Natural Phenomena. The most interesting of these is the rainbow, which consists of two bows, or arches, extended across the part of the sky, which is opposite to the sun. The innermost of the bows, and which is most commonly seen by itself, it being the principal rainbow, is part of a circle whose diameter is 82°, and is nothing more than an infinite number of prismatic spectra of the sun arranged in the circumference of a circle, the colors being the very same, and occupying the same space as in the spectrum produced from the sun's light. The red rays form the outermost portion, and the violet rays the innermost portion of the bow. The external or secondary bow is much fainter than the other, and has the violet outermost and the red innermost. It is part of a circle 104° in diameter. As the rainbow is never seen unless when the sun is shining, and when rain is falling between the spectator and the part of the horizon where the bow is seen, it is obvious that it depends upon the decomposition of the white light of the sun, by the refraction of the drops of rain and their subsequent reflection within the drops-an explanation sufficiently adequate, from the fact that rainbows are produced by the spray of waterfalls, and may be made artificially by scattering water with a brush or syringe when the sun is shining. The primary bow is the effect of one reflection and two refractions of the sun's rays by the drops of rain: the secondary one is formed by two reflections and two refractions. With in the primary rainbow, and immediately in contact with it, there have been seen what are called supernumerary rainbows, each of which consists of red and green. Their origin has not been explained. Lunar rainbows have been seen; but they differ in no respect from those formed by the solar rays, excepting in the faintness of their light. A halo is a circle, either composed of white light, or consisting of the prismatic colors, which is occasionally seen round the sun or moon. Parhelia are mock suns, which appear at places where two haloes or arches of luminous circles about the sun intersect each other. The prismatic haloes which are sometimes visible about the sun and moon, in fine weather, when white, thin, fleecy clouds are floating in the atmosphere, are called corona. Owing to the dazzling effect of the sun's rays, the haloes which surround his disk may be seen to most advantage by reflection in a pool of water. These phenomena are attributed to the crystals of ice and snow floating in the

atmosphere, and, in some cases, to the action of drops of rain of different sizes. The elevation of coasts, ships and mountains above their usual level, when seen in the distant horizon, has been long known and described under the name of looming. The name of mirage has been applied by the French to the same class of phenomena; and the appellation of fata morgana has been bestowed by the Italians to the singular appearances of the same kind, which have repeatedly been seen in the straits of Messina. When the rising sun throws his rays at an angle of 45° on the sea of Reggio, and neither wind nor rain ruffle the smooth surface of the water in the bay, the spectator, on an eminence in the city, who places his back to the sun and his face to the sea, observes, as it were upon its surface, numberless series of pilasters, arches and castles distinctly delineated; regular columns, lofty towers, superb palaces, with balconies and windows; extended valleys of trees, delightful plains, with herds and flocks; armies of men on foot and horseback, and many other strange figures, in their natural colors and proper actions, passing one another in rapid succession. When vapors and dense exhalations, rising to the height of about twenty feet, appear, then the same objects are seen depicted, as it were in the vapor, and suspended in the air, though with less distinctness than before. Captain Scoresby, when navigating the Northern seas, was able to recognise his father's ship when below the horizon, from the inverted image of it which appeared in the air. "It was," says he, "so well defined, that I could distinguish, by a telescope, every sail, the general rig of the ship, and its particular character, insomuch that I confidently pronounced it to be my father's ship, the Fame, which it afterwards proved to be; though, in comparing notes with, my father, I found that our relative position at the time gave our distance from one another very nearly 30 miles, being about 17 miles beyond the horizon, and some leagues beyond the limit of direct vision." In the sandy plains of Egypt the mirage is seen to great advantage. These plains are often interrupted by small eminences, upon which the inhabitants have built their villages, in order to escape the inundations of the Nile. In the morning and evening, objects are seen in their natural form and position; but where the surface of the sandy ground is heated by the sun, the land seems terminated, at a particular distance, by a general inundation, the vil

lages beyond it appearing like so many islands in a great lake, and between each village an inverted image of it is seen. This optical deception has been noticed from the remotest times. The prophet Isaiah alludes to it, when he says, "and the parched ground shall become a pool." The cause of these phenomena consists in variations in the refractive power of the atmosphere, which may be proved by actual experiment. This has been done in a variety of ways; but we shall only mention the method adopted by doctor Brewster. He held a heated iron above a mass of water bounded by parallel plates of glass as the heat descended slowly through the fluid, a regular variation of density, diminishing from the bottom to the surface, took place. On withdrawing the heated iron, and putting a cold body in its place, or even on allowing the air to act alone, the superficial stratum of water gave out its heat so as to produce a decrease of density from the surface to a certain depth below it. Through the medium thus constituted, the phenomenon of the mirage was observable in the finest manner. Colors of the Atmosphere. As the earth is surrounded with an atmosphere, varying in density from the surface of the globe, where it is the densest, to the height of about 45 miles, where it is extremely rare, and just able to reflect the rays of the setting sun, the rays of the sun, moon and stars are refracted into curve lines, unless when they are incident upon it perpendicularly. Hence the apparent altitude of the celestial bodies is always greater than their real altitude, and they appear above the horizon when they are actually below it. But while the solar rays traverse the earth's atmosphere, they suffer another change from the resisting medium which they encounter. When the sun, or any of the heavenly bodies, is considerably el evated above the horizon, its light is transmitted to the earth without any perceptible change; but when these bodies are near the horizon, their light must pass through a long tract of air, and, is considerably modified before it reaches the eye of the observer. The momentum of the red, or greatest refrangible rays, being greater than the momentum of the violet, or least refrangible rays, the former will force their way through the resisting medium, while the latter will be either reflected or absorbed. A white beam of light will therefore be deprived of a portion of its blue rays by its horizontal passage through the atmosphere, and the resulting color will be either orange or

red, according to the quantity of the least refrangible rays that have been stopt in their course; hence the rich and brilliant hue with which nature is gilded by the setting sun, and hence the glowing red which tinges the morning and evening cloud. We have already seen that the red rays penetrate through the atmosphere, while the blue rays, less able to surmount the resistance which they meet, are reflected or absorbed in their passage. It is to this cause that we must ascribe the blue color of the sky, and the bright azure which tinges the mountains of the distant landscape. As we ascend in the atmosphere, the deepness of the blue tinge dies away; and to the aeronaut who has soared above the denser strata, or to the traveller who has ascended the Alps or the Andes, the sky appears of a deep black, while the blue rays find a ready passage through the attenuated strata of the atmosphere. It is owing to the same cause, that the diver at the bottom of the sea is surrounded with the red light which has pierced through the superincumbent fluid, and that the blue rays are reflected from the surface of the ocean. Were it not for the reflecting power of the air, and of the clouds which float in the lower regions of the atmosphere, we should be involved in total darkness by the setting of the sun, and all the objects around us would suffer a total eclipse by every cloud that passed over his disk. It is to the multiplied reflections which the light of the sun suffers in the atmosphere that we are indebted for the light of day, when the earth is enveloped with impenetrable clouds. From the same cause arises the sober hue of the morning and evening twilight, which increases as we recede from the equator, till it blesses with perpetual day the inhabitants of the polar regions.-Colored Shadows. The shadows of bodies placed only in one light, and at a distance from all other bodies capable of reflecting light, must necessarily be black. In a summer morning, or evening, however, the shadows of bodies formed either by the light of the sun, or by that of a candle, have been observed to be blue: this obviously arises from the shadows being illuminated with the light of the blue sky. The colors thus produced vary in different countries, and at different seasons of the year, from a pale blue to a violet black; and when there are yellow vapors in the horizon, or yellow light reflected from the lower part of the sky, either at sunrise or at sunset, the shadows have a tinge of green, arising from the

union of these accidental rays with the blue tint of the shadow. If the light of the sun or of the candle be faint, then the shadow of the body, formed by the light of the sky, will be visible also, and the two shades will be the one blue and the other a pale yellow. This fact has been ascribed to the circumstance of the light of the candle and that of the rising and setting sun being of a yellowish tinge; but though this will increase the effect, it is not the main cause of it, as one of the shadows would be yellow, even if the light of the sun and the candle had been perfectly white. The phenomena of colored shadows are sometimes finely seen in the interior of a room, the source of one of the colors being sometimes the blue sky, and the other the green window blinds, the painted walls, or the colored furniture. Converging and diverging Beams. When the sun is descending in the west, through masses of open clouds, the diverging of his beams, rendered visible by their passage through numerous openings, forins frequently a very beautiful phenomenon. It is sometimes accompanied with one of an opposite kind, viz. the convergency of beams to a point in the eastern horizon opposite to the sun, and as far beneath the horizon as the sun is above it, as if another sun, throwing out divergent beams, were about to rise in the east. This phenomenon is rarely seen in perfection, and has never been observed until within a few years. In order to explain it, let us suppose a line to join the eye of the observer and the sun. Let beams issue from the sun in all possible directions, and let us suppose that planes pass through these beams, and through the line joining the eye of the observer and the sun, which will be their common intersection, like the axis of an orange, or the axis of the earth, through which there pass all the septa of the former, and all the planes passing through the meridians of the latter. An eye, therefore, situated in this line, or common intersection of all the planes, will, when looking at a concave sky, apparently spherical, see them diverging from the sun on one side, and converging towards the opposite point, just as an eye in the axis of a large globe would perceive all the planes passing through the meridians diverging on one side and converging on another.

OPTIMATES, with the Romans; the party of the nobility (tories), in contradistinction to the populares (men of the people-liberals).

OPTIMISM; that philosophical and re

ligious opinion which maintains that this world, in spite of its apparent imperfections, is the best, and could not be otherwise than it is. Even the Stoics and Plotinus were of this opinion. This name, however, is chiefly given to the doctrine of Leibnitz-that God has, among the possible worlds which presented themselves to his understanding, chosen and created the best. Leibnitz developed this doctrine in his Theodicea, particularly with reference to the doubts and objections of Bayle, on account of the evil in the world, and showed that what appears imperfect considered by itself, is by no means imperfect considered with regard to the whole, and that the single parts are the best when considered in their connexion with the whole. This philosophical doctrine was generally reduced to the dilemma-If this world were not the best, God either did not know a better one, or was unable or unwilling to create itsuppositions which impugn his omniscience, omnipotence or perfect benevolence. Hence the inference was, that this world must be considered the best. (See Leonh. Creuzer, Leibnitii Doctrina de Mundo optimo; see, also, the article Candide.)

ORACLES; responses given by persons who pretended to divine inspiration; also the places where the responses were uttered with certain prescribed ceremonies. There is not a sufficient stock of trustworthy information from antiquity to determine their origin or nature. The origin of the Egyptian oracles is dated at a period to which not even traditions, and much less historical monuments, extend. The oldest was that at Meroë; next, those at Thebes and Ammonium. In each of these places, Jupiter Ammon was the presiding deity. The oracle at Dodona (q. v. the oldest in Greece, was formed on the model of the last mentioned, but united the Egyptian and Pelasgian character. The account given by Herodotus of the origin of the Pelasgian oracle, shows that a colony from Africa attempted, by such an institution, to establish themselves in Greece. But a sacred tree in this place was, at an earlier period, oracular, and the rustling of its branches had been received as responses: consecrated women from Africa (prophetesses, the black doves of Herodotus) only dedicated this Pelasgian oracle to Jupiter Ammon. According to Ritter, the oracle of Dodona (formerly Bodona) points to the service of Buddha Of equal antiquity, perhaps, was the oracle in Boeotia, which first belonged to the

Earth, then to Themis, and afterwards was transferred to Apollo. Still later was instituted the oracle at Delphi (q. v.), which became the most important of all, partly from its favorable situation, and partly from its connexion with the council of the Amphictyons, at Pylæ. Besides, Jupiter had an oracle at Elis, at Pisa, and in a subterranean cave in Crete; and Apollo at Delos, where the whispering of the trees gave responses, at Miletus, where a sacred fountain, at Claros, not far from Colophon, where a consecrated river, inspired the priests, and many others. In addition to these, the oracle of Trophonius, at Lebadia, in Boeotia, and that of Amphiaraus, at Oropus, on the borders of Attica and Boeotia, were in high reputation in Greece. Juno had an oracle in the Corinthian territory; Hercules, at Bura, in Achaia, where answers were given by throwing dice; Bacchus, at Amphiclea, in Phocis, which returned answers in dreams, &c. Tzetzes mentions an oracle of Ulysses; and other heroes and prophets had theirs. The Romans had no domestic oracles, if we except the Albunea, the Cumman Sibyl, the Sibylline books, the oracle of Faunus and of Fortuna at Præneste (which belong to the earliest times, and afterwards lost their reputation), but had recourse to those of Greece and Egypt. In the founding of cities and colonies, the introduction of new governments, the undertaking of important enterprises, both in war and peace, and particularly in all cases of great necessity, the oracles were consulted, and rich gifts presented to them; their priests needed great watchfulness and prudence not to expose themselves. Darkness and ambiguity in the responses was the common resource. Sometimes, however, there were obvious failures. But, notwithstanding these, and notwithstanding well-known instances of corruption, they long maintained their standing, and sunk only with the freedom and independence of Greece. Under the reign of Theodosius, the temples of the prophetic deities were shut up or demolished. Van Dale and Fontenelle thought to explain the whole system of oracular responses by priestly management, founded on the popular delusion. Others have thought this insufficient to account for the fact that the wisest men in a refined nation received them as sacred for centuries, as in Greece. -See Clavier's Mémoire sur les Oracles des Anciens (1819).

ORAMA, DIORAMA. (See Panorama.) ORANGE (citrus aurantium); a low, evergreen, branching tree, bearing oblong,

oval, acute, smooth and shining leaves, inserted on winged leaf-stalks, by which character it is easily distinguished from the lemon. The flowers are white, containing about twenty stamens, and are disposed in clusters of from two to six upon a common peduncle. The fruit is globose, bright yellow, and contains a pulp, which consists of a collection of oblong vesicles filled with a sugary and refreshing juice: it is, besides, divided into eight or ten compartments, each containing several seeds. The principal varieties are the sweet or China, and the bitter or Seville orange; the Maltese orange is also deserving of notice, from its red pulp. Though now extensively cultivated in the south of Europe, the introduction of the orange is of modern date, and it was unknown in that continent till about the beginning of the fifteenth century. At the present time, it forms an extensive branch of commerce between the Mediterranean and the more northern countries. It is exceedingly long-lived, and is still esteemed young at the age of a century. An essential oil is obtained from the flowers, which is hardly less esteemed than the celebrated ottar of roses. Bergamot is a well-known perfume, obtained from the rind of a variety of the orange, and has received the name from the town of Bergamo, in Italy, where this variety is much cultivated. The wood of this tree is fine-grained, compact, susceptible of a fine polish, and is employed in the arts. The orange, together with the lemon, citron, lime, shaddock, and indeed almost the entire family aurantiacea, is a native of tropical Asia and the East Indies. A singular exception is found in our own country: a species of orange, bearing fruit of a very agreeable flavor, is extremely abundant in East Florida, and, according to the testimony of scientific travellers, is undoubtedly native: it has not, however, been accurately compared with other species, and, what is more remarkable, although mentioned by early travellers, has not hitherto found its way into systematic works on our botany.

ORANGE; an ancient principality in France, which, from the eleventh to the sixteenth century, had its own princes. Philibert of Châlons, the last prince, having died, without issue, in 1531, the principality passed, through his sister (who was married to the count of Nassau), to the house of Nassau. It continued in this family till the death (1702) of William Henry of Nassau-Orange (William III of England), when the succession became

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the subject of a long contest. The principal claimants were Frederic William I, king of Prussia (who claimed through his mother), and the prince of Nassau-Dietz, stadtholder of Friesland (who claimed by the will of William III). The king of Prussia, notwithstanding the protest of the other claimants, ceded the principality, by the peace of Utrecht (1713), to France. The reigning dynasty of the Netherlands is of the house of Orange, and the heirapparent bears the title of prince of Orange. In November, 1830, the national congress of Belgium declared the house of Orange-Nassau to be forever excluded from all power in Belgium. (See Maurice, William III, William I (prince of Orange), William I (king of the Netherlands), Nassau, and Netherlands.) Orange, the capital of the principality, an old city, known to the Romans under the name of Arausio, contains, at present, 8864 inhabitants. It is situated on the Meyne, in the department of Vaucluse, five leagues north of Avignon.

ORANGEMEN; the name given by the Catholics in Ireland to their Protestant countrymen, on account of their adherence to the house of Orange. Tyrconnel, who had been appointed lord-lieutenant of Ireland by James II (q. v.), attempted to hold the island for his master, and was supported in this design by the Catholics, while the Protestants declared for William. (q. v.) The battle of the Boyne (1690) gave the superiority to the latter, and the Catholics were exposed to the most cruel treatment, in addition to being subjected to heavy civil and religious disabilities. (See Catholic Emancipation.) An attempt has been made to revive the old Orange lodges, in opposition to the Catholic Association, during the present century.

ORATORIO; a musical drama of a dignified character, which is destined only for musical execution, not for theatrical action. Hence, on the part of the poetry, it requires, though not in the strict sense of the theatrical drama, the representation of an action or event, either immediately by the persons concerned in the action or event, or mediately by those who narrate the circumstances, and by the chorus at intervals, in which the whole body of individuals concerned express their feelings in music. The subject should be of a noble character (as, for example, the Creation), and the music adapted to express various elevated and tender affections. Oratorios are generally on religious subjects, particularly biblical histories and events. The oratorio, properly speaking,

commenced when sacred music was distinctly separated from worldly. It had its origin partly in the songs and alternating choruses of the Christian pilgrims, who sung on their pilgrimages, in the time of the crusades, of the life and death of the Redeemer, the last judgment, and other religious subjects, in the streets and public places; and partly in the mysteries, or dramatic representations of sacred narratives. As early as 1243, a spirituale commedia was performed in Padua. St. Philip of Neri (born at Florence, 1515, and died at Rome, in 1595), the founder of the congregation of priests of the oratorio, is regarded as the person who first instituted regular oratorios about the year 1540, in order to direct the fondness for the musical drama to religious subjects. The oratorios were then little more than hymns accompanied by instrumental music, whence they first appeared in Rome under the name of laudi spirituali. The recitative (q. v.), or musical narration, was invented afterwards. At first, however, the oratorios were narratives, rather than dramas, for an actor related the story to the spectators, and detailed the principal points; and only a few musical passages were performed, by which the feeling appropriate to the different situations was expressed. These performances in sacred music obtained the name of oratorios in the middle of the seventeenth century, either from the congregation before spoken of, or from the church where they were executed. Emilio del Cavalieri (about 1590) composed oratorios with recitatives. In the seventeenth century, the oratorio, as well as the opera, became developed in its poetical and musical form. The first oratorios had short choruses, in simple counterpoint; but, in the second half of the seventeenth century, it was customary to conclude with a duet every separate portion of an oratorio, which generally occupied about an hour in the performance. In the beginning of the eighteenth century, Pariati, the Jesuit Ceva, Lel. Orsini, Spagna, Zeno, and Metastasio, wrote oratorios, and Caldara, Jomelli, Leo, Buononcini, composed the music. A more ele vated character was given to the oratorio by Handel, who devoted all his power to the chorus till 1732. Haydn distinguished himself by richness of description, and he introduced worldly subjects and music into the oratorio.-Oratorio signifies, likewise, a place of prayer, especially in monasteries.

ORATORY, PRIESTS OF THE; a religious order founded by Philip Neri (q. v.), in 1574,