SPH 



SPI 



found in England, but appears to be ex- 

 tremely rare. 



SPHENE. Prismatic titanium ore; 

 a silico-titanite of lime, comprising the 

 common and the foliated varieties. 



SPHERE {<T<paipa, sphsera). A geo- 

 metrical solid described by the revolution 

 of a semicircle about its diameter, which 

 remains unmoved, and constitutes the 

 axis of the sphere. A sphere is bounded 

 by a curve surface, such that every point 

 thereon is situated at an equal distance 

 from a point within the solid called the 

 centre. The diameter of a sphere is any 

 straight line which passes through the 

 centre, and is terminated both ways by 

 the superficies of the sphere. 



1. The term Sphere is applied, in astro- 

 nomy, to the great concavity formed by 

 the space surrounding our globe, in 

 which we see the celestial bodies. It 

 appears to revolve upon the two poles. 



2. Those places with respect to which 

 the poles are situated in the horizon, are 

 said to have a right position of the sphere ; 

 those whose horizon coincides with the 

 equator, have a parallel position of the 

 sphere. For all intermediate places, the 

 position is oblique. 



3. A great circle of a sphere is that 

 whose plane passes through the centre of 

 the sphere ; it divides the sphere into 

 two equal parts, and has the same centre 

 as the sphere itself. The plane of a 

 small circle does not pass through the 

 centre of the sphere. 



4. Sphere, doctrine of the. An expres- 

 sion generally signifying the application 

 of the geometrical notions of the sphere 

 to geography and astronomy. It com- 

 prises an explanation of the circum- 

 stances under which spherical trigono- 

 metry is applicable to these two sciences, 

 and the nomenclature which is employed 

 to facilitate explanation. 



SPHE'RICAL {acpalpa, a sphere). Re- 

 lating to a sphere. A spherical angle is 

 an angle formed on the surface of a 

 sphere by the intersection of two great 

 circles, or circles whose planes pass 

 through the centre. A spherical triangle 

 is a triangle formed by the intersecting 

 arcs of three such circles. 



SPHERICAL EXCESS. In trigono- 

 metry, this denotes the sum by which 

 the three angles of any triangle on the 

 surface of a sphere or spheroid exceeds 

 two right angles. 



SPHERICS (a^alpa, a sphere). The 

 doctrine of the properties of the sphere 

 considered as a geometrical body, and, 

 311 



particularly, of the different circles de- 

 scribed on its surface. 



SPHEROID {<rc}iatpa, a sphere, etdo?, 

 likeness). A solid body approaching to 

 the figure of a sphere. There are two 

 kinds of spheroid, the oblate, and the ob- 

 long or prolate, the former shaped like an 

 orange, the latter like a lemon ; each 

 may be supposed to be described by the 

 revolution of a semi-ellipsis round its 

 axis, the former by the motion of the 

 semi-ellipsis round its lesser axis, the 

 latter by the ellipsis divided longwise, 

 and turned round the greater axis. The 

 earth is an oblate spheroid, being flat- 

 tened at the poles. See Ellipsoid. 



SPHERO'METER {acpalpa, a sphere, 

 imerpov, a measure). An instrument for 

 the accurate measurement of the thick- 

 ness of small bodies, the curvature of 

 optical glasses, &c. 



SPHE'RULA. A little -sphere ; a terra 

 applied to the globose peridium of some 

 fungaceous plants, having a central open- 

 ing through which sporidia are emitted, 

 mixed with a gelatinous pulp. 



SPHI'NGID^. A family of lepido- 

 pterous insects, belonging to the section 

 Crepuscularia, and named from the 

 genus sphinx, one species of which {atro- 

 pos) is the death's-head hawk-moth, of 

 considerable size, and not uncommon in 

 some parts of England. 



SPHRA'GIDE(<r0pa7i9, aseal). Lem- 

 nian earth, supposed by the Turks to 

 possess medicinal virtue; hence it was 

 dug up by them with religious ceremo- 

 nies, divided into spindle-shaped pieces, 

 and stamped with a seal. 



SPICA VIRGINIS. A star of the 

 first magnitude in the constellation 

 Virgo. 



SPIKE. A form of inflorescence, in 

 which ail the buds of an elongated 

 branch develop as flower-buds, without 

 forming peduncles, as in barley. It dif- 

 fers from a raceme merely in having its 

 flowers sessile. 



SPIKELET. Locusta. A small spike ; 

 an integral portion of the inflorescence 

 of wheat and other grasses. 



SPINE OF PLANTS. A small coni- 

 cal projection, consisting of a hardened 

 branch, sometimes bearing leaves. It 

 diflfers from the prickle in having a con- 

 siderable quantity of woody tissue in its 

 structure, and in being as much in com- 

 munication with the central parts of a 

 stem as branches themselves. 



SPINELL. Aluminate of magnesia; 

 a sub species of octohedral corundum, of 



