fluorescent lamp Type of electric discharge lamp consisting of a glass tube filled with a mixture of argon and mercury vapor. A current of elec¬ tricity causes the vapor to produce ultraviolet radiation that, in turn, excites a phosphor coating on the inside of the tube, causing it to fluo¬ resce, or reradiate the energy as visible light. Fluorescent lamps are cooler
and more efficient than incandescent lamps. They are commonly installed with diffusers as part of a suspended ceiling system. See also fluorescence.
fluoridation of water Addition of fluoride compounds to water (see fluorine) at one part per million to reduce dental caries (cavities). This practice is based on the lower rates of caries seen in areas with moderate natural fluoridation of water and on studies showing that sound teeth con¬ tain more fluoride than cavity-prone teeth and that fluorides help prevent or reduce dental caries. Fluoridation decreases the number of decayed, missing, and filled teeth in children (which increases if fluoridation is stopped), but it has provoked controversy in some cases. Excess fluoride may cause tooth mottling (a problem of appearance only) and, in higher doses, bone abnormalities. Fluoridation also helps prevent rickets in infants and children and helps the thyroid maintain a normal basal meta¬ bolic rate.
fluorine Vflur-.en, 'fl6r-,en\ Nonmetallic chemical element, chemical symbol F, atomic number 9. The lightest halogen, it is the most reactive element, forming compounds with all others except helium, neon, and argon (the lighter noble GASes). Its only valence is 1, in F 2 (the diatomic molecule) and fluorides. A toxic, pale yellow gas with a pungent odour, it can be produced only by electrolysis under special conditions. Its chief source is fluorite; it also occurs in cryolite, fluorapatite, seawater, bones, and teeth. Hydrogen fluoride (HF) is a raw material for many other fluo¬ rides. Its water solution, hydrofluoric acid, is used to clean metals and to polish, etch, or frost glass. Other fluorides are useful catalysts and raw materials. Sodium fluoride (NaF) is added to water and tin fluoride (SnF 2 ) to dental-care products to reduce dental caries (see fluoridation of water). Fluorocarbons are hydrocarbons in which some hydrogen atoms have been replaced by fluorine atoms; examples include Freons and Teflon.
fluorite or fluorspar Common halide mineral, calcium fluoride (CaF 2 ); the principal fluorine mineral. Fluorite occurs most commonly as a vein mineral and is often associated with lead and silver ores; it also occurs in cavities, sedimentary rocks, pegmatites, and hot-springs areas. It is wide¬ spread in China, South Africa, Mongolia, France, Mexico, Russia, and the central U.S. Fluorite is used in the manufacture of steel, aluminum fluoride, artificial cryolite, and aluminum. It is used in glassmaking, in iron and steel enamelware, in the production of hydrofluoric acid, in the refining of lead and antimony, and (as a catalyst) in the manufacture of high-octane fuels.
Flushing Northern section, Queens, New York, New York, U.S. Located at the head of Flushing Bay in the East River, it was settled in 1645 by English nonconformists and became a centre for Quakers (see Society of Friends). In the late 18th and early 19th centuries, it flourished as a township and then a village until it was absorbed by Queens in 1898. Flushing Meadow-Corona Park was the site of the 1939-40 and 1964-65 New York world’s fairs (the Hall of Science remains as an exhibition centre), and in 1946-49 it was the temporary headquarters for the UN. Flushing is the scene of the U.S. Open tennis championships and home to Shea Stadium.
flute Woodwind instrument in which the sound is produced by blowing against a sharp edge. In its broad sense, a flute may be end-blown, like the recorder, or may have a globular shape, like the ocarina. In its nar¬ row sense, discussed below, flute refers to the transverse flute of Western music. The transverse flute, a tubular instrument held sideways to the right, appeared in Greece and Etruria by the 2nd century bc. By the 16th century a family of boxwood flutes, with fingerholes but no keys, was in use in Europe. Keys began to be added in the late 17th century. Theobald Boehm’s 19th-century innovations resulted in the modern flute, which per¬ mits thorough expressive control and great agility. The cylindrical tube may be made of wood or, more often, a precious metal or alloy. Its range is from about middle C to the C three octaves higher. The flute family includes the piccolo (pitched an octave higher), the alto flute, and the rare bass flute. See also shakuhachi.
flux In metallurgy, any substance introduced in the smelting of ores to promote fluidity and to remove objectionable impurities in the form of slag. Limestone is commonly used for this purpose in smelting iron ores. Other materials used as fluxes are silica, dolomite, lime, borax, and fluo¬ rite. In soldering, the flux removes oxide films, promotes wetting, and prevents reoxidation of the surfaces during heating. Rosin is widely used as a noncorrosive flux when electronic equipment is soldered; in other applications, a water solution of zinc chloride and ammonium chloride may be used.
Liver fluke (Fasciola hepatica)
GRANT HEILMAN
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686 I Fluxus ► Foch
Fluxus \'fbk-s3s\ International avant-garde group of artists founded in Germany by U.S. artist George Maciunas (1931-78) in 1962. Its mem¬ bers, including Joseph Beuys, John Cage, and Yves Klein, explored media ranging from performance art to poetry to experimental music. Opposed to tradition and professionalism in the arts, the Fluxus group shifted the emphasis from what an artist makes to the artist’s personality, actions, and opinions. Throughout the 1960s and ’70s they staged “action” events, engaged in politics and public speaking, and produced sculptural works featuring unconventional materials. Though it was an influential move¬ ment in Europe, the group’s work frequently conflicted with authority and aroused much controversy.
fly In general, almost any small flying insect. In entomology, the term refers specifically to the approximately 85,000 species of two-winged, or “true,” flies (dipterans). Other insects called flies have wing structures that differ from that of dipterans.
Fly River River, New Guinea Island. One of the island’s largest rivers, it flows almost wholly through Papua New Guinea. For a short stretch of its middle course, it forms the border between Papua New Guinea and Indonesia. Rising in the Victor Emanuel Range in the central highlands, it flows south for about 700 mi (1,100 km) to the Coral Sea; much of it is navigable.
flycatcher Any of numerous small passerine birds that capture insects on the wing, particularly more than 100 Old World species of the family Muscicapidae and more than 400 New World species called tyrant fly¬ catchers (family Tyrannidae). The most common Old World species, the spotted flycatcher (Muscicapa striata), is 5.5 in. (14 cm) long and streaked grayish brown. It inhabits open woodlands and gardens eastward from Europe, where it breeds, through Asia. Tyrant flycatchers include the manakins, pewees, kingbirds, becards, and cotingas, among others. Most have a large head, short legs, and a broad bill (e.g., phoebes).
flying buttress Masonry structure typically consisting of an inclined bar carried on a half arch that extends (“flies”) from the upper part of a wall to a pier some distance away and carries the thrust of a roof or vault. A pinnacle (vertical ornament of pyramidal or conical shape) often crowns the pier, adding weight and enhancing stability. The flying buttress evolved in the Gothic era from earlier simpler, hidden supports. The design increased the supporting power of the buttress and allowed for the creation of the high-ceilinged churches typical of Gothic architecture.