EXPLANATION OF SCIENTIFIC TERMS. 



perbolas, such as we may conceive to have 

 been cut from the opposite cones, repre- 

 sented in fig. 5 ; the line d a in. both 



Fig. 8. 



figures being different views of a single 

 line in the cutting plane ; and the part 

 c b cut off by the cones is here repre- 

 sented by the line A B, which joins the 

 vertices of the curves. Bisecting A B in 

 C, any right line (as p q) drawn through 

 C (which is called the centre}, and termi- 

 nating in both curves, is a transverse 

 diameter, and of all these diameters the 

 axis A B is the shortest. 



Two points g and h, in the line of the 

 Axis, equally distant from either vertex 

 of the hyperbolas, are their Foci,and these 

 are so situated that, if we take any 

 point ra, in either of the curves, and 

 draw the straight lines m g and m h, the 

 difference of the lengths of those lines 

 will be always equal to A B, the shortest 

 transverse diameter. Again, as in the 

 ellipsis and parabola, any straight line 

 mon, in either hyperbola, crossing the 

 axis at right angles, and terminating at 

 both ends in the curve, is a double Ordi- 

 nate ; m o and o n are Ordinates, and o B 

 is the Abscissa. 



The conic sections have certain pro- 

 perties in common, but the hyperbola 



possesses a peculiar one, which is often 



alluded to, and usually considered as pa- 

 radoxical: two right lines, rs and tu, 

 may be drawn through the centre C, 

 which will pass alongside of the different 

 legs of the two hyperbolas ; and although 

 continually approaching nearer and 

 nearer, these curves and straight lines, 

 however much produced, would never 

 meet each other. These lines are called 

 the Asymptotes. The opposite hyperbo- 

 las, here described, fill two angles of the 

 cross formed by these asymptotes : and 

 the two blank angles might be filled with 

 two other hyperbolas, of which y z would 



be the axis ; and the same lines, r s and 

 tu, would also be asymptotes to the new 

 curves. In such a case each opposite 

 pair would be Conjugate hyperbolas to 

 the other, and the shortest Transverse 

 diameter of the one pair would be the 

 Conjugate diameter of the other. A very 

 curious account of coloured rings, crossed 

 by opposite hyberbolic curves, is given at 

 pp. 24, 25, of the Treatise on the Pola- 

 risation of Light. 



It will be observed, that in every conic 

 section, we have pointed out two lines, 

 at right angles to each other, called the 

 Ordinate&nd the Abscissa. At whatever 

 point of the axis (in the same sort of 

 curve) the ordinate may be drawn, these 

 two lines will have always the same rela- 

 tion to one another ; and the algebraic 

 expression which points out that relation, 

 in each figure respectively, is termed the 

 Equation of that curve. From any one 

 general property of a curve, all its other 

 properties may be ascertained ; and the 

 reasoning that enables us to do so, in the 

 Ellipsis, the Parabola, and the Hyper- 

 bola, constitutes the whole of the doctrine 

 of Conic Sections. 



CONJUGATE DIAMETERS. See Co- 

 n>c Sections 



CONJUGATE HYPERBOLAS. See 

 Conic Sections. 



CONOID. A conoid is a solid which may 

 be conceived as generated by the motion 

 of a parabola or of a hyperbola round its 

 axis. Some have included the spheroid 

 in the class of conoids, but they are more 

 usually limited to the Paraboloid and 

 the Hyperboloid. See Spheroid. Conoids 

 are of various thicknesses in comparison, 

 with their height, according to the pro 

 portions of the parabola, or hyperbola, 

 by which they are generated. The 

 Solid of least resistance, spoken of at 

 page 22 of the Preliminary Treatise ^ is a 

 Conoid. 



CONVERGING RAYS are rays of light, 

 the direction of which is such that they 

 will meet or cross one another at, or near 

 to, a common centre. Their divergence 

 from that centre is termed their aberra- 

 tion. See Aberration. 



CONVEX LENSES See Lens. 



MIRRORS. See Mirror. 



CORUNDUM, or CORINDON, a stone 

 found in India and China, which, when 

 crystallized, has usually the form of a 

 six-sided prism. The diamond was for- 

 merly called Adamant ; and the crys- 

 tals of corundum, being next in hardness, 

 have the name of Adamantine Spar. The 

 Amethyst. Ruby, Sapphire, and Topaz are 

 considered as varieties of this spar, differ- 

 ing from one another chiefly in colour. 

 The amethyst is of a reddish violet co- 

 lour ; the ruby is red ; the sapphire is 

 blue, and the opaz is yellow. These are 

 termed oriental gems ; but stones having 



