Tiberius, was born at Vulsinii in Etruria. He was commander of the praetorian bands, acquired the confidence of Tiberius, and aimed at the supreme power. He contrived to remove all the members of the imperial family who stood between him and power, but having awakened the suspicion of Tiberius he was executed in A. D. 31.
SEL D'OR, a double hyposulphite of gold and sodium, used in photography for toning positive paper-proofs.
SELECTIVE DRAFT LAW, a distinctive name given to the measures passed by the United States Congress in 1917, providing for the drafting of men of military age into the armed forces, for service in the World War. See United States, section, United States in the World War.
SELENITE, a name used by some mineralogists for all species of gypsum, by others applied to the crystallized forms only.
SELENIUM, a non-metallic hexad element occupying an intermediate place between sulphur and tellurium: Symbol Se; at. wt. 79.5. It was discovered by Berzelius in 1817. Though not very abundant in nature, it enters into the composition of many minerals, and has been found in the free state in certain parts of Mexico. It is prepared from cuproplumbic selenide by heating the pulverized ore with hydrochloric acid, igniting the insoluble residue with an equal weight of black flux and dissolving out the selenide of potassium with boiling water. By exposing this solution to the air selenium is deposited as a gray powder. Like sulphur, it occurs in the amorphus and crystalline states. In the former it may be drawn out into ruby-colored threads, and when melted and quickly cooled becomes vitreous with a sp. gr. of 4:3, and nearly insoluble in bisulphide of carbon. In the crystalline condition it forms monoclinic prisms of sp. gr.=4.5-4.7. It boils below a red heat and gives off a deep yellow vapor which condenses in scarlet flowers, and when thoroughly heated burns with a blue flame forming selenious anhydride. It is oxidized and dissolved by nitric acid, yielding selenious acid. It is used in certain electric contrivances on account of the changes its electric resistance undergoes when it is subjected to light.
SELEUCIA, the name of several ancient cities of Asia, situated in Assyria, Margiana, Syria, Mesopotamia, Cilicia, Pamphylia, Pisidia, Caria, and other countries, of which the following are the most important. (1) Seleucia on the Tigris was founded by Seleucus I. of Syria, on the left bank of that river, near its junction with the royal canal of Babylonia, and opposite to the mouth of the Delas (now Diala) river, a little S. of the modern city of Bagdad. Commanding the plains of the Tigris and Euphrates and the principal caravan roads of Assyria and Babylonia, on the confines of which it was situated, and peopled by settlers from various countries of western Asia, it rapidly rose in wealth and splendor, and, eclipsing Babylon, became the capital of that part of Asia, till it was in its turn eclipsed by Ctesiphon, built by the Parthians on the opposite bank of the Tigris. The later wars of the Romans against that people proved destructive to Seleucia. A city of upward of 500,000 inhabitants in the 1st century, in the following it was burned by Trajan and Lucius Aurelius Verus, and captured by Septimius Severus, and in the expedition of Julian against the Persians, in the 4th century, was found deserted. (2) Seleucia Pieria, a strong fortress of northern Syria, also founded by Seleucus I., whose remains were preserved there in a mausoleum, was built at the foot of Mount Pieria, on a rock overhanging the Mediterranean a few miles N. of the mouth of the Orontes, and W. of Antioch, with which it was simultaneously founded, and of which it formed the seaport. It surrendered to Ptolemy III. of Egypt, was recovered by Antiochus the Great, and in the latter period of the Syrian kingdom became independent. Under the Romans it rapidly decayed. Considerable ruins of its harbor, fortifications, and necropolis are still to be seen.
SELEUCIDÆ, a dynasty of kings who succeeded to that portion of the empire of Alexander the Great which embraced the Asiatic provinces, and is generally known as Syria. Seleucus I., surnamed Nicator, the founder of the line, born about 358 B. C., was a general of Alexander the Great, shortly after whose death (323 B. C.) he obtained the satrapy of Babylon. Subsequently Antigonus forced him to withdraw into Egypt (316 B. C.), but having induced Ptolemy, the governor of Egypt, along with Lysimachus and Cassander, to take the field against Antigonus, he was enabled to return to Babylon in 312 B. C. He gradually extended his possessions from the Euphrates to the Indus, assumed the title of king in 306, and latterly acquired Syria and the whole of Asia Minor, but was assassinated in 280 B. C. He is said to have been the most upright of Alexander's successors, and was the founder
