(EST 



OLE 



ore, from Bourg d'Oisans, whence it is 

 also called Oisanite. 



OCTAHE'DRON (okto), eight, Upa, 

 a seat). In Geometry, a solid figure con- 

 tained by eight equal and equilateral 

 triangles. 



OCTANDRIA (oktw, eight, avr^p, a 

 male). The eighth class of plants in the 

 Linnaearj system, characterized by their 

 flowers having eight stamens. 



Octo-gynia [jvvt], a female). The name 

 given by Linnaeus to those orders of 

 plants which have eight pistils in their 

 flowers. 



O'CTANS HADLEIE'NSIS. Hadley's 

 Octant ; a modern southern constellation, 

 consisting of forty-three stars. 



OCTANT, A term applied to an in 

 termediate point between a quadrature 

 and a syzygy of the moon. See 

 Phases. 



O'CTAVE (octavus, the eighth). In 

 Music, the simplest and most consonant 

 interval, in which the higher note makes 

 twice as many vibrations as the funda- 

 mental note from which it is derived ; its 

 ratio is, therefore, that of 1 ; 2 I * 4 I 8, 

 &c. This relation serves as the principal 

 unit of measurement in music, its entire 

 range embracing at most nine entire 

 octaves, rising from the deepest note, 

 which makes 32 vibrations in a second, 

 to the highest, which performs 16,384 

 vibrations in the same time. 



0CT0'P0DA(6ktw, eight, ttoi;?, 7ro5op, 

 a foot). A designation of animals which 

 have eight feet. The name of those 

 Cephalopods which have eight prehensile 

 organs attached to the head. 



OCYPO'DIANS {wKvf, swift, iroh^, a 

 foot). A tribe of brachyurous crustace- 

 ans, placed by Milne Edwards between 

 the Pinnotherians and the Gonoplacians, 

 and named from the genus Ocypoda. The 

 family are characterized by their rapidity 

 in running. 



O'DERIT. An opaque black sub- 

 stance, occurring in Sweden : it is pro- 

 bably black mica ; for it is capable of being 

 split, like mica, into thin leaves. 



CENANTHIC ETHER {olvo^, wine, 

 avOos:, flower). An oily liquid, which 

 gives the characteristic odour to all 

 wines. 



(Enanthic acid. An acid found in the 

 foregoing compound, in combination with 

 ether. 



(E'STRIDiE {oestrus, a gad-fly). The 

 Bot-flies ; a family of Dipterous insects, 

 belonging to the section Athericera, re- 

 markable for the peculiar habitation of 

 210 



the larvae, and for the absence of any 

 proper mouth in the imago state. 



OFFICI'NA SCULPTORIA. A mo- 

 dern southern constellation, consisting of 

 twelve stars. 



OFFING. If we sail out of sight of 

 land, whether we stand on the deck of 

 the ship, or climb the mast, we see the 

 surface of the sea — not losing itself in 

 distance and mist, but terminated by a 

 sharp, clear, well-defined line, or offlfig, 

 as it is called, which runs all round us in 

 a circle, having our station for its centre. 



O'FFSET. Propagulum. A short 

 branch of certain herbaceous plants, 

 which is terminated by a tuft of leaves, 

 and is capable of taking root when sepa- 

 rated from the parent plant, as in house- 

 leek. It differs little from the runner. 



O'GAM or OGMA. An occult form 

 of writing among the Irish, apparently 

 of great antiquity. The term is a primi- 

 tive Celtic word, signifying the secrets of 

 letters. 



OGY'GIAN DELUGE, A great in- 

 undation mentioned in fabulous history, 

 as having taken place in the time of 

 Ogyges, king of Attica, whose death is 

 fixed in Blair's chronological tables in 

 the year b.c. 1764. 



OHM'S LAW. An important law 

 which refers to all the causes which tend 

 to impede the action of the voltaic bat- 

 tery. It is, that " the intensity of an elec- 

 tric current, when a battery is in action, 

 is directly as the whole electromotive 

 force in operation, and inversely as the 

 sum of all the impediments to conduc- 

 tion." It may, therefore, be expressed by 

 a fraction, whose numerator is the elec- 

 tromotive force, and its denominator the 

 sum of the resistance of all its parts, 



OrS ANITE. An ore of titanium, from 

 the department of Oise. 



OLD RED SANDSTONE. A forma- 

 tion lying immediately below the Car- 

 boniferous group. The term Devonian 

 has been recently proposed for strata of 

 this age, because in Devonshire they are 

 largely developed, and contain many 

 organic remains. 



OLEA'CE^. The Olive tribe of dico- 

 tyledonous plants. Trees or shrubs 

 with leaves opposite ; flowers regular, 

 monopetalous, hermaphrodite, or dioe- 

 cious ; stamens two ; ovarium simple, 

 superior, 2-celled ; seeds pendulous. 



OLEFIANT GAS {oleum, oil, fio, to 

 become). A compound gas consisting 

 of carbon vapour and hydrogen, and now 

 viewed as a compound of the organic 



