It does not come into existence by the gradual accumulation of water in an impervious basin.
Authorities.—For Dew, see the two essays by Dr Charles Wells (London, 1818), also “An Essay on Dew,” edited by Casella (London, 1866), Longmans', with additions by Strachan; Melloni, Pogg. Ann. lxxi. pp. 416, 424 and lxxiii. p. 467; Jamin, “Compléments à la théorie de la rosée,” Journal de physique, viii. p. 41; J. Aitken, on “Dew,” Trans. Roy. Soc. of Edinburgh, xxxiii., part i. 2, and “Nature,” vol. xxxiii. p. 256; C. Tomlinson, “Remarks on a new Theory of Dew,” Phil. Mag. (1886), 5th series, vol. 21, p. 483 and vol. 22, p. 270; Russell, Nature, vol 47, p. 210; also Met. Zeit. (1893), p. 390; Homén, Bodenphysikalische und meteorologische Beobachtungen (Berlin, 1894), iii.; Taubildung, p. 88, &c.; Rubenson, “Die Temperatur-und Feuchtigkeitsverhältnisse in den unteren Luftschichten bei der Taubildung,” Met. Zeit. xi. (1876), p. 65; H. E. Hamberg, “Température et humidité de l'air à différentes hauteurs à Upsal,” Soc. R. des sciences d’Upsal (1876); review in Met. Zeit. xii. (1877), p. 105.
For Dew Ponds, see Stephen Hales, Statical Essays, vol. i., experiment xix., pp. 52-57 (2nd ed., London, 1731); Gilbert White, Natural History and Antiquities of Selborne, letter xxix. (London, 1789); Dr C. Wells, An Essay on Dew (London, 1818, 1821 and 1866); Rev. J. C. Clutterbuck, “Prize Essay on Water Supply,” Journ. Roy. Agric. Soc., 2nd series, vol. i. pp. 271-287 (1865); Field and Symons, “Evaporation from the Surface of Water,” Brit. Assoc. Rep. (1869), sect., pp. 25, 26; J. Lucas, “Hydrogeology: One of the Developments of Modern Practical Geology,” Trans. Inst. Surveyors, vol. ix. pp. 153-232 (1877); H. P. Slade, “A Short Practical Treatise on Dew Ponds” (London, 1877); Clement Reid, “The Natural History of Isolated Ponds,” Trans. Norfolk and Norwich Naturalists’ Society, vol. v. pp. 272-286 (1892); Professor G. S. Brady, On the Nature and Origin of Freshwater Faunas (1899); Professor L. C. Miall, “Dew Ponds,” Reports of the British Association (Bradford Meeting, 1900), pp. 579-585; A. J. and G. Hubbard, “Neolithic Dewponds and Cattle-Ways” (London, 1904, 1907). (W. N. S.)
DEWAN or Diwan, an Oriental term for finance minister. The word is derived from the Arabian diwan, and is commonly used in India to denote a minister of the Mogul government, or in modern days the prime minister of a native state. It was in the former sense that the grant of the dewanny to the East India Company in 1765 became the foundation of the British empire in India.
DEWAR, SIR JAMES (1842–), British chemist and physicist, was born at Kincardine-on-Forth, Scotland, on the 20th of September 1842. He was educated at Dollar Academy and Edinburgh University, being at the latter first a pupil, and afterwards the assistant, of Lord Playfair, then professor of chemistry; he also studied under Kekulé at Ghent. In 1875 he was elected Jacksonian professor of natural experimental philosophy at Cambridge, becoming a fellow of Peterhouse, and in 1877 he succeeded Dr J. H. Gladstone as Fullerian professor of chemistry in the Royal Institution, London. He was president of the Chemical Society in 1897, and of the British Association in 1902, served on the Balfour Commission on London Water Supply (1893–1894), and as a member of the Committee on Explosives (1888–1891) invented cordite jointly with Sir Frederick Abel. His scientific work covers a wide field. Of his earlier papers, some deal with questions of organic chemistry, others with Graham’s hydrogenium and its physical constants, others with high temperatures, e.g. the temperature of the sun and of the electric spark, others again with electro-photometry and the chemistry of the electric arc. With Professor J. G. M‘Kendrick, of Glasgow, he investigated the physiological action of light, and examined the changes which take place in the electrical condition of the retina under its influence. With Professor G. D. Liveing, one of his colleagues at Cambridge, he began in 1878 a long series of spectroscopic observations, the later of which were devoted to the spectroscopic examination of various gaseous constituents separated from atmospheric air by the aid of low temperatures; and he was joined by Professor J. A. Fleming, of University College, London, in the investigation of the electrical behaviour of substances cooled to very low temperatures. His name is most widely known in connexion with his work on the liquefaction of the so-called permanent gases and his researches at temperatures approaching the zero of absolute temperature. His interest in this branch of inquiry dates back at least as far as 1874, when he discussed the “Latent Heat of Liquid Gases” before the British Association. In 1878 he devoted a Friday evening lecture at the Royal Institution to the then recent work of L. P. Cailletet and R. P. Pictet, and exhibited for the first time in Great Britain the working of the Cailletet apparatus. Six years later, in the same place, he described the researches of Z. F. Wroblewski and K. S. Olszewski, and illustrated for the first time in public the liquefaction of oxygen and air, by means of apparatus specially designed for optical projection so that the actions taking place might be visible to the audience. Soon afterwards he constructed a machine from which the liquefied gas could be drawn off through a valve for use as a cooling agent, and he showed its employment for this purpose in connexion with some researches on meteorites; about the same time he also obtained oxygen in the solid state. By 1891 he had designed and erected at the Royal Institution an apparatus which yielded liquid oxygen by the pint, and towards the end of that year he showed that both liquid oxygen and liquid ozone are strongly attracted by a magnet. About 1892 the idea occurred to him of using vacuum-jacketed vessels for the storage of liquid gases, and so efficient did this device prove in preventing the influx of external heat that it is found possible not only to preserve the liquids for comparatively long periods, but also to keep them so free from ebullition that examination of their optical properties becomes possible. He next experimented with a high-pressure hydrogen jet by which low temperatures were realized through the Thomson-Joule effect, and the successful results thus obtained led him to build at the Royal Institution the large refrigerating machine by which in 1898 hydrogen was for the first time collected in the liquid state, its solidification following in 1899. Later he investigated the gas-absorbing powers of charcoal when cooled to low temperatures, and applied them to the production of high vacua and to gas analysis (see Liquid Gases). The Royal Society in 1894 bestowed the Rumford medal upon him for his work in the production of low temperatures, and in 1899 he became the first recipient of the Hodgkins gold medal of the Smithsonian Institution, Washington, for his contributions to our knowledge of the nature and properties of atmospheric air. In 1904 he was the first British subject to receive the Lavoisier medal of the French Academy of Sciences, and in 1906 he was the first to be awarded the Matteucci medal of the Italian Society of Sciences. He was knighted in 1904, and in 1908 he was awarded the Albert medal of the Society of Arts.
DEWAS, two native states of India, in the Malwa Political Charge of Central India, founded in the first half of the 18th century by two brothers, Punwar Mahrattas, who came into Malwa with the peshwa, Baji Rao, in 1728. Their descendants are known as the senior and junior branches of the family, and since 1841 each has ruled his own portion as a separate state, though the lands belonging to each are so intimately entangled, that even in Dewas, the capital town, the two sides of the main street are under different administrations and have different arrangements for water supply and lighting. The senior branch has an area of 446 sq. m. and a population of 62,312, while the area of the junior branch is 440 sq. m. and its population 54,904.
DEWBERRY, Rubus caesius, a trailing plant, allied to the bramble, of the natural order Rosaceae. It is common in woods, hedges and the borders of fields in England and other countries of Europe. The leaves have three leaflets, are hairy beneath, and of a dusky green; the flowers which appear in June and July are white, or pale rose-coloured. The fruit is large, and closely embraced by the calyx, and consists of a few drupules, which are black, with a glaucous bloom; it has an agreeable acid taste.
DEW-CLAW, the rudimentary toes, two in number, or the “false hoof” of the deer, sometimes also called the “nails.” In dogs the dew-claw is the rudimentary toe or hallux (corresponding to the big toe in man) hanging loosely attached to the skin, low down on the hinder part of the leg. The origin of the word is unknown, but it has been fancifully suggested that, while the other toes touch the ground in walking, the dew-claw merely brushes the dew from the grass.
D’EWES, SIR SIMONDS, Bart. (1602–1650), English antiquarian, eldest son of Paul D’Ewes of Milden, Suffolk, and of
