13 



EXPLANATION OF SCIENTIFIC TERMS. 



certain height ; but which would be forced 

 open before the strain could burst the 

 boiler. 



SAPPHIRE. See Corundum. 



SATURATED SOLUTION. See Solu- 

 tion. 



SCALE, a line divided into a marked num- 

 ber of small and equal parts, which is ap- 

 plied to the measure of other lengths that 

 are not so divided; and thereby to ascer- 

 tain their relative dimensions. The com- 

 mon measures of length are divided into 

 feet, inches, &c., but are not termed 

 scales ; this being the scientific designa- 

 tion. The scales of thermometers have 

 a certain point from which the heat is 

 counted upwards and downwards, that 

 point being marked with a cypher, and 

 termed zero. The Latin plural, scala, is 

 a ladder which is descended by degrees 

 (degre&sus) or steps, 



SCREW, one of the mechanical powers. 

 See Mechanical Powers. 



SEAL, HERMETIC. See Hermetic 

 Seal. 



SECANT. See Angle. 



SILEX is an opaque stone, sufficiently hard 

 to scratch glass, sparkling, but never 

 crystallized. Common flint and light- 

 coloured pebbles are wholly of this earth, 

 which are termed Siliceous. It also forms 

 the basis of chalcedony, cornelian, jasper, 

 and many other stones. 



SINE. See Angle. 



SINES, LAW OF THE. See Reflective 

 Power. 



SOLIDS are bodies, the cohesion of whose 

 particles are so strong, that they are 

 moveable only as a combined mass. See 

 Fluids, and Liquids. 



SOLID OF LEAST RESISTANCE. 

 See Conoid. 



SOLUTION. A solution, in chemical 

 language, is any fluid which contains 

 another substance dissolved and inti- 

 mately mixed with it. When the fluid 

 will dissolve no more of the substance, 

 but allows the excess to deposit on the 

 bottom of the vessel, it is. said to \>esatu- 

 vated (Latin satur, full), and the mixed 

 fluid is then a Saturated Solution of the 

 substance which it contains. 



SOUND, a sensation communicated through 

 the ear, by means of the particles of air 

 (and, occasionally, other fluids) which are 

 impelled by the vibrations of the sound- 

 ing body. 



RAYS -OF. See Reflexion. 



SPAR. There are a great number of 

 ie broken surfaces of which pre- 

 hed shining plates, placed so as 

 'ach other, like horizontal beds, 

 these have been called spars , 

 brm is termed the sparry tex- 

 ture. 



>AMANTINE. See Corun- 



LAND. See Calcareous Spar, 



SPECIFIC denominates any property that 

 is not general, but is confined to an indi- 

 vidual or species. 



GRAVITY. See Gravity, 



Specific. 



HEAT. See Caloric, Specific. 



SPECTRA, OCULAR.See Ocular Spec- 

 tra. 



SPECTRUM, PRISMATIC. See Pris- 

 matic Spectrum. 

 SPECULUM. See Mirror. 

 SPHERE, or GLOBE. A sphere is a 

 solid, every point of the surface of which 

 is equally distant from a single point 

 within it, which is its centre. It is con- 

 ceived to be formed by the motion of a 

 semicircle round the diameter. 

 SPHERICAL ABERRATION. See 



Aberration, Spherical. 

 SPHEROID. There are two species of 

 spheroids, the oblate and the oblong, both 

 of which are understood to be formed 

 from the circular motion of a semi-ellipsis 

 round its axis. The oblate spheroid is 

 shaped like an orange, and the oblong 

 like a lemon. The former is generated 

 by the motion of the semi-ellipsis round 

 its lesser axis, and the latter by the ellip- 

 sis divided longwise, and turned round 

 the greater axis. These solids are ge- 

 nerally called ellipsoids, and sometimes 

 conoids, though they have no resemblance 

 to single cones, and but little to double 

 ones. The earth is an oblate spheroid, 

 being flattened at the poles. 

 SPIRAL. A spiral is a curve which turns 

 round like a circle, but instead of ending 

 where it began, it continues to revolve, 

 receding farther and farther from the 

 centre. There are various species of 

 spirals. The power that moves a watch 

 is a spiral spring. 

 STATICAL. See Statics. 

 STATICS is that division of the science of 

 mechanics which considers bodies as in- 

 fluenced by forces that are in equilibrium. 

 It is formed from the Greek statas, stand- 

 ing still. See Force and Equilibrium. 

 What belongs to Statics is Statical. 

 STEELYARD, OR ROMAN BA- 

 LANCE See Balance. 

 STEAM is the vapour of water raised to a 

 high degree of elasticity by means of heat, 

 so as to be applied, in mechanics, as a mov- 

 ing power. In ordinary language, it is 

 confounded with vapour. 

 STEAM-TIGHT denotes such a degree of 

 closeness as prevents the escape of steam. 

 STRAIGHT LINE, the same as a right 



line. See Curve. 



SUCTION. The action of sucking is per- 

 formed by the child's making a vacuum 

 in its mouth, which exhausts the air from 

 the pores of the nipple ; and the milk is 

 consequently ejected from the breast by 

 the unresisted elasticity of the air within. 

 The raising of liquids through a tube, by 

 means of a pistoa which lifts and sustains 



