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* SIREN. 203 SISKIN. superposed; but are checked when the upper phite is turned a little, readmitted when the plate turns a little farther, and so on. The holes are pierced obliquely through the upper |)lale, so that the issuing stream makes it turn ahout its axis. The sounds given by this instrument are cxeeedinglj- pure (see Acoustics ), like those of the flute or tuning fork. The axis of the ujiper plate carries an endless screw. S, which turns a light train of wheels, G and H, with hands and dials resembling those of a gas meter, so that when, by proper adjustment of the pressure of the hollows, the instrument gives steadily some definite note, corresponding with that of an organ pipe or tuning fork whose pitch we desire to ascertain, we may observe the number of turns in any number of seconds by a stop-watch. The number of puH's is obviously to be found from this by multiplying the number of holes in the plate. A large instrument operated by steam is used as a fog signal, while more complex forms, such as Hclmholtz's double siren, have been devised for investigations in the more advanced fields of acoustics. Consult: T^Tidall. .S'oHiirf.- JluUer- Pouillet, Lehrbuch der Physik (Brunswick, 1S97): Helmholtz, Toneinpfiiidinu/rn. Englisli translation by Ellis (London and New York, 1895). See .IcorsTics ; Fog-Signals. SIBEN. An eel-like batrachian of the de- graded family Sirenidae. See Mud-Puppy. SIBENIA (Xeo-Lat, nom. pi., from Lat. siren, siren). An order of large aquatic herbivorous mammals, of doubtful affinity, including the sea- cows, manatees, and dugongs (qq.v.). The early fossil members of this group, found in the Eocene deposits, differ from the modern forms in show- ing a slightly less marked degeneration from the normal mammalian type. They have more primi- tive dentition and better developed bind limbs. Their origin is unknown, for they appeared sud- denly with their peculiar characters fully evolved in the Eocene. The principal fossil genera are Prorastomvis and Halitherium. SIRIASIS. See Heat-Stroke. SIR'IUS (Lat., from Gk. SnVfof, Seirios; probably connected with Skt. tvis. to excite, sparkle, flame, Lith. tviskcti, to lighten). A star of the first magnitude, the brightest in the heavens, and situated in the constellation Cants Major (q.v. ). or the 'gi-eat dog.' For this reason it is also called the dog-star. It has long been known to possess a 'proper motion' (i.e. an inde- pendent progressive motion), which was once be- lieved to be uniform, but has been shown to con- sist of an undulatory progressive motion. As soon as this became known, astronomers recog- nized that it could be due to one cause only: Sirius must have a companion star, and the revo- lution of both about their common centre of gravity would place Sirius alternately in advance of its average position and again behind it. Sa'f- ford (q.v.) was able to predict the position of such a companion, supposing it to be too minute to be seen; and it was actually discovered in the predicted place, in January, 18fi2, by Alvan Clark, of Cambridgeport, Mass., while observing Sirius through a new and powerful telescope which he had just made. The Egyptians called Sirius 'Sothis,' and at one time its heliacal rising (q.v.) was a sure fore- VOL. XVIII.— u. runner of the rising of the Nile; while among the Komans it was considered as a star of evil omen. The term dog-star' was also applied to Procyon, a bright double star in I'uiiis Minor, the small companion of which was found by Schaebcrle at the Lick Observatory in IS'.Mi. Sec Star for discussion of paralla.x and distance from the earth. SIR JOHN OLDCASTLE. A play by Dray- ton, Munday, Wilson, and Ihithaway, printed in lUOO with Shakespeare's name on the title-page, afterwards withdrawn. It is founded on the story of Lord Cobham, whose name was first used l)v Sliakcspcarc for Sir .fnlin FalstafT. SIR LATJNCELOT (lan'sc lot) GREAVES, The .dvextures of. A romance by Smollett (1701) in imitation of Don Qnixote. The scene is the England of George 11., and Sanclio Panza's place is supplied by an old sea captain. SIROCCO (It., from Ar. shani. east, from sharafjo. to rise [of the sun] ), A hot wind. In the desert of Sahara the sirocco is a hot, dry wind with clouds of dust, not so violent as a simoom (q.v.). Along the northern border of the Mediterranean two classes of warm winds are called the sirocco — the warm, moist, sultry wind folloAved by rain, and the liot dry wind from the soutli that frequently brings a dusty haze. SIR ROGER DE COV'ERLEY. See Coveb- ley. Sir RooER de. SIRVENTES, or Sirvente. A name applied to a class of poems important in Provencal lit- erature, usually, in contradistinction from the love-songs, dealing with contemporary social or political conditions, and frequently of a satiric nature. See Provencal Literature, SISAL, A fibre obtained from an American agave, which is cultivated in tropical America. See Hemp, Sisal. SISCO. A whitefish. See Cisco. SISCOWET. A salmon {Salmo siscawet) of the deeper waters of Lake Superior, where it is numerous. It differs so little from the land- locked salmon of other northern lakes, called namaycush in Canada, that some ichthyologists regard it as a mere variety of that widespread form. SISEN'NA, Lucius Cornelius (c.I 19-67 B.C.), A Eoman annalist, considered by Cicero superior as an historian to any of his predeces- sors, (Brut. 64, 288,) He was pra-tor in the year of Sulla's death (B.C. 7S), and during the war against the pirates (B.C. 07) was appointed by Pompey commander of the army at Crete. He is mentioned, also, as a friend and defender of Verres (Cicero, T'err., ii. 4;), 100). Sisenna's works included his Historia-, in more than 12 books, which embraced the history of his own time, and a Latin translation of the Mi- lesian tales (Mi?.r!(naKa) of Aristides. The commentaries on Plautus which were formerly ascribed to Sisenna were probably written by another person of the same name. The few ex- tant fragments of the JJistoriir are published in Peter's IJistoricorum Romannrum Fragmenta (Leipzig. 1883). Consult Schneider, De Sisennm Historia' Reliquiis (Jena, 1882). SISKIN (from Slovenian rhizhel-, Russ. chiz- In'i. siskin: connected with OPers. r:ilix. siskin). A small finch of the Old World (iSpinus spinus) ,