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THEODOLITE 338 THEODORE OF MOPSUESTIA construction and purpose of the two, however, differ, the latter being employed for astronomical purposes, while the theodolite is used for land surveying; but the better instruments of this class may be employed for observing the al- titude of celestial bodies. The vertical circle is not generally, however, of suffi- cient size, nor so graduated as to be available for very accurate astronomical observations. When a point is to be viewed with the telescope, the telescope is moved so that the image of the point coincides vath the intersection of the cross wires. The vertical limb is divided into degrees, and is capable of being read by means of the vernier and the microscope to thirds of a minute. A pair of plates, constituting THEODOLITE at their edge the horizontal limb of the iustrument, are free when undamped, to move independently of each other. The plate carries a magnetic compass and two spirit levels at right angles to each other, by means of which the circle may be brought accurately into the horizontal plane by raising or depressing it by means of the screws. The plate is fur- nished with two verniers, diametrically opposite to each other, the degrees marked on which are read off by the mi- croscope. By the motion of the tele- scope, on the horizontal axis of the ver- tical limb, altitudes and vertical angles can be measured, while, by its motion on the vertical axis, the angular dis- tances between two objects can be ascer- tained by the readings on the horizontal circle. Before using a theodolite, it should be properly adjusted; that is, the different parts should be brought to their proper relative positions. The theodolite is in adjustment when the following condi- tions are fulfilled: (1) When the inter- section of the cross wires is in the axis of the telescope. (2) When the axis of the attached level is parallel to the axis of the telescope. (3) When the axes of the levels on the horizontal limb are per- pendicular to the axis of the horizontal limb. (4) When the axis of the vertical limb is perpendicular to the axis of the horizontal limb. THEODORA, the famous consort of the Byzantine emperor, Justinian I.; was, according to the dubious evidence of Pro- copius, the daughter of Acacius, a bear- ward at Constantinople; and had already been by turns actress, dancer and harlot, when she won the heart of the austere and ambitious Justinian, to become in succession to his mistress, his wife, and the sharer of his throne (527). There was a law which forbade a member of the sen- ate to marry an actress, but Justinian cleared the way by repealing it. Never thereafter did the breath of scandal touch her name; she became Justinian's trustiest counsellor bore a chief share in the work of government, and saved the throne by her high courage at the crisis of the Nika riots (532). She lav- ished her bounty on the poor, and es- pecially on the unfortunate of her own sex, and died at 40 (548), her slender and graceful frame worn out by the anxieties of State. Her character de- scended to history unspotted till the ap- pearance (1623) of the "Secret History" of Procopius, the work of a man who had enjoyed the full favor and confidence of the court, and had in his other writ- ings openly extolled the triumphs and the wisdom of Justiniana and Theodora, whose reputation he was the while la- boring in secret to destroy. His stories satisfied his first editor, Nicholas Ale- mannus, and later Gibbon and Dahn, but other writers have very properly questioned the testimony of Procopius regarding Theodora's profligacy after she became a queen. THEODORE OF MOPSUESTIA, an exegete of the early Church; bom in Antioch about the middle of the 4th cen- tury. He was the friend of Chrysostom and the pupil of Libanius, but it was Dio- dorus of Tarsus from whom he imbibed his zeal for Biblical studies. About the year 383 he became a presbyter in An-