0. tarda, or the great bustard, is found in the plains of Europe, Asia, and Africa, but has never been observed in the New Continent. In England it is occasionally met with on Salisbury Plain, and in the wolds of Yorkshire, and formerly was not uncommonly seen in flocks of forty or fifty. It is the largest of British land birds, weighing often twenty-five or thirty pounds. It runs with great rapidity, so as to escape the pursuit of common dogs, but falls speedily a victim to the greyhound, which often overtakes it before it has power to commence its flight, the preparation for which, in this bird, is slow and laborious. The female lays her eggs on the bare ground, never more than two in number, in a hole scratched by her for the purpose; and if these are touched or soiled during her occasional absence, she immediately abandons them. The male is distinguished by a large pouch, beginning under the tongue, and reaching to the breast, capable of holding, according to Linnæus, seven quarts of water. This is sometimes useful to the female during incubation, and to the young before they quit their nest; and it has been observed to be eminently advantageous to the male bird himself, who, on being attacked by birds of prey, has often discomfited his enemies by the sudden and violent discharge of water upon them. These birds are solitary and shy, and feed principally upon grasses, worms, and grain. They were formerly much hunted with dogs, and considered as supplying no uninteresting diversion. They swallow stones, pieces of metal, and other hard substances. Buffon states that one was opened by the academicians of France, which contained in its stomach ninety doubloons, and various stones, all highly smoothed by the attrition of the stomach. See Aves, Plate XI. fig. 1.

O. tetrax, or the little bustard, is met with in many parts of Europe, particularly in France, where it is taken by nets. It is rarely seen in England; is shy and cunning; if molested will fly about two hundred paces, and then run so fast that a man cannot overtake it. Its flesh is like

that of the great bustard, rich and delicate, and it would appear worth while to attempt the domestication of both these birds.

OTTER. See LUTRA. OVAL, an oblong curvilinear figure, otherwise called ellipsis.

However, the proper oval or eggshape, differs considerably from that of the ellipsis, being an irregular figure, narrower at one end than at the other; whereas the ellipsis or mathematical oval, is equally broad at each end, though it must be owned these two are commonly confounded together, even geometricians calling the oval a false ellipsis.

The method of describing an oval chiefly used by artificers is by a string, the length of which is equal to the great. er diameter of the intended oval, and which is fastened by its extreme ends to two pins, placed in its longest diameter, then by holding it always stretched out with a pin or pencil carried round the inside, the oval is described, which will be longer or shorter, as the two fixed points are further apart.

OVIEDA, in botany, so named in honour of Gonsalvo Fernandez d'Oviedo, a genus of the Didynamia Angiospermia class and order. Natural order of Personatæ. Caprifolia, Jussieu. Essential character: calyx five-cleft; corolla tube subcylindric, superior, very long; berry globular, one-celled, quadripartile, fourseeded. There are two species, viz. O, spinosa, and O. mitis.

OVERSEERS of the poor. By 43 Elizabeth, c. 2. § 1 the churchwardens of every parish, or two substantial householders, to be nominated yearly in Easter week, or within one month after Easter, under the hand and seal of two justices of the peace of the county, shall be overseers of the same parish In general all persons are liable to serve, with some exceptions as to peers of the realm, clergymen, parliament men, attorneys, practis ing barristers, the president and mem. bers of the college of physicians, surgeons, and apothecaries free of the hall; dissenting ministers, prosecutors of felons having a Tyburn ticket, and soldiers actually serving in the militia. In extensive parishes a greater number of overseers are appointed under 13 and 14 Charles 2. c. 12. § 21; and by 17 Geo. II. c. 38, if an overseer dies, removes, or becomes insolvent, the justices may appoint another, and their appointment is subject to appeal to the sessions. By 43. Eliza. beth, c. 2. § 2. overseers shall, within fourteen days after the appointment of

new ones, deliver to them an account, to be allowed by two justices, and pay over balances due from them, which if not paid, may be levied by distress, and the party committed to prison by the justices until the balance is paid, and the account delivered in; and by 17 George II. c. 38. the account is to be verified by oath. If he removes, the overseer is to account in like manner. If he dies, his executors have forty days to account, and must pay the balance before any other debts.Their duty consists in raising the poor's rate, taking care of the poor, giving relief to casual poor, and removing persons who come to settle in a tenement under 10. a year, &c. without a certificate, They are also to bind out the children of poor persons, and in that case the infant parish apprentice and his master cannot vacate the indentures without the overseers. They also are to procure or ders of maintenance of bastards to be made, and bonds to be taken from the reputed father to indemnify the parish. It has been usual for overseers, in those cases, instead of taking a bond of indemnity, to accept of a sum of money, and discharge the father. But this has been lately held to be illegal, because it gives the overseers an interest to procure the death of the child. In cases of removal also, overseers should be careful not to execute the order in a harsh or improper manner, for if a person die in conse quence of a removal at a time of sickness, the overseer may be guilty of murder, and liable to an indictment. Overseers also should not improperly conspire to force persons who are with child of bastards to marry, and relieve the parish, for this is also indictable. By 17 George II. c. 38. if any person shall be aggrieved by any thing done or omitted by the churchwardens and overseers, or by any of his Majesty's justices of the peace, he may, giving reasonable notice to the churchwardens or overseers, appeal to the next general or quarter sessions, where the same shall be heard, or finally determined; but if reasonable notice be not given, then they shall adjourn the appeal to the next quarter sessions; and the court may award reasonable costs to either party, as they may do by 8 and 9 William, in case of appeals concerning settlements. See POOR. By 43 Elizabeth, c. 2. § 2. they forfeit 20s. on neglecting to meet in the vestry one Sunday in the month; and by 13 and 14 Charles II. c. 4. forfeit 51. for refusing relief to a person duly removed by warrant