8IL 



8IL 



taining the twelfth part of the zodiac, or 

 30. The signs are reckoned from the 

 point of intersection of the ecliptic and 

 equator, at the vernal equinox, and are 

 named respectively, Aries, Taurus, Ge- 

 mini, Cancer, Leo, Virgo, Libra, Scorpio, 

 Sagittarius, Capricornus, Aquarius, Pis- 

 ces. 2. In algebra, a character indi- 

 cating the relation of the quantities of an 

 expression, and the operations to be per- 

 formed upon them ; as 4- (plus), denoting 

 addition , and (minus) , denoting subtrac- 

 tion. See POSITIVE and NEGATIVE- also 

 QUANTITY. There are also signs of Mul- 

 tiplication and Division, of Equality, of 

 Greater and Less (or Inequality), q.v. 



SIG'NALS, NAVAL. A system of symbols 

 addressed to the eye, as flags, lights, &c., 

 for communicating intelligence at dis- 

 tances too great for the human voice. 



SIG'NATURE, from signo. 1. In. printing, a 

 letter put at the bottom of the first page 

 of each sheet, as a direction to the binder 



in folding, gathering, and collating. 2. 



In music, the flats or sharps placed after 

 the clef, at the beginning of the staff. 



SIG'NET. A seal. The Clerk of the Sig- 

 net is an officer in attendance upon the 

 principal Secretary of State, and who has 

 the royal signet in his keeping, for the 

 signing of letters, grants, &c. 



SIGN-MAN'UAL, in law, is used to signify 

 a writing signed by the sovereign's own 

 hand. 



SILE'NE. The Catchfly. A very exten- 

 sive genus of caryophyllous plants. De- 

 candria Trigynia. There are twelve 

 British types, among which are the Blad- 

 der and the Moss Campions, English, 

 Dover, Nottingham, Spanish, Lobel's, and 

 Nautical Catchfly. There are upwards of 

 100 species in all. 



SI'LEX. The Latin word for flint. An 

 oxide of silicium or silicon, constituting 

 the greater part of all the rocks of which 

 the crust of the earth is composed. See 

 SILICA. 



SIL'HOCETTE. In the fine arts, the re- 

 presentation of an object in a black co- 

 lour, lightened to represent the prominent 

 features, and touched with gum to indi- 

 cate the shadows. 



SIL'ICA, from silez. One of the primitive 

 earths (strictly an acid), constituting the 

 principal portion of the scintillating 

 stones and minerals, which compose the 

 crust of the globe, and occurring nearly 

 pure in flint, rock-crystal, quartz, agate, 

 calcedony, jasper, &c. The only acid that 

 dissolves silica is the hydrofluoric, but it 

 is soluble in alkaline solutions, and com- 

 bines with many of the metallic oxides : 

 hence it is regarded by chemists as an 

 acid, and called the silicic acid. It is ob- 

 tained perfectly pure, and in the finest 

 state of comminution, by passing silicated 

 fluoric acid gas through water ; the silica 



is precipitated, and may be separated by 

 filtration. The silica thusobtained, being 

 well washed and ignited, is a white and 

 exceedingly light powder. It consists of 

 48'04 silicon, and 51'96 oxygen. It melts, 

 before the flame of the oxy-hydrogen 

 blowpipe, into a colourless glass. 



SIL'ICATE. A compound of the silicic 

 acid (silica) and a base, such as alumina, 

 lime, magnesia, potash, soda, &c. The 

 silicates are abundant in nature. Thus 

 felspar and leucite are silicates of alumina 

 and potash ; albite and analcime are sili- 

 cates of alumina and soda ; stilbite, preh- 

 nite, mesolite, labradorite, mica, &c., are 

 silicates of ammonia and lime ; steatite 

 and serpentine are silicates of magnesia ; 

 augite and hornblende are silicates of lim> 

 and magnesia (Tire). The various kinds 

 and qualities of glass are all silicates. 



SILI'CEOUS. Flinty, containing silex. 



SILICICAL'CE. The name given by 

 Brongniart to a mineral substance which 

 occurs in amorphous masses in thin beds, 

 under strata of compact limestone, in 

 Provence ; it is a mixture of flint (silica) 

 and carbonate of lime. 



SILICIFICA'TION. Conversion of a sub- 

 stance into stone, by the infiltration of 

 siliceous matter ; petrifaction. 



SILI'CIUM, ) The basis of silica. By 



SIL'ICON. } passing the vapour of po- 

 tassium over silica in an ignited tube, 

 Sir H. Davy obtained a dark-coloured 

 powder, which he supposed to contain 

 silicium, or the basis of the earth. This 

 has since been obtained in a pure state by 

 Berzelius, who places it among the sim- 

 ple non-metallic combustibles. It appears 

 to have a great analogy to boron. For 

 this reason it has been named silicon. 



SILIC'OLA, ) Lat. dim. of siliqua. In 



SIL'ICCLE. / botany, a pouch or pod, 

 scarcely longer than it is broad. 



SILICULO'SA. The name of the first order 

 of plants in the class Tetradyjiamia of the 

 Liunaean system, containing such as have 

 a broad and short pod, or whose fruit are 

 siliculae. Epithet siliculose. 



SIL'IQUA, Lat., from silo, a snub nose. 

 Apod: a long, dry, membranaceous peri- 

 carp, or seed-vessel of two valves, sepa- 

 rated by a linear receptacle, along the 

 edges of which the seeds are arranged 

 alternately. 



StLiauo'sA. The name of the second 

 order of plants in the class Tetradynamia 

 of the Linna?an system, containing such 

 as have long pods (siliqua). 



SiLiaro's.. The name of a natural order 

 of plants in the natural method of Linne, 

 consisting of such as have a siliqua or 

 silicula, with a tetradynamic and cruciate 

 flower. 



SILK. A fine glossy thread or filament, 

 spun by various species of caterpillars of 

 the genus Phaleius, Lin., especially tht 



