The late Dr. John Aitken, F.R.S., of Falkirk, Stirlingshire, contrived a means of gauging the dust contents of the atmosphere. This consists of a glass box about a centimetre in thickness. Two pieces of wet filter paper inside serve to keep the contained air damp. The bottom of the box is a micrometer plate, divided rectangularly in millimetres. It can be examined from above by a lens. An air-pump can withdraw definite volumes of air as desired. When the air is partially withdrawn, the expansion of the remainder produces cooling. The dust particles form nuclei for condensation of the vapour. They are thus precipitated on the plate, and counted, leaving the air dust-free. A measured quantity of the air to be tested is next drawn in and shaken up. Further operation of the air-pump causes its expansion, and the deposition of its dust particles, which can then be counted. Dr. Aitken found the proportion of dust on Ben Nevis to vary at different times from under 100 particles to over 14,000 per cubic centimetre. Over oceans the numbers were from about 500 on the Indian to 2000 on the Atlantic. But over cities 100,000 per cubic centimetre are frequently present. A puff of cigarette smoke was estimated to contain 4,000,000,000 particles.
Many phenomena are connected with the existence of dust in the atmosphere. As a result of Dr. Aitken's discoveries the belief largely prevailed that the formation of fog, of rain, and other varieties of precipitation, was necessarily dependent on dust particles as nuclei of condensation. Though they certainly function to a preponderating extent, it has been shown that gaseous particles can act similarly, particularly when air is ionized. Dust is the main cause of the scattering of the sun's rays which produces twilight, the blue of the sky, the gorgeous red and golden hues of sunrise and sunset, and the purple lights of advancing dusk. After the great Krakatoan eruptions of 1883, dust was carried in the upper atmosphere several times round the earth, and caused extraordinary colour effects. To a lesser degree similar phenomena followed the West Indian eruptions of 1902. The unusual sunlessness of the summer of 1912 was attributed to dust expelled in the preceding great eruptions at Katmai, Alaska.
Dutch Clover, Trifolium repens, commonly called white clover, a valuable pasture plant. It has a creeping stem; the leaflets are broad, obovate, with a horse-shoe mark in the centre; the white or pinkish flowers are in a globular head.
Dutch East Indies, forming a large and important colonial possession of the Netherlands Government, lie between 6° N. and 11° S., and 95° E. and 141° E. The colony includes Java and Madura, with the 'Outposts', which comprise Sumatra, the south-east and west portions of Borneo, Banca, Billiton, Celebes, the Timor and Riau-Lingga Archipelagos, the smaller Sunda Islands, and the north and west of New Guinea. The total area is about 735,000 sq. miles; the population of about 47,000,000 is composed of 46,000,000 natives of Malay race, 832,000 Arabs, Chinese, and other Orientals, and some 80,000 whites. The origin of the colony may be traced to the treaty made by the Dutch with the Sultan of Bantam in Sumatra (1595), which was followed by the formation of the Dutch East India Company (1602), the establishment of Batavia (1619) on the ruins of the native town of Jacatra, and the settlement in Sumatra (1677). The Dutch East India Company was dissolved in 1798, since which date the colony has been administered from the Netherlands by a Governor-General, who, assisted by a Council of five members nominated by the queen, has the power to pass laws, subject to the general regulations adopted in 1854. Some of the outlying islands are, however, administered by their native princes under the 'advice' of a Netherlands Resident. Batavia (population about 234,000), a town in the province of the same name on the north-west coast of Java, is the administrative capital and an important centre of trade. Java and Sumatra, containing about three-fourths of the total population of the colony, are self-supporting as regards food, besides producing for European consumption large quantities of tobacco, tea, coffee, sugar, cinchona, tin, rubber, and copra. The colonial army numbers some 1200 officers and 40,000 men; compulsory service for white men within certain age-limits was adopted in 1918. There is also a small naval force.—Bibliography: Bemmelen and Hooyer, Guide to the Dutch East Indies; W. Cool, With the Dutch in the East; J. M. Brown, The Dutch East.
Dutch Metal, an alloy containing 84.5-84.7 per cent of copper and 15.5-15.3 per cent of zinc, with a fine golden-yellow colour, ductile, malleable, and tenacious. When beaten out by a process analogous to that for gold-leaf, until the sheets are less than 1/50,000th part of an inch thick, it constitutes Dutch leaf or Dutch foil, and is used as a cheap substitute for gold-leaf for ornamental purposes.
Dutch Pink, a bright yellow colour used in distemper, for staining paper-hangings, and for other ordinary purposes. It is composed of chalk or whiting coloured with a decoction of birch leaves, French berries, and alum.
Dutch Rush, Equisētum hyemāle, one of the plants known as horse-tails, with a firm texture and so large an amount of silica in the cuticle that it is employed as a fine sand-paper for polishing delicate woodwork. The plant is found in marshes and woods in Britain, but for economic use it is imported from Holland, whence its popular name.
Dutrochet (du˙-tro-shā), René Joachim Henri, a French physiologist, born in Poitou in 1776, died at Paris in 1847. He served for some time as medical attendant to Joseph Bonaparte during the Spanish campaign 1808-9; but afterwards returned to France, and retired to the estate of Châteaurenault, where he devoted himself exclusively to physical and physiological studies. His chief works have been published in a collective form with the title Mémoires pour servir à l'Histoire Anatomique et Physiologique des Végétaux et des Animaux (1837, 2 vols.).
Dvina, Northern, a Russian river formed by the union of two small streams in the government of Vologda. It flows in a north-westerly direction, and falls by four mouths into the White Sea. At Archangel, before it divides, it is 4 miles broad. It is navigable as far as Suchona, and is connected with the Volga and Neva by canal.