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* THOMSON. 245 THORACIC DUCT. ciety (1812) ; Outlines of Mineralogy and Geol- ogy (1830). THOMSON, William, first Baron Kelvin (1824 — ). An English mathematician and phj-s- ieist, born at Belfast. He graduated in 1843 from Saint Peter's College, Cambridge, and short- ly afterwards was elected to a fellowship. He became professor of natural philosophy in the University of Glasgow in 1846, in which position he continued until 1809. 'hile an undergradu- ate he published a paper On the Uniform Motion of Hint in Homogeneous Solid Bodies and Its Conneetion u-ith the Mathemutienl Theory of Eleetricity, which was favorably received by sci- entists. He was for some time editor of th.? Cambridge Mathematical Journal and was the first editor of the Cambridge and Dublin Mathe- matical Journal which succeeded it, some of his most brilliant discoveries having appeared in these journals. He also contributed to the Comptes Rendus, the Transactions and, Proceed- ings of the Royal Societies of London and Edin- burgh, and various other journals. In the mathe- matical theories of elasticity, vortex-motion, heat, electricity, and magnetism, he made remarkable discoveries. Lord Kelvin was the electrical en- gineer for the Atlantic cables of lS.")7-58 and 1805-06, and made many improvements in sig- naling apparatus and theoretical observations of the greatest value. He invented the mirror galvanometer used for cable signaling, and then devised the siphon recorder still in use for re- ceiving the signals. He also studied the proper- ties of the cable, and his observation that a limit to the speed of operation would early be reached owing to the effect of the statical capacity has been liorne out in a half century of practice. Lord Kelvin acted as engineer for several other cable companies and has invented many pieces of electrical apparatus and methods for measure- ment. He also developed an improved form of mariners' compass which is free from the mag- netic action of the iron of the ship, and a deep- sea sounding apparatus, both of which are in widespread use. Lord Kelvin's work in thermo- dynamics is also of the greatest value. It was he who first apjireciated the importance of the doctrine of the con^^ervation of energy as enunci- ated by Joule and who developed Carnot's work on heat so that it would harmonize with th-:; new theory then being generally accepted. A paper On an Absolute Thermometrie Scale con- tains much that is now considered fundamental in thermodynamics. Lord Kelvin's many scien- tific papers, contributed to various scientific jour- nals, have been collected in book form as follows: Electrostatics and Magnetism, I vol.; Mathe- matical and Physical Papers, 3 vols.: and Popu- lar Lectures and Addresses. 3 vols. In conjunc- tion with Professor P. G. Tait, Lord Kelvin is the author of .1 Treatise on Natural Philosophy. He received many honors from scientific societies, universities and governments, and is a member of the most important academies and learned organizations of Europe an 1 America. Lord Kel- vin visited America in 1884. and after attend- ing the meeting of the British Associa- tion in Montreal, he visited Baltimore and delivered a course of lectures before the Johns Hopkins L'niversity, published under the title Baltimore Lectures. In 1897 he at- tended the Toronto meeting of the British -Vssociation and visited several of the lead- ing universities of the LTnited States. He came once more in 1902. For his work in con- nection with the Atlantic cable he was knighted in 1806, and in 1892 he was raised to the peer- age. Four years later ho celebrated his jubilee as professor of natural philosophy at (ilasgow. Lonl Kelvin may be said to represent the highest type of physicist, since he combines the powers of nuithc- inatical reasoning with the inventive fa<-ulty and manipulative skill of the experimentalist. THOMSON, William McClure (1806-94). A Presbyterian missionary and writer. He was born in Springfield, Ohio, and graduated at Mi- ami College. 1820: studied at Princeton Theolog- ical Seminary: and went as a missionary of the American Board to Syria and Palestine, 1832. The next year he went to Beirut and there re- sided till his return to America, 1877. His repu- tation rests upon his familiar work. The Land and the Book, Biblical Illustrations Drawn from the Mantiers aiirf Customs, the Scenes and the. Scenery of the Holy Land (1859; 2d ed. 1880-85). THOMSON EFFECT. A thermal effect in an electric circuit where the temperature of the wire carrying the current varies from point to point. When the current is flowing in one direction along such a conductor, beat will be liberated at a given point, whereas if the current is reversed the heat at this point will be ab- sorbed. The relative direction of the current and the absorption or liberation of heat depend upon the metal. In the case of iron the current pass- ing from the hot to the cold portion absorbs heat, making the cold part cooler, while in the case of copper this takes place when the current flows from the cold portion to the hot. If the current is reversed, heat will be liberated under these circumstances. See Thermo-Electricitt. THOR, thor. In Scandinavian mythology, the god of thunder. He was the son of Odin and Frigga, while his wife was Sif, or Love. His palace, where he received the warriors who had fallen in battle, was called Bilskirnir. Thunder was caused by the rolling of his chariot, which was drawn by he-goats. He was in the vigor of youth, had a red beard, and was the strong- est of all the gods. He was a terror to the giants, with whom he was perpetually at strife, and whom he struck down with his hammer ISIjolnir. or the smasher, which returned to his hand after being hurled. In the contest at the twilight of the gods, Thor slew the serpent of Midgard, but fell at the same time poisoned by the venom ex- haled from its mouth. The name of Thor was widespread. The Saxons worshiped him as Thu- nar, and Torden. the wrathful deity dreaded by the Lapps, is evidently the Scandinavian Thor. The Gallic god Tarannis. or Tanarus, appears also to be indentical. Of all the .Fsir (q.v.), Thor had unquestionably the most worshipers. In Norway he was the national god. and there, as in Iceland, temples were almost exclusively erected to him. Offerings were made to him. par- ticularly in times of pestilence. Thursday was named for him. The heathen Scandinavians marked their rune-stones with the sign of the hammer of Thor. See Ragnarok; Scandina- vian AXi) Teutonic Mythology. THORACIC DUCT ( from Lat. thorax, from Gk. OQpai, breastplate, part of the body covered