or Magnesia, in Ancient Geography, a town or a district of Thessaly, at the foot of Mount Pelius, called by Philip, the son of Demetrius, one of the three keys of Greece, (Pausanias).

or Magnesia alba, in Chemistry, a peculiar kind of earth. See Chemistry Index.

Black MAGNESIA. See Manganese, Chemistry and Mineralogy Index.

Ancient Geography, a maritime district of Thessaly, lying between the south part of the Sinus Thermaicus and the Pegasus to the south, and to the east of the Pelasgians. Magnetes, the people. Magnesias and Magnesius, the epithet; (Horace).

town of Asia Minor on the Maeander, about 15 miles from Ephesus. Themistocles died there: it was one of the three towns given him by Artaxerxes, with these words, "to furnish his table with bread." It is also celebrated for a battle which was fought there, 190 years before the Christian era, between the Romans and Antiochus king of Syria. The forces of Antiochus amounted to 70,000 men according to Appian, or 70,000 foot and 12,000 horse according to Livy, which has been exaggerated by Florus to 300,000 men; the Roman army consisted of about 28,000 or 30,000 men, 2000 of whom were employed in guarding the camp. The Syrians lost 50,000 foot and 4000 horse; and the Romans only 300 killed, with 25 horse. It was founded by a colony from Magnesia in Thessaly; and was commonly called Magnesia ad Maeandrum, to distinguish it from another called Magnesia ad Sipylum in Lydia at the foot of Mount Sipylus.

Magnesia ad Sipylum, anciently Tantalis, the residence of Tantalus, and capital of Maeonia, where now stands the lake Sale. A town of Lydia, at the foot of Mount Sipylus, to the east of the Hermus; adjudged free under the Romans. It was destroyed by an earthquake in the reign of Tiberius.

Magnet (Magnes) the Loadstone; a species of iron ore. See Magnetism, and Mineralogy Index.

The magnet is also called Lapis Heraeetus, from Heraeica, a city of Magnesia, a port of the ancient Lydia, where it is said to have been first found, and from which it is usually supposed to have taken its name. Though others derive the word from a shepherd named Magnes, who first discovered it with the iron of his crook on Mount Ida. It is also called Lapis Nauticus, from its use in navigation; and siderrites, from its attracting iron, which the Greeks call σιδήρες.

The ancients reckoned five kinds of magnets, different in colour and virtue; the Ethiopic, Magnesian, Boeotic, Alexandrian, and Natolian. They also took it to be male and female: but the chief use they made of it was in medicine; especially for the cure of burns and defluxions on the eyes.—The moderns, more fortunate in its application, employ it to conduct them in their voyages. See Navigation.

The most distinguished properties of the magnet are, That it attracts iron, and that it points to the poles of the world; and in other circumstances also dips or inclines Magnet. clings to a point beneath the horizon, directly under the pole; and that it communicates these properties, by touch, to iron. On which foundation are built the mariner's needles, both horizontal and inclinatory.

Attractive Power of the Magnet was known to the ancients; and is mentioned even by Plato and Euripides, who call it the Herculean stone, because it commands iron, which subdues every thing else; but the knowledge of its directive power, whereby it disposes its poles along the meridian of every place, and occasional needles, pieces of iron, &c., touched with it, to point nearly north and south, is of a much later date; though the exact time of its discovery, and the discoverer himself, are yet in the dark. The first mention we have of it is in 1265, when Marco Polo the Venetian is said by some to have introduced the mariner's compass; though not as an invention of his own, but as derived from the Chinese, who are said to have had the use of it long before; though some imagine that the Chinese rather borrowed it from the Europeans.

Flavio de Gioia, a Neapolitan, who lived in the 13th century, is the person usually supposed to have the best title to the discovery; and yet Sir G. Wheeler mentions, that he had seen a book of astronomy much older, which supposed the use of the needle; though not as applied to the uses of navigation, but of astronomy. And in Guyot de Provins, an old French poet, who wrote about the year 1180, there is express mention made of the loadstone and the compass, and their use in navigation obliquely hinted at.

The Variation of the Magnet, or its declination from the pole, was first discovered by Seb. Cabot, a Venetian, in 1500; and the variation of that variation, by Mr Gellibrand, an Englishman, about the year 1625. See Variation.

Lastly, The dip or inclination of the needle, when at liberty to play vertically, to a point beneath the horizon, was first discovered by another of our countrymen, Mr R. Norman, about the year 1576. See the article Dipping Needle.