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* BOOLE. 304 BOONE. so that the results of logical reasoning may be arrived at by an almost purely mechanical proc- ess. Much 'more valuable, liowever, are Boole's contributions to mathematics. The modern the- orv of invariants mav be said to date from a "memoir publislied by him in the Cambridge Mathematical Journal in 1841, and he was among the first to contribute to the general theory of covariants. His two larger matlie- matical works, the Treatise on Differential Equations (1859) and the Treatise on the Cal- culus of Finite Differences (1860), are stand- ards on their respective subjects. His special contributions were published in several scientific periodicals. A list of these papers may be found in the Royal Society's Catalogue of Scientific Memoirs. BOOM, bom. A iovra of the Province of Ant- werp, Belgium, about 10 miles south of the city of Antwerp (Map: Belgium, C 3). Its situation at the junction of the Brussels Canal with the river Rup'el makes it a place of considerable commer- cial importance. It has numerous and extensive brick and tile works, breweries, tanneries, ship- building yards, rope-works, sail-cloth manufac- tures, salt-works, etc. Population, in 1890, 14,100; in 1900, 15,700. BOOM (Dutch hoom, Ger. Baum, tree, beam). A long pole or spar used to extend the foot of certain sails of a ship; as the main-hoom, jib- boom. studdingsail-hoom. Some of the booms are stationary; others are pivoted at one end, the other being controlled by guys or sheets, and others like the studdingsail-booms which are only occasionally used, rig in and out by means of tackles. The space in the waist of a vessel of old type and used for stowing boats and spare spars is called the booms. To boom off a vessel or boat is to shove it away with spars. The term boom is applied also to a chain of floating logs fastened together at the ends and stretched across a river, etc., to stop floating timber. Hence, the name is adopted in military usage to denote a strong barrier, as of beams, or an iron chain or cable fastened to spars, extended across a river or the mouth of a harbor to prevent an enemy's ships from pass- ing. Such a boom should be protected by a battery or batteries, and the approaches thickly planted with submarine mines. It is considered best to have booms made double, one to stopthe way of ships that have penetrated the first. A chain for this jiurpose was stretched across the Hudson River at West Point during the American Revolution. The Russians efi'ectually closed the harbor of Sebastojiol with a lioom defense in 1854, thereby preventing the entrance of the English and French ships. This was done partly by sinking some of tlieir own ships, and partly by the laying of booms. Some of the most gallant and daring pieces of work that have been done by seamen have been in connec- tion with blowing up or cutting away booms in order to make a free passage for the vessels of the fleet. During the American Civil War, when Farragiifs fleet attacked New Orleans, formidal)le cliains stretched across the river, and, buoyed up by hulks, were first encountered and destroyed. The torpedo-netting of steel wire or rings used to protect a ship from toriiedoes which "may be discharged toward it, is held suspended 20 or more feet from the ship by means of a series of hinged booms. BOOMERANG (native name in New South Wales; bumarin, womunung, among the designa- tions for a club). A cuned missile of the Aus- tralians made of the green wood of the acacia or some other hard tree treated with fire. The B005IERA.N09 AND BOOMERANG-SHAPED CLUBS (In the British and Berlin Museums). boomerang averages 21/2 feet in length and 2Vi inches in width, is convex on one side and flat on the other, with a sharp edge along the curve convex, ^^'ben thrown with a certain movement of the hand (the grasping end is marked by in- cised lines, etc.), flat side down, convex side forward, this weapon will, after traveling some distance, retuiTi in a sort of ellipse almost to the feet of the thrower, who is also able to varj- its course consideraldy. In Australia the sliape, use, and power of the boomerang vary greatly — it ranges all the way from a mere toy to a large and powerful war weapon. It is some- times ornamented in simple fashion. Boomerang- like objects are claimed by some to have existed in ancient Assyria, Egypt, and elsewhere far outside of the 'Australian area, and Schoeten- sack (1901) has even claimed certain bone ob- jects belonging to prehistoric man in western Europe as boomerangs; but all this remains to be proved. Of late" years the boomerang has been the subject of mathematical and physical experimentation, and an excellent paper by Jlr. G. T. Walker, "On Boomerangs," is to be found in the Philosophical Transactions of the Royal Societg (London. 1897). BOOMSLANGE, bom'slang-e (Dutch 6001/1, tree + slang, Ger. Hchlange, snake). A beauti- ful South African tree-snake {Bucephalus ca- pensis), so variable that it has furnished several supposed species to zoology, and regarded as poisonous, though possessing no venom-glands. BOONE. A city and the county-seat of Boone County, Iowa, 4;i miles north by west of Des Moines; on the Chicago and Nortlnvestern and Chicago, Milwaukee and Saint I'aul railroads (Map: Iowa, D 2). It is in a region which abounds in coal, clay, and timber; and has an extensive trade in coal, grain, agricultural pro- duce, live stock, and lumber. The industrial establishments include flour-mills, brick and tile works, potteries, etc. There are also ex- tensive shops of the Chicago and Northwestern