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 DUHAMEL, JEAN BAPTISTE (1624–1706), French physicist, was born in 1624 at Vire in Normandy. He studied at Caen and Paris; wrote at eighteen a tract on the Spherics of Theodosius of Tripolis; then became an Oratorian priest, and fulfilled with great devotion for ten years (1653–1663) the duties of curé at Neuilly-sur-Marne. He was appointed in 1656 almoner to the king, and in 1666 perpetual secretary to the newly founded Academy of Sciences. He died on the 6th of August 1706. He published among other works: Astronomia physica (1660) and De meteoris et fossilibus (1660), both in dialogue form; De consensu veteris et novae philosophiae (1663); De corporum affectionibus (1672); De mente humana (1673); Regiae scientiarum Academiae historia, 1666–1696 (1698), new edition brought down to 1700 (1701); Institutiones biblicae (1698); followed by annotated editions of the Psalms (1701), of the Book of Wisdom, &c. (1703), and of the entire Bible in 1705.

 DUHAMEL DU MONCEAU, HENRI LOUIS (1700–1782), French botanist and engineer, son of Alexandre Duhamel, lord of Denainvilliers, was born at Paris in 1700. Having been requested by the Academy of Sciences to investigate a disease which was destroying the saffron plant in Gâtinais, he discovered the cause in a parasitical fungus which attached itself to the roots, and this achievement gained him admission to the Academy in 1728. From then until his death he busied himself chiefly with making experiments in vegetable physiology. Having learned from Sir Hans Sloane that madder possesses the property of giving colour to the bones, he fed animals successively on food mixed and unmixed with madder; and he found that their bones in general exhibited concentric strata of red and white, whilst the softer parts showed in the meantime signs of having been progressively extended. From a number of experiments he was led to believe himself able to explain the growth of bones, and to demonstrate a parallel between the manner of their growth and that of trees. Along with the naturalist Buffon, he made numerous experiments on the growth and strength of wood, and experimented also on the growth of the mistletoe, on layer planting, on smut in corn, &c. He was probably the first, in 1736, to distinguish clearly between the alkalis, potash and soda. From the year 1740 he made meteorological observations, and kept records of the influence of the weather on agricultural production. For many years he was inspector-general of marine, and applied his scientific acquirements to the improvement of naval construction. He died at Paris on the 13th of August 1782.

 DÜHRING, EUGEN KARL (1833–1901), German philosopher and political economist, was born on the 12th of January 1833 at Berlin. After a legal education he practised at Berlin as a lawyer till 1859. A weakness of the eyes, ending in total blindness, occasioned his taking up the studies with which his name is now connected. In 1864 he became docent of the university of Berlin, but, in consequence of a quarrel with the professoriate, was deprived of his licence to teach in 1874. Among his works are Kapital und Arbeit (1865); Der Wert des Lebens (1865); Natürliche Dialektik (1865); Kritische Geschichte der Philosophie (1869); Kritische Geschichte der allgemeinen Principien der Mechanik (1872)—one of his most successful works; Kursus der National- und Sozialökonomie (1873); Kursus der Philosophie (1875), entitled in a later edition Wirklichkeitsphilosophie; Logik und Wissenschaftstheorie (1878); Der Ersatz der Religion durch Vollkommeneres (1883). He published his autobiography in 1882 under the title Sache, Leben und Feinde; the mention of “Feinde” (enemies) is characteristic. Dühring’s philosophy claims to be emphatically the philosophy of reality. He is passionate in his denunciation of everything which, like mysticism, tries to veil reality. He is almost Lucretian in his anger against religion which would withdraw the secret of the universe from our direct gaze. His “substitute for religion” is a doctrine in many points akin to Comte and Feuerbach, the former of whom he resembles in his sentimentalism. Dühring’s opinions changed considerably after his first appearance as a writer. His earlier work, Natürliche Dialektik, in form and matter not the worst of his writings, is entirely in the spirit of the Critical Philosophy. Later, in his movement towards Positivism, he strongly repudiates Kant’s separation of phenomenon from noumenon, and affirms that our intellect is capable of grasping the whole reality. This adequacy of thought to things is due to the fact that the universe contains but one reality, i.e. matter. It is to matter that we must look for the explanation both of conscious and of physical states. But matter is not, in his system, to be understood with the common meaning, but with a deeper sense as the substratum of all conscious and physical existence; and thus the laws of being are identified with the laws of thought. In this materialistic or quasi-materialistic system Dühring finds room for teleology; the end of Nature, he holds, is the production of a race of conscious beings. From his belief in teleology he is not deterred by the enigma of pain; he is a determined optimist. Pain exists to throw pleasure into conscious relief. In ethics Dühring follows Comte in making sympathy the foundation of morality. In political philosophy he teaches an ethical communism, and attacks the Darwinian principle of struggle for existence. In economics he is best known by his vindication of the American writer H. C. Carey, who attracts him both by his theory of value, which suggests an ultimate harmony of the interests of capitalist and labourer, and also by his doctrine of “national” political economy, which advocates protection on the ground that the morals and culture of a people are promoted by having its whole system of industry complete within its own borders. His patriotism is fervent, but narrow and exclusive. He idolized Frederick the Great, and denounced Jews, Greeks, and the cosmopolitan Goethe. Dühring’s clear, incisive writing is disfigured by arrogance and ill-temper, failings which may be extenuated on the ground of his physical affliction. He died in 1901.

 DUIGENAN, PATRICK (1735–1816), Irish lawyer and politician, was the son of a Leitrim Roman Catholic farmer named O’Duibhgeannain. Through the tuition of the local Protestant clergyman, who was interested in the boy, he got a scholarship in 1756 at Trinity College, Dublin, and subsequently became a fellow. He was called to the Irish bar in 1767 and obtained a rich practice. He is remembered, however, mainly as a politician, on account of his opposition to Grattan, his support of the Union, and his violent antagonism to Catholic emancipation. He was elected member for Armagh in the first united parliament, and was a well-known character at Westminster till he died on the 11th of April 1816.

 DUIKER (diver), or, the Dutch name of a small S. African antelope, scientifically known as Cephalophus grimmi; the popular name alluding to its habit of diving into and threading its way through thick bush. Scientifically the name is extended to include all the members of the African genus Cephalophus, which, together with the Indian chousingha, or four-horned antelope (Tetraceros), constitutes the subfamily Cephalophinae. Duikers are animals of small or medium size, usually frequenting thick forest. The horns, usually present in both sexes, are small and straight, situated far back on the forehead; and between them rises the crest-like tuft of hair from which the genus takes its scientific name. The common or true duiker (C. grimmi) is found in bush-country from the Cape to the Zambezi and Nyasaland, and ranges northward on the west coast to Angola. The banded duiker (C. doriae) from West Africa is golden brown with black transverse bands on the back and loins. C. sylvicultor, of West Africa, is the largest species, and approaches a donkey in size. (See .)

 DUILIUS (or ), GAIUS, Roman general during the first Carthaginian War and commander in the first Roman naval