Sikorski, Wtadystaw (Eugeniusz) (b. May 20, 1881, Tuszow Narodowy, Pol., Austria-Hungary—d. July 4, 1943, Gibraltar) Polish gen¬ eral and politician. He served in the Austrian army and in World War I was head of the Polish Legion, which joined with Austria against Russia. He served as prime minister of Poland (1923—24) and as minister of mili¬ tary affairs (1924-25). From 1928 he joined the opposition to the gov¬ ernment controlled by J6zef Pilsudski. After the German invasion of Poland (1939), he became prime minister of the Polish government-in-exile. When he asked Joseph Stalin to allow the Red Cross to investigate the Katyn Massacre, Stalin broke off Soviet-Polish diplomatic contact. Sikor¬ ski died in an airplane crash several months later.
Sikorsky, Igor (Ivan) (b. May 25, 1889, Kiev, Russian Empire—d. Oct. 26, 1972, Easton, Conn., U.S.) Russian-U.S. pioneer in aircraft design. After studying engineering in Kiev, he set up his own shop to develop the helicopter. In 1910, after failing to build a workable model, he turned to fixed-wing airplane design, and in 1913 he built the first
four-engine airplane, with an inno¬ vative enclosed cabin. He immi¬ grated to the U.S. in 1919. In 1931 he produced the twin-engine amphibian aircraft that became the model for Pan American World Air¬ ways' “Clipper.” In 1939 Sikorsky finally realized a viable helicopter design. He directed his company, a division of United Aircraft Corpora¬ tion, from 1929 to 1957.
silage Ysl-lij\ or ensilage
Ven-s3-lij\ Forage plants such as com, legumes, and grasses that have been harvested at early maturity, finely chopped, packed tightly to exclude air, and stored in tower silos, pits, or trenches. Properly stored silage ferments slightly and keeps for several months. It is used as animal feed.
silane Vsi-.lan, 'sl-,lan\ or silicon hydride Any of a series of inor¬ ganic compounds of silicon and hydrogen with covalent bonds and the general chemical formula Si„H (2 „ + 2 y Silanes are structural analogs of saturated hydrocarbons (see saturation; alkane) but are much less stable. All burn or explode when exposed to air and react readily with halogens or hydrogen halides to form halogenated silanes and with olefins to form alkylsilanes, products used as water repellents and as starting materials for silicones.
silenus See satyr and silenus
Silesia \si-Te-zho\ Polish Slqsk \'shlask\ German Schlesien \'shla-ze-on\ Historic region, east-central Europe. It now lies mainly in southwestern Poland, with parts in Germany and the Czech Republic. It was originally a Polish province that became a possession of the Bohemian crown, and thus part of the Holy Roman Empire, in 1335. Because of suc¬ cession disputes and the region’s prosperity, there were at least 16 Silesian principalities by the end of the 15th century. It passed to the Austrian Habs- burgs in 1526; it was taken by Prussia in 1742. After World War I it was divided between Poland, Czechoslovakia, and Germany. During World War II Polish Silesia was occupied by Germany and was the site of atroci¬ ties against the population by Nazi and, later, Soviet forces. In 1945 the Allied powers assigned virtually all of Silesia to Poland; today its nine Pol¬ ish provinces contain almost one-fourth of Poland’s population.
Silhak See Practical Learning School
silhouette \,si-lu-'et\ Outline image or design in a single solid, flat colour, giving the appearance of a shadow cast by a solid figure. The term is usually applied to profile por¬ traits in black against white (or vice versa), either painted or cut from paper, especially popular c. 1750- 1850 as the least expensive method of portraiture. The name derives from Etienne de Silhouette, Louis XV’s finance minister, notorious for his frugality and his hobby of mak¬ ing cut-paper shadow portraits. In 17th-century Europe, shadow por¬ traits and scenes were produced by drawing the outline cast by candle¬ light or lamplight; when paper became widely available, they were often cut out freehand directly from life. Photography rendered silhou¬ ettes nearly obsolete, and they became a type of folk art practiced by itinerant artists and caricaturists.
silica mineral Vsi-li-koN Any of the forms of silicon dioxide (Si0 2 ),
Silhouette portrait by Charles Willson Peale; in the Library of Congress, Washington, D.C.
COURTESY OF THE LIBRARY OF CONGRESS, WASHINGTON, D.C.
© 2006 Encyclopaedia Britannica, Inc.
1752 I silicate mineral ► Silla
including quartz, tridymite, cristobalite, coesite, stishovite, melanophlog- ite, lechatelierite, and chalcedony. Various kinds of silica minerals have been produced synthetically.
silicate mineral Any of a large group of silicon-oxygen compounds that are widely distributed throughout much of the solar system. The sili¬ cates make up about 95% of the Earth’s crust and upper mantle, occur¬ ring as the major constituents of most igneous rocks and in appreciable quantities in sedimentary and metamorphic rocks. They also are important constituents of lunar samples, meteorites, and most asteroids. In addition, planetary probes have detected them on the surfaces of Mercury, Venus, and Mars. Of the approximately 600 known silicate minerals, only the FELDSPARS, AMPHIBOLES, PYROXENES, MICAS, OLIVINES, FELDSPATHOIDS, and ZEOLITES are significant in rock formation.
siliceous rock \s9-Ti-shos\ Any of a group of sedimentary rocks that consist largely or almost entirely of silicon dioxide (Si0 2 ), either as quartz or as chert, the most common siliceous rock. It occurs in beds and in nod¬ ules. Bedded cherts may be an original organic or inorganic precipitate. Nodular cherts appear to be produced by the alteration of preexisting sedimentary rock. In this process silica distributed throughout the rock dissolves and reprecipitates to form nodules.
silicon Nonmetallic to semimetallic chemical element, chemical symbol Si, atomic number 14. Second only to oxygen in abundance in Earth’s crust, it never occurs free but is found in almost all rocks and in sand, clay, and soils, combined with oxygen as silica (silicon dioxide, Si0 2 ) or with oxygen and metals as silicate minerals. It occurs in many plants and some animals. Pure silicon is a hard, dark gray solid with a metallic lus¬ tre and the same crystal structure as diamond. It is an extremely impor¬ tant semiconductor; doped (see dopant) with boron, phosphorus, or arsenic, it is used in various electronic circuit and switching devices, including computer chips, transistors, and diodes. Silicon is also used in metallurgy as a reducing (see reduction) agent and in steel, brass, and bronze. Its usual valence in compounds is 4. Silica is used in the form of sand and clay for many purposes; as quartz, it may be heated to form special GLASSes. Sili¬ cates are used in making glass, enamels, and ceramics; sodium silicates (water glass) are used in soaps, wood treatment, cements, and dyeing. See also silane; silicone.
silicon hydride See silane
Silicon Valley Industrial region, west-central California. Roughly bounded by San Francisco Bay on the north, the Santa Cruz Mountains on the west, and the Diablo Range on the east, it takes its (unofficial) name from the extensive use of silicon in the region’s electronics indus¬ tries. The U.S. government invested heavily in the region’s industry fol¬ lowing World War II. A second economic surge occurred with the proliferation of personal computers in the 1980s, and a third surge followed the growth of the Internet in the 1990s.