DUST. 549 DtrSTYFOOT. of clouds, (lustless air is necessary for the forma- tion of rain. W'lien liust is very tine and uniform in size, it gives rise to iK'UUtiful optical phenomena due to the dilVraction and interference of light, such as the wonderful red. green, and yellow sunsets and sunrises, and the blue siuis visible during the daytime in the years 1S83-85. These weurred in connection with the vapor-dust from the Kraka- toa eruption: but similar phenomena have been observeil on numerous other occasions after vol- canic eruptions. Among the important works on this subject may be mentioned C. G. Elirenberg, on Infusoria (Leipzig, 1S3S) and Microgeoloyii (Berlin, 1856) : .J. W. Bailey, numerous papers in the Amcruan Jounuil of >^cie»cc, from 1838 to 185G; John Aitken, numerous papers in The Trans- uctions of the Royal Society of Edinburgh, and his last paper, Observations of Atmospheric Dust, read before the Chicago Meteorological Con- gress of 1893 (see United States Weather Bureau Bulletin Xo. 11, pp. 734-54) : Carl Harus, on Cloudy Condensation (see bulletins and reports of the United States Weather Bureau) : G. J. Svnions, The Eruption of Krakatoa (London, 1888). Cosine OR JIeteoric Du.st. The fact that meteors entering the earth's atmosphere from interplanetary space are burned up and disappear leads to the rational conclusion that the result- ing debris must remain in the atmosphere in the shape of very fine dust, or larger particles gradu- ally descending to the earth's surface. In many cases the cloud left behind a meteor has remained visible for a relatively long period — in some cases three or four hours— during which it changes shape and diffuses, probably being il- lumined by the sunlight of a distant twilight like the so-called phosidiorcscent clouds. In a few cases the dust collected by Xordcnskjold from the surface of snow has been found to contain metallic iron and nickel. In still fewer cases hailstones have had a metallic nucleus. Arago first suggested that these metallic dusts are the remnants of the shooting stars or meteors: they have therefore been spoken of as cosmic or meteoric dust, but in all case.s except those of me- tallic iron or nickel the ordinary mineral dusts undoubtedly come from the earth itself. Many volcanic eniptions send inmiense volumes of dust into the air: in 1883 Krakatoa sent up four cubic miles of solid rock ground into impalpable dust, the finest particles of which floated about for several years. Besides the larger shooting stars and aerolites, there may well exist even the dust in the interplanetary space, some of which must frequently enter the earth's atmos- phere; but except in the case of the nickel-iron compounds it seems at present impossible to dis- tinguish such cosmic dust from that which orig- inates on the earth itself. DiST-WiiiHi.s .XD DfST-SrORMS. The eddies of wind, especially those on a hot summer after- noon, that form small whirls of ascending hot air. carrj' up leaves and dust to a considerable height. Tndor most favorable cireimi stances these may be elevated to the level of the clouds, but under ordinarv" circumstances they are cliar- acteristic of the driest weather, and scarcely rise 1000 feet before they subside. On the hot plains of India and the western arid regions of the United States, which are subject to verj' high temperatures in the sunsliine, the du»t-column becomes a very tall colunui, with a rapid whirl- ing motion, having a thin, hazy axis, due to the condensation of aiivieous vapor in the region of low pressure that must mark the central axis. The dust-stx>rms of India have been i)ictured and described best by Badileley in his book un<ler that name, published in London in 1880. He figures not merely isolated dust - whirls, but groups of many such 'dancing around a central region, whence they are known as 'dancing devils.' or remarkable combinations of many whirls into figures illustrating most complex forms of vor- tex motion, some of which are stable and some unstable. These are all caused by the rapid ascent and whirl of air that is heated intensely by contact with the hot soil and hot dust. DcsT CofXTEK. .
instnnnent invent<>d by
Mr. .John .itken for counting the total number of particles of dust in a small volume of air. In this instrument a definite quantity of air is sud- denly and forcilily expanded, whereby ifis cooled below the dew-point, and immediately a fog or haze is formed within it whose density depends upon the quantity of moisture and the quantity of dust (hat is present. Within a short time these particles of fog descend to the bottom, falling upon a plate of black glass ruled otf into small squares. With the help of a hand lens it is easy to count the number of particles per square, whence we calculate the number per cubic centimeter of air. Instead of this dust-counter, one may use Aitken's koniscope. in which we estimate the apparent cloudiness due to the dust. These instruments are described in his report in Bulletin Xo. 11 of the United States Weather Bureau. The investigation of dust is an important branch of work in meteorology and in bacteriol- ogy', and the whole subject is known as koniology. DUS'TAN, H.NN'.Ti (1657—?). A heroine of the early Indian wars in New England. At the time of the attack on Haverhill, ilass.. March 15, 1697 (see Haverhill), the Indians captured Mrs. Dustan and her nurse, Mary Xeflf. and killed the youngest Dustan child, an infant only a week old. Mrs. Dustan's husband. Thomas Dustan, with their other seven children, however, managed to escape death. The captives were assigned to an Indian family consisting of two men. three women, and seven children, and were led off toward one of the larger Indian villages. On an island (now called Dustan's Island) six miles above the present Concord. N. H., Mrs. Dustan and hor nurse, assisted by a captive Eng- lish boy. Samuel Leonardson. killed and scalped all of their captors except one squinv and a small boy. .fter a- toilsome journey they reached tneir homes in safety. The story of their exploit spread rapidly, was told and retold at New Eng- land liresides for several generations, and has furnislied the theme for much romance and verse. The name is also spelled Dustin and Dnston. Consult Mirick. History of Haverhill (Haverhill, 13.32). DUST-BRAND. See Smut. DUSTYFOOT (OF. pirpoudreux. ML. prde- pulverosus. peddler). . court of summary juris- diction established at fairs and markers in Eng- land for the sjx-edy determination of questions arising between those who resorted to the same.
