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THAYER, ABBOTT HANDERSON (1849–1921), American painter and naturalist (see 26.728), died at Dublin, N.H., May 29 1921. During the World War he worked in England on the development of camouflage.

THAYER, WILLIAM ROSCOE (1850–⁠), American writer, was born in Boston, Mass., Jan. 16 1859. He studied at St. Mark’s Academy, Concord, N.H., travelled with a private tutor in Europe, and graduated from Harvard in 1881, in the class with Theodore Roosevelt. For several years he was assistant editor of the Philadelphia Evening Bulletin, then returned to Harvard, receiving the degree of A.M. in 1886. When the Harvard Graduates' Magazine was established in 1892 he was appointed editor, serving until 1915. In 1903, at the International Historical Congress at Rome, he represented both Harvard University and the American Historical Association, and in 1906 was their representative at the Italian Historical Congress in Milan. He was a member of the Harvard Board of Overseers from 1913 to 1919. In 1902 he was made Knight of the Order of the Crown of Italy, and in 1917 Knight of the Order of Saints Maurizio and Lazaro. In 1918 he was elected president of the American Historical Association. He was best known for his works on Italian history, especially The Dawn of Italian Independence 1814 to 1840, 2 vols. (1893) ; A Short History of Venice (1905), and The Life and Times of Cavour, 2 vols. (1911). His other works include Italica (1908); The Life and Letters of John Hay, 2 vols. (1915); Letters of John Holmes (1917); Theodore Roosevelt—An Intimate Biography (1918); Democracy: Discipline: Peace (1919, lectures at Brown University); Volleys From a Non-Combatant (1919); and The Art of Biography (1920, lectures at the university of Virginia).

THEAL, GEORGE McCALL (1837–1919), British historiographer, was born in Canada, where his family had long been settled. When 19 he went to Sierra Leone, removing two years later to Cape Colony, where he became a schoolmaster. He quickly developed an interest in the natives and in the history of the country. In 1877, on behalf of the Government he settled a dispute with the Gaika Kaffirs, and thereafter joined the Cape Civil Service, being attached to the Native Department. Shortly afterwards he was also appointed Keeper of the Archives, and in 1891 was made Colonial Historiographer, which position he held until 1905. Before joining the Civil Service he had published in one volume a History of South Africa and the first fruits of his Bantu studies were embodied in Kaffir Folk Lore (1882). From the time he obtained access to the Cape archives he devoted himself to research. In 1895 he was commissioned by Cecil Rhodes, then Prime Minister of Cape Colony, to go to Europe, where he stayed several years examining the Portuguese archives at Lisbon, the Dutch archives at The Hague and the British in London. He constantly enlarged and revised his History which in its final form was in eleven volumes, the first dealing with ethnography and conditions up to 1505, the others carrying on the story of S. Africa up to 1884. Theal also published official Records of the Cape Colony, 1793–1827, in 36 slim volumes, Records of South East Africa in nine volumes, and many other works, some in Dutch.

Theal'’ industry never flagged. He died at Wynberg, Cape Province, on April 17 1919, in the act of correcting the proofs of the last two volumes of his history. The founder of what may be called the Dominions school of historians, he was himself a chronicler rather than an historian. His passion for research brought to light a mass of unknown or forgotten documents of high value, but his narrative is overloaded with details, is essentially domestic, and not always impartial. He lacked the wider vision which sees events in their true perspective. Theal was given the honorary degree of Litt.D. by the Cape University in 1899; he had previously been made an hon. LL.D. of Queen’s University, Kingston, Canada.

THERMIT, AND THERMIT WELDING.—Thermit is a mixture of aluminium powder and iron oxide. On ignition the reaction, 8Al+3Fe₃O₄ = 9Fe+4Al₂O₂, gives a temperature estimated to be between 2,300 and 2,700°C. The reaction, stated in weights, means that 217 parts of aluminium plus 732 parts magnetite (iron oxide) equals 540 parts steel plus 409 parts slag, or approximately 3 parts of aluminium plus to parts of magnetite wil produce, on combustion, 7 parts of steel. This steel represent: about one-half of the original thermit by weight and one-third by volume.

Thermit was discovered by Dr. Hans Goldschmidt of Essen Germany, in 1895, while trying to reduce chromium and manganese. Dr. Goldschmidt’s principal discovery related to simple and safe method of ignition, as the action of aluminium when mixed with various oxides, sulphides, and chlorides was well known. Fine aluminium will not burn below the tempera inn of molten cast iron, and previous experimenters had resorted to heating their mixtures in a crucible. This made the initial temperature so high at the moment of ignition that there was an explosion. Dr. Goldschmidt obtained ignition of a cold mixture by means of a barium-peroxide fuse, which was set off by a storm match. Later magnesium powder or ribbon was used, being set off in the same way. A red-hot iron rod may also be used to set off the magnesium, which in turn ignites the thermit. Dr. Goldschmidt’s original American patent No. 615,700 was granted March 16 1897, and related principally to the use of aluminium as a reducing agent for the production of carbon-free metals such as cobalt, chromium, magnesium, tungsten, etc., by what is now known as the aluminothermic process.

Thermit is now used considerably in the foundry for purifying iron and steel in the ladle. For this purpose the thermit is placed in a can on the end of a rod and plunged to the bottom of the molten metal. The intense heat generated tends to liberate many impurities which are carried away in the slag. The principal and better-known use, however, is in welding.

THERMIT WELDING. Two methods are employed, known as the plastic and the fusion. The first is used for welding pipe and the latter for solid or large sections. In the plastic method, in which the

Fig. 1. Showing the action of Thermit when poured into a pipe welding mould.

thermit is used merely for heating purposes, the ends of two pieces of pipe are machined square and clamped in a cast-iron mould with the ends butted together. This mould is in two parts, so arranged that the pipe ends may be forced together when heated. The thermit is placed in an open-top crucible lined with magnesia-tar, and ignited. After the reaction takes place the slag rises to the top of the molten metal, and is first poured into the mould as shown at the

Fig. 2. Tapping a crucible showing a partial sectional view.

left in fig. I. This slag forms a protective coating on the pipe and on the inside of the mould, and keeps the thermit from melting or burning through. At the right the thermit is shown flowing into the