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staff. Most theodolites have no telescopes, but only four plainsights, two of them fastened on the limb, and tvyo on the ends ofthe index. Mr. Sisson’s improved theodolite being one of the■best of these instruments, we shall here give its description. Thethree staves, whereby it is supported, screw into bell-metal-jointsby brass-ferrils at top, which are moveable between brass-pillars■fixed in a strong brass-plate; in which, round the centre, is fixeda socket with a ball moveable in it, and upon which the fourscrews press that set the limb horizontal. Next above is such an-other plate, through which the said screws pass, and on which,r.oend the centre, is fixed the frustum of a cone of bell-metal,whose axis, being connected with the centre of the ball, is alwaysperpendicular to the limb, by means of a conical brass-ferril fittedto it, whereon is fixed the compass-box, and on it the limb, w hichis a strong hell-metal-ring, whereon are moveable three brass in-dexes, in whose plate are fixed four brass-pillars, that joining attop, hold the centre-pin of the bell-metal double sextant, whosedouble index is fixed in the centre of the same plate. Within thedouble sextant is fixed the spirit-level, and over it the telescope.See Level. The compass-box is graved with two diamonds fornorth and south, and with twenty degrees on both sides of each,that the needle may be set to the variation, and its error alsoknown. The limb has two fleur-de-luces against the diamonds inthe box, and is curiously-divided into whole degrees, and num-bered to the left-hand at every 10° to twice 180°, having three in-dexes (with Nonius’s divisions on each for the decimals of a de-gree) that are moved by a pinion fixed below one of them withoutmoving the limb, and in another is a screw and spring under, tofi* it to any part of the limb : it has also divisions numbered fortaking the quarter girt in round timber; to which a shorter indexis used, having Nonius’s divisions for the decimals of an inch ; butan abatement must be made for the bark, if it be not taken off. SeeRule. The double sextant is divided on one side from under itscentre (when the spirit-tube and telescope are level) to above sixtydegrees each way, and numbered at 10, 20, &c. And the doubleindex (through which it is moveable) shews on the same side thedegree and decimal of any altitude or depression to that extent,By Nonius’s divisions; on the other side are divisions numberedfor taking the upright height of timber, &c. in feet, when distantten feet, which at twenty must be doubled, and at 30 trebled ;and also the quantities for reducing hypothenusal lines to horizon-tal : it is moveable by a pinion fixed in the double index. T lietelescope is a little shorter than the diameter of the limb, that afall may not hurt it; yet it will magnify as much, and shew a dis-tinct object as perfect, as most of treble its length: in its focus arevery fine cross-wires, whose intersection is in the plane of the dou-ble sextant, and this was a whole circle, and turned in a lathe to atrue plane, and is fixed at right-angles to the limb ; so that when-ever the limb is set horizontal (which is readily done by makingthe spirit tube level over two screws, and the like over the othertwo) the double sextant and telescope are moveable in a verticalplane, and then every angle taken on the limb (though the tele-scope lie never so much elevated or depressed) will lie an angle inthe plane of the horizon, and this is ablolutely necessary in theplotting an horizontal plane.

THEODORET, bishop of St. Cyricus in Syria , in the fourthcentury, and one of the most learned fathers of the church, wasborn A. D. 386, and was the disciple of Theodorus of Mopsuestesand St. John Chrysostom . Having received holy orders, he waswith difficulty persuaded to accept of the bishopric of St. Cyricus,about A. D. 420. lie displayed great frugality in the expelleesof his table, dress, and furniture, hut spent considerable sums inimproving and adorning the city of Cyricus. Yet his zeal was notconfined to his own church : lie went to preach at Antiocli andthe neighbouring towns; where lie became admired for his elo-quence and learning, and had the happiness to convert multitudesof people. He wrote in favour of John of Antioch and the Nesto-rians, against Cyril’s Twelve Anathemas, he afterwards attackedtlie opinions of Nestorius , and was deposed in the synod held bythe Eutychinns at Ephesus ; but was again restored by the generalcouncil of Chalcetlon, in which lie was present, in 451. It isthought that he died soon after; though others says that lie livedtill A. D. 457. There are still extant Theodoret ’s excellentCommentaries on St. Paul’s Epistles, and on several other booksof the Holy Scriptures. 2. His Ecclesiastical History from thetime of Arius to Theodosius the Younger. 3. History of the An-chorites. 4. Epistles. 5. Discourses on Providence. 6. A Trea-tise intituled, De Curandis Gracorum Affectibus;* and oilierworks. The best edition is that of Sirniond, in Greek and Latin ,in 4 vols. folio.

THEODORUS, bishop of Mopsuestes, a city in Cilicia , alearned prelate of the fifth century. He wrote a Commentary onthe Psalms; another on the twelve minor prophets; which, withsome other fragments, are extant. He died A. D. 428. But hisworks were condemned in the fifth general council, as favouringNestorinuhm.

THEODOSIUS , a celebrated mathematician, who flourishedin the times of Cicero and Pompey ; but the time and place of hisdeath are unknown. Theodosius chiefly cultivated that part ofgeometry which relates to the doctrine of the sphere, concerningwhich he published three books, of which a good English transla-tion was made by Dr. Barrow.

TH EODO PUS, a native of Byzantium, who flourished in thereign of Marcus Aurelius, and at first professed Christianity , butduring the persecution under that emperor, renounced it, and af-terwards set up a new heresy, called from him Theodotian, orTlieodosian. See Thf.odosians. He was a tanner by pro-fession.

THEOGNIS, an ancient Greek poet of Megare, in Achaia,who flourished about the 5<Jtli Olympiad, 144 B. C. We have awork of liis extant, concerning a summary of precepts and reflec-tions, usually to be found in the collections of the Greek minorpoets.

THEOGONY, [from ©«;, God , and yov>i genitura, seed oroffspring,] Hesiod gives us the ancient theogony, in a poem underthat title. Among the most ancient writers, Dr. Burnet observes,that theogony and cosmogony signified the same thing. In effect,the generation of the gods of the ancient Persians , fire, water, andearth, is apparently no other than that of the primary elements.

THEOLOGY.

THEOLOGY, or DFVINITY, [$«xoyi«,] is that sciencewhich treats of the being and attributes of God , his relations to us,the dispensations of his providence, his will with respect to our ac-tions, and his purposes with respect to our end. The word wasfirst used to denote the systems of those poets and philosopherswho w rote of the genealogy and exploits of the gods of Greece .HenceOrpheus, Museus, Hesiod, Plierecydes, and Pythagoras ,were called theologians; as was Plato , on account of his specula-tions on the same subject. It was afterwards adopted by the ear-liest writers of the Christian church, w ho styled the author of theApocalypse, by way of eminence, j 9n>xoyoc, the Divine. Theo-logy has God , and the things lie has revealed, for its object..Hence theology may be distinguished into natural, which com*

prebends the knowledge we have of God from his works, by thelight of reason alone; and supernatural, which contains what weare taught concerning God in revelation. Concerning the extentof natural theology many opinions have been formed; but intothese disputes we mean not to enter. It is undeniable that thereare some of the principles of theology which may be called natu*ral; for though it is probable that tiie parents of mankind receivedall their theological knowledge by supernatural means, it is yetobvious that some parts of that knowledge must have been capa-ble of a proof purely rational, otherwise not a single religioustruth could have been conveyed through the succeeding genera-tions of the human race by the immediate inspiration of eachindividual. We indeed admit many propositions as certainly true,