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Opodeldoc. Liniment prepared by dissolving soap, camphor and oil of rosemary in diluted alcohol; soap liniment.

Opopanax. Gum resin from Pastinaca opopanax, a plant much like the parsnip. It resembles asafetida, though less strong.

Oporto. Seaport of Portugal, second in size and commercial importance; on the River Douro, 3 m. from its mouth; besieged by the pretender Michael 1832-33. Pop., 1878, 105,838.

Opossums. American Marsupials of two genera. Chironectes, the water-opossum, living in n. Brazil, resembles the Otter. It has 6 young at a birth. Didelphys contains many species, ranging from the size of a mouse to that of a cat. The dentition is ICPM. They have an opposable great-toe on the hind foot; the tail is naked, long, and prehensile. D. virginiana of N. America, 2 ft. long, besides tail, has a well

Oppolzer, THEODORE VON, 1841-1886. Austrian author of a most complete work on Theoretical Astronomy 1870-80, and of many papers and memoirs on astronomical subjects. Opportunists. Practical politicians who aim only at the possible; opposed to theorists and doctrinaires.

Opposite. Method of leaf arrangement, where each node of the stem bears two leaves, which then diverge from each other, as in the Sunflowers.

Opposite Angles. On opposite sides of intersecting lines or planes; opposed to adjacent.

Ops. Wife of Saturn; Roman goddess of plenty and fertility; protectress of agriculture.

Opsiometer. See OPTOMETER.

Optatianus, PUBLILIUS, 4th cent. Latin poet.

Optical Bench. Apparatus for studying the phenomena of diffraction. It con

sists essentially of a graduated bar carrying three upright holders sliding along the bar. The first carries a laterally adjustable Ramsden's eyepiece, furnished with a set of cross-wires. The second and third uprights carry the various diffraction apparatus, as a narrow slit.

Optical Bench.

a fine vertical wire, a biprism to produce interference. By means of the biprism and slit wave-lengths may be measured with this apparatus.

Optical Center. Point of reference on the principal axis of a lens, so situated that any ray of light whose direction within the lens passes through it suffers no angular deviation. In a double convex or double concave lens it is within the lens. In a plano-convex or plano-concave lens it is the point where the principal axis intersects the curved surface. If the lens be

K

A B'

P

Opossum (Didelphys marsupialis).

developed pouch, in which the young, about a dozen, are placed, and attached to the long teats, after a period of gestation of less than a month. They suckle thus for two months. In some species the pouch is rudimentary, and the young cling to their mother's tail with their own. Most species of opossums are S. American and insectivorous; some also secure birds and eggs; a few are strictly frugivorous.

Opoterodonta. Sub-order of Ophidia, including insectfeeding snakes, having short or rudimentary tail and traces of hind limbs. The facial bones are immovable, and the mouth not distensible. The eyes are covered by scales and are rudimentary. These animals are small and live in the earth in sub-tropical regions, coming out like earth-worms when it rains. Typhlops is an example: only its upper jaw bears teeth. This and the Colubriform families, Tortricidae and Uropeltidæ, are sometimes grouped in one sub-order, Angiostomata.

Oppenheim. Town of Hesse-Darmstadt, on the Rhine. Here Conrad, son of Frederic II., was defeated 1247. Pop. ab. 3,500.

Oppenheim, HERMANN, b. 1858. German writer on nervous diseases.

Oppert, JULES, b. 1825. Prof. Coll. de France 1874; writer on Oriental antiquities.

Oppian, 2d cent. Greek poet, author of Halieutica, upon fishing, and possibly of Ixeutica, upon fowling, and Cynegetica, on hunting.

Oppian Law. In Rome, 213-193 B.C. It forbade women to possess more than one ounce of gold, to wear a dress of different colors, and to ride in or near the city in a carriage.

Oppius, GAIUS, 1st cent. B.C. Biographer of Cæsar and Scipio. Fragments survive.

O Optical Center.

a converging meniscus, the optical center is entirely without it on the convex side; if a diverging meniscus, the point is on the concave side. In general this point is determined by drawing two parallel radii, one to each curved surface, and joining the points where these lines cut the surfaces: the intersection of this last line with the principal axis is the optical center.

Optical Circle. Apparatus for verifying the laws of reflection and refraction. It consists of a vertical graduated circle at the center of which may be fixed a small mirror at right angles to the plane of the circle, and around the circumference of which move two tubes with their axes always directed toward the center of the circle. The mirror is movable; to the front of the circle may be attached a cylindrical vessel half filled with water or some other transparent liquid. If a beam of light be passed down one of the tubes it becomes incident on the mirror or the surface of the water and the other tube may be placed so that the ray after reflection or refraction, as the case may be, passes through it; then by reading the position of the tubes from the arc, the various laws may be studied.

Optical Density. Different transparent media are found to transmit radiant energy, e.g., light, with different velocities, depending upon the nature of the substance. Of two media that one is said to have the greater optical density in which the velocity of propagation is the less. Again, if a ray of light be incident upon the surface separating two media at any angle between zero and the critical angle, that medium has the greater optical density in which the ray makes the less angle with the normal at the point of incidence. Optical density and mass density often correspond, though there are several notable exceptions.

Optical Illusion. See MIRAGE, IRRADIATION, REFLECTION and REFRACTION.

Optical Lever. Apparatus employed by Laplace and Lavoisier to multiply the effect produced by the linear expansion of a rod. One end of the rod is fixed, while the other rests against the short end of a lever movable in a vertical plane

and to the long arm of which is attached a mirror or telescope directed to a vertical scale. A spot of light, if reflected from the mirror to a distant scale, will indicate by a considerable displacement any small elongation of the rod. Similarly, a considerable range of the scale will pass over the field of the telescope if the latter be used instead of the mirror.

Optic Angle. See OPTIC AXIS.

Optic Axis. The principal optic axis of the eye is a straight line through the optical center of the crystalline lens and the center of the pupil. The optic angle is that between the principal optic axes of the two eyes when directed to the same point. As the optic angle decreases as the distance of the object viewed increases, it forms an important element in judging distances. The visual angle between any two points is the angle formed by the two lines joining the points to the optical center of one eye. The visual angle is of prime importance in estimating size.

Optic Axis OF A CRYSTAL. See DOUBLE REFRACTION.

Optic Nerve. Second cranial nerve, whose special function is to convey the visual sensations from the eye to the brain. It extends from the region of visual perception in the occipital lobe of the cerebrum by way of the base of the brain to the orbit, and is distributed in the interior of the eye as the RETINA (q.v.).

Optics. Branch of physics which treats of the phenomena of light. It considers the theories of light; the laws of its propagation and distribution; and the methods of measuring its intensity and quantity.

Optic Vesicles. Buds from the fore brain, which are to be developed into the retinal portion of the eye in Vertebrate embryos.

Optimates. Aristocratic or senatorial party in ancient Rome, opposed to the plebs or populares.

Optimism. View that whatever exists is good and right, and in some inscrutable way leads to good; that this either is, or tends to become, the best of all possible worlds.

Options. On the stock exchange, privilege of either demanding or making delivery of a certain stock or commodity at a given price within a specified time; known also as Puts and Calls.

Optogram. Permanent image of an external object, fixed upon the retina of an eye. A retina is of a purplish-red color. This coloring matter, called by Kühne Visual Purple or Rhodopsin, is readily bleached by light; so that Kühne obtained optograms of external objects by exposing the eye of a recently killed rabbit to a source of light, such as an opening in a shutter; and then, after removing the exposed eye, hardening the retina and fixing the image with a solution of alum. On examining the surface, a clear white image of the opening was visible upon a beautiful rose-red ground.

Optometer, or OPSIOMETER. Instrument devised by Stampfer for defining the distance of distinct vision. The

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and then withdrawing the object till the two images were seen as one. Such is the case when the object is at a distance from the eye equal to that of distinct vision.

Opus Operatum. R. C. doctrine that the grace of the sacraments depends solely upon Divine institution, and not on the spiritual state of the recipient (opus operantis).

Opzoomer, CORNELIS WILLEM, b. 1821. Prof. Utrecht 1846; progressive and rationalist writer.

Oracle. The Greek world possessed a number of shrines where the gods were believed to answer the inquiries of men, through signs which the priests interpreted, or sometimes through a dream, as at Oropus. Dodona was the oldest in Greece: here brazen caldrons were suspended to oak trees, and these, when impelled by the breeze, struck together, making sounds which the priests explained. At Delphi, the most famous of all, sacred to Apollo. the Pythia or priestess sat upon a tripod over the mouth of a cleft in the rock, whence issued a gas which, it is said, caused her to fall into convulsions; her ravings were translated in the responses by the attendants. Certain oracles pretended to speak with the voices of the dead. At Præneste, near Rome, the goddess Fortune was consulted by means of throwing certain lots. In the early period of Greek history the Delphic and other oracles exerted great influence. They were generally couched in ambiguous language: those at Delphi, and generally those at Dodona. were given in hexameter verse. Sometimes the shrine is termed an oracle. See DELPHI, DODONA, FORTUNA, TROPHO

Berteling's Compound Optometer for Correcting Errors
of Refraction.

principles upon which it depends were deduced by experiments performed by Scheiner, which consisted in viewing a small object through two minute openings very near together

Orange (Citrus aurantium).

varieties. It is closely allied to the citron, lemon and lime. Oranges are evergreen, and bear fruit and flowers simultaneously. They have been extensively cultivated in Florida and Louisiana; in the former the trees were killed by the frost in 1895.

Orange. City of Essex co., N. J., 12 m. w. of New York; part of Newark till 1806. Pop., 1890, 18,844.

Orange. Former principality in s.e. France; claimed by the princes of Nassau from 1531; ceded to France 1713.

Orange. River of s. Africa. It rises in the mountains of Natal and the Transvaal, and flows generally w. to the Atlantic. Length ab. 1,150 m., drainage area 400,000 sq. m.

Orange III. See HELIANTHIN.

Orange, FORT. Erected 1623 by Dutch W. India Co. near site of Albany. N. Y.

Orange, PRINCE OF. See WILLIAM OF NASSAU and NASSAU. Orange Free State. Republic of S. Africa, lying between Cape Colony and the S. African republic. The surface is high (altitude 4,000 ft.) and is an undulating plain. It was founded 1836 by Boers from Cape Colony. They speak a corrupted Dutch dialect, and are nomadic and agricultural. Area 48,000 sq. m.; pop., 1890, 198,503, of whom 77,716 were white.

Orange Grass. Sarothra gentianoides. Herb of the St. John's Wort family, native of e. N. America; known also as Pine-weed.

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Orangemen. Association of Irish Protestants, first so called after 1688, as favoring William of Orange against the Stuarts. The first Orange Lodge was formed in n. Ireland 1795. In 1835 there were 1,500 lodges in Great Britain and Ireland, in 1861 150,000 members in Canada. Its great days are Nov. 5, date of William's arrival at Torbay, July 1 and 12, battles of Aughrim and the Boyne. Riots sometimes attend their celebrations, as in New York July 12, 1871. See RIBBONISM.

Orange Oil. Extracted from orange-peel and water by distillation. It is fragrant.

Orange-Root. Hydrastis canadensis. Herb of the Buttercup family, native of e. N. America; known also as Yellow Puccoon.

Orang-Utan (SIMIA SATYRUS). Tailless Ape of Borneo, standing 4 ft. high, having long arms, with a span of over 7 ft. The thumbs and great toes are relatively short. The face is

Orang-Utan.

naked, the hair reddish brown, not abundant on the body. Adult males have a long beard. They live in jungles and sleep in nests high up in trees. In shape their brain approaches nearest to man's of all Apes.

Oratorio. Species of combined literary and musical entertainment, named from the oratory of St. Philip Neri in Rome. Though evidently an offspring of the mysteries, moralities, and miracle plays, the oratorio is traced from the dramatic representations with which Neri varied his religious instructions. As an art-form it has a history contemporary with that of the opera: the first was produced in Rome by Emilio del Cavalieri 1600; it was called La Rappresentazione dell' Anima e del Corpo, and employed all the elements found in operatic representations. In time the employment of scenery and action fell into disuse, and the oratorio took on the narrative or epical character which now distinguishes it from the opera, but a tendency toward the drama is visible in the sacred operas encouraged by Rubinstein, which deal with subjects borrowed from sacred story, and illustrate incidents which are not presented to the eye, many being impossible of scenic realization, but put before the imagination by means of stage directions. The Passions, also called Oratorios, had an independent origin in Germany, Handel, having grown out of an ancient church service. whose Messiah is the most familiar and popular oratorio extant, developed the form to its perfection in Italy. The com

posers most intimately identified with the history of oratorio were Cavalieri, Carissimi, Allessandra Scarlatti, Caldara. Leo, Stradella, Sachini, Paisiello and Hasse in Italy, Schütz, Keiser, Mattheson, Bach, Graun, Haydn, Spohr, Mendelssohn, Rubinstein and Liszt in Germany, Handel, Bennett, Sullivan and MacKenzie in England.

Oratory. Place for prayer; small room used for devotion, whether in a dwelling, convent, or church.

Oratory, PRIESTS OF THE. Order following a rule and obeying superiors, but taking no vows and retaining their property; founded by St. Philip Neri 1561.

Orbegozo, LUIS JOSÉ, 1795-1847. Pres. of Peru 1833, and under the confederation with Bolivia till 1838; exiled 1839.

Orbigny, ALCIDE D', 1802-1857. French naturalist, who made an exploration of S. America 1826-33; prof. at the Museum of Natural History, Paris, from 1852. Paléontologie Francaise, 14 vols., 1850-54.-His brother, CHARLES, b. 1806, wrote on geology and paleontology, especially on the Ammonites. Orbilius, PUPILLUS, ab. 113-ab. 15 B.C. Grammarian at Rome from 63 B.C.; teacher of Horace.

Orbit. Path which a planet or comet describes about the If undisturbed, this would be an ellipse, hyperbola, or parabola.

sun.

Orbitelariæ. See SPIDERS.

Orcagna, ANDREA (DI CIONE), ab. 1316-1376. Florentine painter and sculptor. The fine tabernacle in Or San Michele at Florence is his work. In painting he follows the methods and spirit of Giotto. His authentic pictures are not numerous; the best known are the frescoes of the Strozzi Chapel in Santa Maria Novella, Florence. The frescoes in Pisa long attributed to him are no longer considered his.

Orchard Grass. Dactylis glomerata. Strong growing, early, and nutritious grass. It is more valuable as meadow than as pasture grass, and is very objectionable as a lawn grass, from its habit of growing in tufts.

Orchardson, WILLIAM QUILLER, D.C.L., b. 1835. Scottish genre painter, of first rank within the limits of his school; in London since 1863; R.A. 1877.

Orcagna.

Orchestra. Company of instrumental musicians eployed in theater, opera, or symphonic concerts, distinguished from bands. Most of the players use instruments of the viol family, of which four varieties are employed, viz., violins, violas, violoncellos, and double-basses. These are all used in numbers, and form a choir called the Strings. A second choir is composed of the wind instruments of wood. viz., flutes, oboes, clarionets, and bassoons, with their related forms, the piccolo flute, English horn, corno di bassetto, bass clarionet, and contra-bassoon, collectively called the Woodwinds; a third choir are the brasses, viz., cornets or trumpets, horns, trombones, and tubas, with their variations. Finally, there are the instruments of percussion, ordinarily limited to a pair of kettle drums. Practically the range of the orchestra is coextensive with that of the pianoforte. The wood-winds are generally represented in pairs, though the number of each is sometimes doubled for the purpose of maintaining a balance with the strings, which normally make up three-fourths of an orchestra.

Orchestration. Art of writing music for the various instruments of an orchestra. It is a work of detailed elaboration, which follows the conception of a composition and frequently its completion, at least in sketch form. Skill in the art is conditioned upon knowledge of the capacity of the various instruments composing an orchestra and their characteristic qualities of tone, singly and in combination. Text-books on it have been written by Berlioz, Gevaert, E. Prout, and F. Corder.

Orchidaceae. Natural family of flowering plants, of the class Angiosperma and sub-class Monocotyledons, comprising ab. 370 genera and 5,000 species, very widely distributed through the temperate and warmer regions of the earth; called the Orchid family.

Orchidaceous. Pertaining to or resembling orchids; especially their corollas.

Ord, EDWARD OTHO CRESAP, U.S.A., 1818-1883. Major-gen. U.S. Vols. 1861-66, holding commands in Miss. and Va.; Brig.gen. U.S.A. 1866; retired 1880.

Ord, GEORGE, 1781-1866. American naturalist, biographer of Alexander Wilson, parts of whose Ornithology he edited 1813-25.

Ordeal. Primitive form of trial by appeal to divine intervention; known among ancient nations; often resorted to in Europe through the Middle Ages. There were various forms: trial by battle, still surviving in the duel; by fire, or boiling water or oil, immunity being a proof of innocence; by cold water, innocence shown by the sinking of the accused; by bread, the guilty being supposed unable to swallow a piece over which certain adjurations had been said; by the bier, blood flowing from a murdered body when touched by the murderer; and others. The ordeal was sometimes used by church officers, but from the 6th century was disapproved by the popes. Trial by battle was not actually abolished in England till 1819.

Order. Group of animals or plants, composed of families having common characters; subdivision of a class. E.g., the class Reptilia includes the orders Snakes, Lizards, Turtles, and Crocodiles.

Order. In Classic Architecture, this denotes a column with its support and entablature. According to the form of these members, and especially of the capital, a building or a single range of columns is said to be of the Doric, Ionic or Corinthian, or, in Roman architecture, of the Tuscan or the Composite order.

Order. In Law, direction by a court to pay money, deliver property, or the like.

Order, IN MATHEMATICS. The basis of classification varies with the character of the subject matter. Series have orders dependent upon the number of constant elements forming the law of the series. Orders of loci depend upon the degree of the equation which gives the law of the locus. The order of contact between the curves refers to the number of successive derivation of their common ordinate, which are equal. The order of a determinant depends on the number of elements involved.

Ordericus, VITALIS, 1075-ab. 1143. Historian of Normandy, where he was a monk of St. Evroul, and of his native England. His book, pub. 1619, tr. 1853-56, is of value chiefly from 1066 on. Orderly. Soldier detailed to report to an officer to carry any military order or perform any personal service; also one designated to be responsible for the orderly character of quarters occupied by several.

Orderly Sergeant. First sergeant of a company, troop, or battery in the U. S. service.

Order of Battle. Tactical disposition of the different parts of an army preparatory to offering battle. The principal orders are the parallel, the oblique, the convex, and concave.

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Orders, GENERAL. Announce the time and place of issues and payments, hours for roll calls and duties, police regulations and prohibitions, returns to be made and their forms, laws and regulations for the army, promotions and appointments, eulogies or censures, the results of trial by general courts-martial in all cases of officers or of soldiers involving matters of general interest and importance, and, generally, whatever it may be important to publish to the whole command. Special orders are such as concern individuals or relate to matters that need not be made known to the whole command.

Orders, MILITARY. That of St. John of Jerusalem, known as Hospitalers, Knights of Rhodes and of Malta, was founded 1120 or earlier. The TEMPLARS (q.v.) were organized 1119-28, and destroyed 1308-15. See also TEUTONIC KNIGHTS.

Orders in Council. Instructions or regulations of Privy Council, either under authority of Parliament or by exercise of the royal prerogative.

Orders of Architecture. See ARCHITECTURE.
Orders of Goods. See GOODS.

Orders of the Ministry. In most Protestant bodies one, Presbyter; in the Anglican three, Deacon, Presbyter, and Bishop; in the R. C. these with four MINOR ORDERS (q.v.). Ordinance. In Architecture, the arrangement or composition of an order.

Ordinance. Local regulation by a municipality. Ordinance of 1787. Passed by Congress July 13, regarding the Northwest Territory.

Ordinary. In the Roman Empire, judicial officer of original jurisdiction, generally pres. of a province; in canon law, bishop of a diocese; in modern law, officer who has succeeded to the bishop's jurisdiction over probate and divorce causes. Ordinary Ray. See DOUBLE REFRACTION.

Ordinate. One of two lines determining position in Cartesian Coördinates. The ordinate of any point is its distance from the axis of abscissas, measured on or parallel to the axis of ordinates.

Ordination. Designation, usually by imposition of hands, to an ecclesiastical office, especially that of Presbyter; commonly regarded as availing for the whole life.

Ordnance. See CANNON, HOWITZER, and MORTAR. Ordnance and Ordnance Stores. Include cannon and artillery carriages and equipments, and all property supplied by the Ordnance Department.

Ordnance Department. Staff Corps of U.S. army under one chief (Brigadier-general), charged with procuring and distributing the necessary ordnance supplies for the Government, and care of arsenals and depots for their manufacture and safe keeping. The arsenals and depots are at Allegany, Pa.; Augusta, Ga.; Benicia, Cal.; Columbia, Tenn.; Fort Monroe, Va.; Philadelphia, Pa.; Indianapolis, Ind.; Augusta, Me.; Governor's Island, N.Y.; Rock Island, Ill.; San Antonio, Texas; Sandy Hook Proving Ground, N. J.; Springfield, Mass.: St. Louis Powder Depot, Mo.; U. S. Powder Depot at Dover, N. J., Watertown, Mass., and West Troy, N. Y. During the fiscal year ending June 30, 1893, the expenditures were $3,702,000.

Ordnance Survey. Government survey of Great Britain, first completed in 1755, under the direction of the Ordnance Department; since elaborated.

Ordovician. Cambro-Silurian or Lower Silurian rocks of earlier writers; broadly subdivided thus: (See COLUMN.)

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which agree in having great length and breadth compared with their thickness, are the most common modes of occurrence. though many modifications of these typical forms are recognized. Mass deposits, segregations, impregnations, bunches, pockets, nests, etc., are irregular in shape. No single theory of origin applies to all deposits, and no one classification has met with universal approval. The literature of ore-deposits is extensive. Among many writers on this branch of economic geology may be mentioned Burat, von Cotta, Gaetzschmann, Grimm, von Groddeck, Henwood, Kemp, Köhler, Phillips, Posepny, and Whitney. Valuable descriptions of individual deposits, and elaborate discussions of theories, are to be found in the reports of geological surveys, in scientific and technical periodicals, and in the transactions of societies.

Ore Dressing. Operations of breaking, crushing, washing, sizing, sorting, etc., employed in separating ore from worthless rock, or in bringing a portion of the ore to a state of greater richness.

Oregon. One of the western States, on the Pacific coast. Along the coast extends a low range of mountains or hills, which may be considered as an extension n. of the Coast Ranges of Cal. E. of this is the valley of the Willamette, which may be considered a continuation of that of Cal. This is succeeded e. by the Cascade Range, a broad volcanic plateau, above which rise volcanic peaks, and from which one descends to the great semi-arid plateau occupying the e. twothirds of the State. In the n.e. part of this area rise the Blue Mts., with heights of perhaps 9,000 ft. The s. part of this plateau forms part of the Great Basin; the n. and e. parts are drained to the Columbia and Snake rivers. Its industries consist in the main of agriculture, with salmon fisheries and lumbering. O. originally included all the territory n. of the

View in the Cascade Mountains, Oregon.

42d parallel between the Pacific and the Rocky Mts., and was claimed by the U. S. as part of the Louisiana purchase. Serious and prolonged complications over the territory arose with England, which laid claim to the territory by reason of alleged prior discovery and settlement. The difficulties were provisionally adjusted 1818 by a treaty of joint occupation, and 1846 by a treaty in which England recognized the 49th parallel of latitude as the n. boundary of the U. S. O. was organized as a territory 1848, and admitted as a State 1859. Railroads, in 1894, 1.481 m. 430.000 cases of salmon were shipped in 1890. Area 96,030 sq. m.; pop.. 1890, 313,767. Capital, Salem. Oregon River. See COLUMBIA. O'Reilly, JOHN BOYLE, 1844-1890.

Irish-American poet and journalist. A soldier and a Fenian, he was convicted of high treason 1866, and after a year's imprisonment was sent to western Australia, whence he escaped 1869. From 1874 he was owner and editor of the Boston Pilot.

Orel. City of Russia, on the Oka, 222 m. s. w. of Moscow; mainly burned 1848 and 1858. It has a large trade and some manufactures. Pop., 1890, 79,135.

Orélie Antoine (CHARLES DE TONNEINS), 1820-1878. French adventurer, King of Araucania (Patagonia) 1861; deposed by Chili and deported.

O'Rell, MAX. See BLOUET, PAUL.

Orenburg. Town of e. Russia, on the Ural; built 1743. It has considerable trade. Pop., 1891, 62,534. Oreodon. See OREODONTIDE.

Oreodontidæ. Family of Bunodont, even-toed Ungulates, represented by fossils from the Miocene and Pliocene formations of N. America. They combine characters of the Swine and Ruminants. Oreodon was of the size of a sheep, had fourtoed feet and complete dentition, which departs from the true Bunodont type in being like that of Selenodonts.

Orestes. Subject of several Greek tragedies: son of Agamemnon and Clytemnestra; saved from death by his sister Electra. He avenged his father's murder by slaying his mother and her paramour Ægisthus, was struck with madness and pursued by the Furies, but was acquitted by the Areopagus, and recovered his father's kingdom at Mycena.

Orfila, MATHIEU JOSEPH BONAVENTURE, 1787-1853. Minorcan physician and scientist, prof. Paris from 1819; writer on medicine and chemistry. Toxicologie, 1813. Orford. See WALPOLE.

Organ. See ORGANOGENY.

Organ. Most complete and capacious of instruments of music. Its fundamental principle is that exemplified in the ordinary toy whistle. It is therefore a wind instrument, its multitudinous voices being produced by the admission of air into the pipes from a magazine (wind-chest), into which it has been forced by bellows. The opening and closing of the pipes is accomplished by valves or slides, controlled by the fingers and feet of the player through the agency of keyboards, of which there are from two to five, one for the feet (pedals), the others for the hands (manuals). The pipes, which mount to thousands in the case of large instruments, are varied in size, to obtain degrees of pitch, and in material, shape, and device for the sake of variety in tone color. A distinction is made between flue pipes, in which the sound is produced by a current of air

impinging on the upper lip The New Organ in the Church of St. Lawof the pipe, as in the case of rence Jewry, Gresham St., London, Eng. the ordinary whistle, and setting the column of air in the tube to vibrating, and reed pipes, in which the sound is the result of the vibration of a tongue of metal, technically called a reed, inserted in the lower end of the pipe and agitated by the wind. The various systems of pipes are brought into service as required by means of mechanical devices, of which the commonest is the draw-knob. The organ in its simple form is an instrument of great antiquity. It seems to have been introduced in the Ch. ab. 650. See ORGAN PIPE.

Organic Chemistry. Branch dealing with the transformation and decomposition of the hydrocarbons and their derivatives. Till 1828 it was held that organic compounds were fundamentally different from the inorganic or mineral substances, in that they were only found in living things, plants, and animals, and were therefore necessarily elaborated under the influence of the life force or vital principle. It was further held that no organic compounds could exist without the intervention of this life force. In 1828 Wöhler succeeded in preparing urea artificially. In rapid succession a large number of the compounds occurring in plants and animals were made by synthetical operations in the laboratory. At present large factories are engaged in the production of coloring matters. flavoring extracts, perfumes, sweetening substances, etc.. formerly obtained from plants. There are now ab. 200 hydrocarbons known. Upon oxidation each yields an alcohol. These in turn yield an aldehyde, and then an acid. The alcohols also

Orelli, JOHANN KASPAR VON, 1787-1849. Prof. at Zurich from 1819: editor of Cicero, Horace, and Tacitus. Latin Inscriptions, 1828.

Orelli, KONRAD VON, Ph.D., b. 1845. Prof. Basel 1873. O.T. Prophecy, 1882, tr. 1885; commentaries on the Prophets, 1887-88.

replaced by the halogens or radicals. With every alcohol and most of the metals the acids yield derivatives. New substances and new classes of substances are being discovered daily; the field is constantly widening, and is engaging the attention of a large majority of chemists.

Organic Radicle. See RADICLES.