MERCURY, in astronomy, the planet nearest the sun. Its stationary points are from 15 to 20 degrees of longitude from the sun, hence it rises and sets not far from the time when the sun does so. The light of the sun and the haze of the horizon combine to render observation of the planet difficult. It varies in bright ness from 15" to 12" of the celestial circle or vault. Hence it is sometimes telescopic, and at other times visible to the naked eye, being as bright as a star of the second magnitude. It was known to the ancients. Its diameter is about 3, 200 miles; its mass about 1-19 that of the earth; its sidereal period is 88 terrestrial days. It is seen at its greatest bright ness as an evening star, at average inter vals of about 116 days. Its average dis tance from the sun is 36,000,000 miles. The orbit of Mercury is remarkable for its extreme eccentricity, the distance from the sun varying periodically from about 28,500,000 to 48,500,000 miles.
In Chemistry.—A diatomic metallic ele ment; symbol, Hg; at. wt., 200; sp. gr., 13.59; boiling point, 357.25; known from
the earliest historical times, and the only liquid metal at ordinary temperatures. It is found most frequently in the form of merctiric sulphide, or cinnabar, an ore found in Spain, Austria, and other parts of the world, from which it is extracted by roasting the ore in a furnace, and conducting the vapors into a chamber where the mercury is condensed, while the sulphurous acid is allowed to escape. It possesses a luster like that of polished silver, and solidifies at-39.5° to a tin white malleable mass, contracting at the moment of solidification.
In Classical Mythology.—A Roman deity, identified with the Greek Hermes. He was the son of Jupiter and Maia. He was the messenger and herald of the gods, and as such he was represented as a youth, lightly clad, with the petasus or winged hat, and wings on his heels, bear ing in his hand the caduceus or emblem of his office as a herald, a rod with two serpents twined round about it.