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692 THEOBALD chemistry in Paris under Vauquelin and Four- croy, in 1798 became a teacher of that science in the polytechnic school, in 1804 professor in the college de France and the Sorbonne as succes- sor of Vauquelin, and in 1810 also in the poly- technic school. In the latter year he was elect- ed a member of the academy in place of Four- croy. Charles X. on his accession to the throne made him a baron, and under Louis Philippe he was created a peer in 1832, and in 1838 di- rector of the college de France. He was presi- dent of the society for the encouragement of national industry, and founded a society for the benefit of inventors impoverished by use- ful researches. His most popular work, Traite elementaire de chimie theorique et pratique (4 vols. 8vo, 1813-'16 ; 7th ed., 5 vols., 1836), has been translated into several languages. THEOBALD, Lewis, an English author, born at Sittingbourne, Kent, died in September, 1744. He was an attorney, but did not practise. His tragedy "Electra" appeared in 1714; and in 1717 he contributed to Mist's "Weekly Journal" papers under the title of " The Censor," which provoked attacks from other writers, one of whom was Dennis. He published a pamphlet entitled " Shake- speare Restored, or a Specimen of the many Errors as well committed as unamended by Mr. Pope in his Edition of this Poet, designed not only to correct the said Edition, but to restore the true Reading of Shakespeare in all the Editions ever yet published " (4to, London, 1726). For this Pope made him the hero of the "Dunciad." (See POPE, ALEXANDER, vol. xiii., p. 709.) Theobald then brought out an edition of Shakespeare's works (7 vols. 8vo, 1733), which destroyed the reputation of Pope's edition. Theobald wrote or translated 20 plays, now all forgotten, and also brought on the stage a play entitled "The Double Falsehood, or the Distrest Lovers," the greater part of which he asserted was composed by Shakespeare. He also published a life of Sir Walter Raleigh. THEOCRITUS, a Greek poet, born in Syracuse, who flourished about 270 B. 0. He went to Alexandria, and secured the favor of Ptolemy Philadelphus, but returned to Syracuse during the reign of Hiero II. He wrote in a mixed dialect in which the Doric predominated, and was the creator of pastoral poetry as a depart- ment of literature. There are extant 30 poems, called by the general name of " Idyls," which are attributed to him, and 22 epigrams. He had several imitators, of whom the greatest was Virgil. The first edition, containing only 18 idyls, appeared at Milan probably in 1493, and the Aldine edition in 1495. Among the more important subsequent editions are those of Reiske (2 vols., Leipsic, 1765-'6), Warton (Oxford, 1770), and Paley (Cambridge, 1863). The principal English translations of the poems are those of Creech (London, 1681), Fawkes (1767), Polwhele (1786), Chapman (1836), and Calverly (1869). THEODOLITE THEODOLITE, a surveying instrument for measuring vertical and horizontal angles and taking levels, combining the uses of the ordi- nary transit, the quadrant, and the level. In the American form of the instrument, the tele- scope turns over, and the vertical angles are read on a graduated circle. In the English form the vertical angles are read on a semi- circle beneath the telescope and level ; the telescope cannot therefore turn over, but is reversible. The American form is preferable by reason of the greater facility and precision of the adjustments. In common with all such kinds of instruments, it is made of brass. The principal parts are the vertical circle A and the horizontal circle F, which rests upon the plate II. A magnetic needle also rests upon the horizontal plate, which may be used when de- sired for ascertaining the earth's meridian or the deviation of a line from it. The telescope, Theodolite. B, revolves on a horizontal axis, also the axis of the vertical circle, and which rests upon the supports S S. Beneath the telescope and at- tached to it by adjusting screws is the long spirit level L, with a scale attached for mark- ing the position of the air bubble. The small spirit levels D and E serve to level the horizon- i tal circle. The vertical axis of the instrument