one of the first to hold the hydrogen theory of acids. In 1815, in conjunction with Alexis Thérèse Petit (1791–1820), the professor of physics at the École Polytechnique, he made careful comparisons between the mercury and the air thermometer. The first published research (1816) dealt with the dilatation of solids, liquids and gases and with the exact measurement of temperature, and it was followed by another in 1818 on the measurement of temperature and the communication of heat, which was crowned by the French Academy. In a third, “On some important points in the theory of heat” (1819), they stated that the specific heats of thirteen solid elements which they had investigated were nearly proportional to their atomic weights—a fact otherwise expressed in the “law of Dulong and Petit” that the atoms of simple substances have equal capacities for heat. Subsequent papers by Dulong were concerned with “New determinations of the proportions of water and the density of certain elastic fluids” (1820, with Berzelius); the property possessed by certain metals of facilitating the combination of gases (1823 with Thénard); the refracting powers of gases (1826); and the specific heats of gases (1829). In 1830 he published a research, undertaken with Arago for the academy of sciences, on the elastic force of steam at high temperatures. For the purposes of this determination he set up a continuous column of mercury, constructed with 13 sections of glass tube each 2 metres long and 5 mm. in diameter, in the tower of the old church of St Geneviève in the Collège Henri IV. The apparatus was first used to investigate the variation in the volume of air with pressure, and the conclusion was that up to twenty-seven atmospheres, the highest pressure attained in the experiments, Boyle’s law holds good. In regard to steam, the old tower was so shaky that it was considered unwise to risk the effects of an explosion, and therefore the mercury column was removed bodily to a court in the observatory. The original intention was to push the experiments to a pressure equivalent to thirty atmospheres, but owing to the signs of failure exhibited by the boiler the limit actually reached was twenty-four atmospheres, at which pressure the thermometers indicated a temperature of about 224°C. In his last paper, published posthumously in 1838, Dulong gave an account of experiments made to determine the heat disengaged in the combination of various simple and compound bodies, together with a description of the calorimeter he employed.
DULSE (Ir. and Gael. duileasg), in botany, Rhodymenia palmata, one of the red seaweeds, consisting of flat solitary or tufted purplish-red fronds, fan-shaped in general outline and divided into numerous segments, which are often again and again divided in a forked manner. It varies very much in size and degree of branching, ranging from 5 or 6 to 12 or more inches long. It grows on rocks, shell-fish or larger seaweeds, and is used by the poor in Scotland and Ireland as a relish with their food. It is commonly dried and eaten raw, the flavour being brought out by long chewing. In the Mediterranean it is used cooked in ragouts and made dishes.
See W. H. Harvey, Phycologica Britannica, vol. ii. plates 217, 218.
DULUTH, a city and the county-seat of St Louis county, Minnesota, U.S.A., at the W. end of Lake Superior, at the mouth of the St Louis river, about 150 m. N.E. of Minneapolis and St Paul. Pop. (1880) 3483; (1890) 33,115; (1900) 52,969, of whom 20,983 were foreign-born and 357 were negroes; (1910 census) 78,466. Of the 20,983 foreign-born in 1900, 5099 were English-Canadians, 5047 Swedes, 2655 Norwegians, 1685 Germans, and 1285 French-Canadians. Duluth is served by the Duluth and Iron Range, the Duluth, Missabe & Northern, the Duluth, South Shore & Atlantic, the Chicago & North-Western (the North-Western line), the Great Northern, and the Northern Pacific railways. Situated attractively on the side and along the base of a high bluff rising 600 ft. above the lake level, Duluth lies at the W. end of Superior Bay (here called Duluth Harbour), directly opposite the city of Superior, Wisconsin. A narrow strip of land known as Minnesota Point, 7 m. in length and extending toward Wisconsin Point, which projects from the Wisconsin shore, separates the bay from the lake and forms with St Louis Bay one of the finest natural harbours in the world. The natural entrance to the harbour is the narrow channel between the two points, but there is also a ship-canal across Minnesota Point, spanned by a curious aerial bridge 400 ft. long and 186 ft. above the water.
The unusually favourable position for lake transportation, and the extensive tributary region in the N.W., with ample rail connexions, make Duluth-Superior one of the greatest commercial ports in the country. The two cities constitute the largest coal-distributing centre in the N.W., and have some of the largest coal-docks in the world. Upwards of twenty grain elevators, with a net capacity of nearly 35,000,000 bushels, which receive enormous quantities of grain from the Red River Valley, Manitoba, and the Dakotas, either for home manufacture or for transhipment to the East, are among the noteworthy sights of the place; and extensive ore-docks are required for handling the enormous and steadily increasing shipments of iron ore from the rich Vermilion and Mesabi iron ranges first opened about 1890. In 1907 more than 29,000,000 tons of iron ore were shipped from this port. Duluth is also an important hay market. There are flour and lumber mills, foundries and machine shops, wooden ware, cooperage, sash, door and blind, lath and shingle factories, and shipyards. In 1909 great mills of the Minnesota Steel Co. were begun here. In 1905 the factory product of Duluth was valued at $10,139,009, an increase of 29·8% over that of 1900. The St Louis river furnishes one of the finest water-powers in the United States.
The commanding heights upon which the principal residential section of the city is built render it at once attractive in appearance and healthful; there is a fine system of parks and boulevards, the chief of the former being Lester, Fairmount, Portland, Cascade, Lincoln and Chester. The popular Boulevard drive at the back of Duluth commands excellent views of city and lake. Among the principal buildings are the court house, the Masonic temple, chamber of commerce, board of trade, Lyceum theatre, Federal, Providence, Lonsdale, Torrey, Alworth, Sellwood and Wolvin buildings, St. Mary’s hospital, St. Luke’s hospital and Spalding Hotel. There is a public (Carnegie) library with 50,000 volumes in 1908. The building of the central high school (classical), one of the finest in the United States, erected at a cost of about $500,000, has a square clock tower 230 ft. high, and an auditorium seating 2000. The city also has a technical high school, and in addition to the regular high school courses there are departments of business, manual training and domestic science. At Duluth also is a state normal school, erected in 1902. The federal government maintains here a life-saving station on Minnesota Point, and an extensive fish hatchery.
The first Europeans to visit the site of Duluth were probably French coureurs-des-bois, possibly the adventurous Radisson and Groseilliers. The first visitor certainly known to have been here was Daniel Greysolon, Sieur Du Lhut (d. 1709), a French trader and explorer, who about 1678 skirted Lake Superior and built a stockaded trading-post at the mouth of Pigeon river on the N. shore. From him the place received its name. A trading-post was established near the present city, at Fond du Lac, about 1752, and this eventually became a depôt of Astor’s American Fur Company. There was no permanent settlement at Duluth proper, however, until 1853, and in 1860 there were only 80 inhabitants. Incorporated in 1870, in which year railway connexion with the South was established, its growth was slow for some years, the increase for the decade 1870–1880 being very slight (from 3131 to 3483); but the extension of railways into the north-western wheat region, the opening up of Lake Superior to commerce, and finally the development of the Vermilion and Mesabi iron ranges, brought on a period of almost unparalleled growth, marked by the remarkable increase in population of more than 850% between 1880 and 1890; between 1890 and 1900 the increase was 60%.
See J. R. Carey, History of Duluth and Northern Minnesota (Duluth, 1898); Leggett and Chipman, Duluth and its Environs (Duluth, 1895); and J. D. Ensign, History of St Louis County (Duluth, 1900).
DULWICH, a district in the metropolitan borough of Camberwell, London, England. The manor, which had belonged to the
