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 suicide on the 27th of June 1791. Merck distinguished himself mainly as a critic; his keen perception, critical perspicacity and refined taste made him a valuable guide to the young writers of the Sturm und Drang. He also wrote a number of small treatises, dealing mostly with literature and art, especially painting, and a few poems, stories, narratives and the like; but they have not much intrinsic importance. Merck’s letters are particularly interesting and instructive, and throw much light upon the literary conditions of his time.

MERCŒUR, SEIGNEURS AND DUKES OF. The estate of Mercœur in Auvergne, France, gave its name to a line of powerful lords, which became extinct in the 14th century, and passed by inheritance to the dauphins of Auvergne, counts of Clermont. In 1426 it passed to the Bourbons by the marriage of Jeanne de Clermont, dauphine of Auvergne, with Louis de Bourbon, count of Montpensier. It formed part of the confiscated estates of the Constable de Bourbon, and was given by Francis I. and Louise of Savoy to Antoine, duke of Lorraine, and his wife, Renée de Bourbon. Nicolas of Lorraine, son of Duke Antoine, was created duke of Mercœur and a peer of France in 1569. His son Philippe Emmanuel (see below) left a daughter, who married the duc de Vendôme in 1609.

MERCŒUR, PHILIPPE EMMANUEL DE LORRAINE, (1558–1602), French soldier, was born on the 9th of September 1558, and married Marie de Luxemburg, duchesse de Penthièvre. In 1582 he was made governor of Brittany by Henry III., who had married his sister. Mercœur put himself at the head of the League in Brittany, and had himself proclaimed protector of the Roman Catholic Church in the province in 1588. Invoking the hereditary rights of his wife, who was a descendant of the dukes of Brittany, he endeavoured to make himself independent in that province, and organized a government at Nantes, calling his son “prince and duke of Brittany.” With the aid of the Spaniards he defeated the duc de Montpensier, whom Henry IV. had sent against him, at Craon in 1592, but the royal troops, reinforced by English contingents, soon recovered the advantage. The king marched against Mercœur in person, and received his submission at Angers on the 20th of March 1598. Mercœur subsequently went to Hungary, where he entered the service of the emperor Rudolph II., and fought against the Turks, taking Stuhlweissenburg (Székes-Fehérvár) in 1599. Mercœur died on the 19th of February 1602.

MERCURY, in Roman mythology, the god of merchandise (merx) and merchants; later identified with the Greek Hermes. His nature is more intelligible and simple than that of any other Roman deity. In the native Italian states no trade existed till the influence of the Greek colonies on the coast introduced Greek customs and terminology. It was no doubt under the rule of the Tarquins that merchants began to ply their trade. Doubtless the merchants practised their religious ceremonies from the first, but their god Mercurius was not officially recognized by the state till the year 495 Rome frequently suffered from scarcity of grain during the unsettled times that followed the expulsion of the Tarquins. Various religious innovations were made to propitiate the gods; in 496 the Greek worship of Demeter, Dionysus and Persephone was established in the city, and in 495 the Greek god Hermes was introduced into Rome under the Italian name of Mercurius (Livy ii. 21, 27), as protector of the grain trade, especially with Sicily. Preller thinks that at the same time the trade in grain was regulated by law and a regular college or gild of merchants instituted. This college was under the protection of the god; its annual festival was on the 15th (the ides) of May, on which day the temple of the god had been dedicated at the southern end of the Circus Maximus, near the Aventine; and the members were called mercuriales as well as mercatores. Mommsen, however, considers the mercuriales to be a purely local gild—the pagani of the Circus valley. The 15th of May was chosen as the feast of Mercury, obviously because Maia was the mother of Hermes, that is of Mercury; and she was worshipped along with her son by the mercuriales on this day. According to Preller, this religious foundation had a political object; it established on a legitimate and sure basis the trade between Rome and the Greek colonies of the coast, whereas formerly this trade had been exposed to the capricious interference of government officials. Like all borrowed religions in Rome, it must have retained the rites and the terminology of its Greek original (Festus p. 257). Mercury became the god, not only of the mercatores and of the grain trade, but of buying and selling in general; and it appears that, at least in the streets where shops were common, little chapels and images of the god were erected. There was a spring dedicated to Mercury between his temple and the Porta Capena; every shopman drew water from this spring on the 15th of May, and sprinkled it with a laurel twig over his head and over his goods, at the same time entreating Mercury to remove from his head and his goods the guilt of all his deceits (Ovid, Fasti, v. 673 seq.). The word mercurialis was popularly used as equivalent to “cheat.”

 MERCURY, in astronomy, the smallest major planet and the nearest to the sun; its symbol is ☿. Its proximity to the sun makes the telescopic study of its physical constitution extremely difficult. The result is that less is known on this subject than in the case of any other planet. Even the time of rotation on its axis is uncertain. J. H. Schröter inferred a period of rotation of 24 h. 5 m. 30 s., which was in seeming agreement with the observations of K. L. Harding. This period was generally accepted, though Herschel had been unable to see any changes indicating rotation. In 1882 G. Schiaparelli began a careful study of the face of the planet with a refractor of 8 in. aperture, subsequently replaced by one of 18 in. His unexpected conclusion was that the rotation of Mercury resembles that of the moon, in having its period equal to that of its orbital revolution. As the moon always presents the same face to the earth, so Mercury must, in this case, always present very nearly the same face to the sun. Schiaparelli also announced that the axis of rotation of the planet is nearly perpendicular to the plane of its orbit. The rotation being uniform, while the orbital motion, owing to the great eccentricity of the orbit, is affected by a very large inequality, it would follow that there is a libration in longitude of nearly 24° on each side of the mean position. Percival Lowell in 1897 took up the question anew by combining a long series of measured diameters of the planet with drawings of its apparent surface. The seeming constancy of the surface appearance was considered to confirm the View of Schiaparelli as to the slow rotation of the planet. But there is wide room for doubt on the question.

The period of orbital revolution of Mercury is nearly 88 days, or somewhat less than three months. Consequently, the period of synodic revolution is less than four months, during which the entire round of phases is completed. When near greatest elongation Mercury shines as a star of the first magnitude, or brighter; but in the latitudes of central and northern Europe it is so near the horizon soon after sunset as to be generally obscured by vapours or clouds.

The eccentricity of the orbit, 0·20, is far greater than that of any major planet, and nearly the average of that of the minor planets. Consequently, its distance and its greatest elongation from the sun vary widely with its position in its orbit at the time.

The mass of Mercury can be determined only from its action upon Venus; this is so small that the result is doubtful. Leverrier adopted in his tables 1:3,000,000 as the ratio of the mass of Mercury to that of the sun. S. Newcomb, from the action upon Venus, reduced this to one-half its amount, or 1:6,000,000.