EXPLANATION OF SCIENTIFIC TERMS. 



COMPASS, VARIATION OF. See fa- 

 rmer's Compass. 

 COMPOSITION OF FORCES. See 



Forces. 

 COMPRESSIBILITY. See Gloss. I. 



CONCAVE MIRRORS See Mirrors ^ 



LENSES. See Lenses. 



CONDENSATION. See Gloss. I. 



CONDUCTORS OF CALORIC. See 

 Gloss. I. 



IN ELECTRICITY. If 



a body be over-saturated with the electric 

 fluid, that fluid will endeavour to escape 

 into other bodies ; or, if under-saturated, 

 the body will attract the fluid from other 

 bodies. If the positively, or negatively, 

 electrified body be surrounded by other 

 bodies through which the fluid cannot 

 pass, it is said to be insulated, to be in 

 a state of insulation ; and substances 

 which thus oppose the egress or ingress 

 of the fluid are said to be Non-conductors. 

 Those through which the passage is un- 

 obstructed are Conductors. 



CONE. See Gloss. I. 



CONJUGATE DIAMETERS. See Gloss. 

 I. in Conic Sections. 



HYPERBOLAS. See 



Gloss. I. in Conic Sections. 



CONOID. See Gloss. I. 



CONSECUTIVE POLES. See Magnet. 



CONSEQUENTS. See Ratio. 



CONVERGING RAYS. See Aberration. 



CONVEX LENSES AND MIRRORS. 

 See lenses and Mirrors. 



CORUNDUM. See Gloss. I. 



CRYSTALLIZATION. See Gloss. I. 



CUBIZITE. See Anakime. 



CURVE AND CURVATURE. See 

 Gloss. I. 



CURVES, EVOLUTES, AND INVO- 

 LUTES. See Gloss. I. 



, EQUATION OF. See Gloss. I. 



, MAGNETIC. See Magnetism. 



CURVILINEAL. See Gloss. I. 



CYANOMETER, an instrument invent- 

 ed by Saussure, for comparing the dif- 

 ferent shades of blue, of which a good de 

 scription is given in Optics, pp. 65, C6. 



CYCLOID. See Gloss. I. 



CYLINDER. See Gloss. I. 



D'ALEMBERT'S PRINCIPLE. See 

 Principle, &c. 



DEAD LEVEL. See Level. 



DECAMETRE. See Metre. 



DECARBONIZATION. See Carbon. 



DECIMETRE. See Metre. 



DEGREES AN D MINUTES. See Angle. 



DENSITY (Latin densitot, closeness) is a 

 relative term, and denotes the compara- 

 tive quantity of matter in different bo- 

 dies, which is contained in the same space 

 (see Fblumej. Gravity is understood to 

 act in proportion to the relative quantity 

 of the matter of bodies ; and, hence, the 

 specific gravities of bodies are presumed 

 to be the measure of their densities. See 

 Gravity. 



DE-OXIDATION is the depriving a sub- 

 stance of the oxygen, or vital air, which 

 it contains. Concerning the de-oxidizing 

 power of the solar rays, see Optics, 

 p. 29. 



DESCARTES'S OVALS. See Ovals of 

 Descartes. 



DIAGONAL, in geometry, is a straight 

 line, drawn through a figure from one 

 corner to another. A four-sided figure 

 has two diameters, which, when the angles 

 are right angles, are equal. 



DIAMETER OF A CIRCLE, a right 

 line passing through the centre, and ter- 

 minating at both ends by the circumfer- 

 ence. 



DIAMETERS, TRANSVERSE AND 

 CONJUGATE. See Conic Sections. 



DIAPHANOUS (from the Greek dia, 

 through, and phaino, to shine) is that 

 quality of a substance which allows a pas- 

 sage to the rays of light. Translucent is 

 a more ordinary term, of the same im- 

 port. Transparent rises above translucent, 

 by admitting not only the passage of light, 

 but the vision of outward objects. Semi- 

 translunent and semitransparent are occa- 

 sionally written to express weaker degrees 

 of those qualities. 



DIFFRACTION, or INFLEXION OF 

 LIGHT. Light, when it meets with no 

 obstacle, proceeds in straight lines ; but, 

 if it be made to pass by the boundaries of 

 an opaque body, it is turned from its rec- 

 tilineal course, which deviation is termed 

 diffraction, or inflexion. See Newton's 

 Optics, p. 10. 



DIGESTER, a strong vessel of iron or 

 other metal, having a screwed-down and 

 air-tight lid, into which animal or other 

 substances are inclosed immersed in wa- 

 ter, and submitted to a higher degree of 

 heat than could be had in open vessels, 

 whereby the solvent power of the water is 

 so increased that bones (for which it was 

 originally invented) are converted into a 



DIOPTRICS is that division of the science 

 of optics which treats of the refraction of 

 light. 



DIPPING NEEDLE, a magnetic needle 

 poised so as to move freely in a vertical 

 direction, points downward, or dips, less 

 or more, towards the earth ; except it be 

 situated on some part of a line which 

 surrounds the globe, and is called the 

 magnetic equator. On this line the needle 

 remains horizontal. This equator, which 

 intersects the geographical equator at an 

 angle of about twelve degrees, has its 

 magnetic poles at a short distance from the 

 true poles of the earth. 



DIRECT PROPORTION, or DIRECT 

 RATIO. See Ratio. 



DIRECTION, LINE OF. See Force, 

 Direction of. 



DIRECTIVE FORCE, in magnetism,is 

 the tendency in one magnet to assume a 



