DIS 



DIS 



DIPTEROCA'RPEiE. The Camphor- 

 tree tribe of Dicotyledonous plants. Trees 

 abounding in resinous juice ; leaves alter- 

 nate; flowers polypetalous; stamens hy- 

 pogynous ; carpella concrete ; calyx tu- 

 bular ; fruit coriaceous. 



DI'PTEROUS (3i?, twice, Trrepoi/, a 

 wing). Two-winged; a term applied to 

 certain s?eds which have their margins 

 prolonged in the form of wings. 



DIPTERY'GIANS (6i?, twice, Trrepu- 

 •ytoi/, a fin). A family of fishes comprising 

 those which have only two fins. 



DIPY'RE {bU, twice, irvp, fire). Leuco- 

 lite. A silicate of alumina and lime, found 

 in the western Pyrenees. This mineral 

 derives its name from its twofold sus- 

 ceptibility to the action of fire: when 

 heated before the blowpipe, it first be- 

 comes phosphorescent, and then fuses. 



DIRECT AND RETROGRADE. As- 

 tronomical terms expressive of the direc- 

 tion in which the heavenly bodies move. 

 The direct course is from west to east ; 

 the retrograde, from east to west. These 

 motions are otherwise indicated, the 

 former by the term in consequentia, the 

 latter by in antecedentia. 



DIRECTION, NUMBER OF. The 

 number of days after the 22nd of March, 

 including both days, upon which Easter 

 Sunday takes place. 



DIRECTIVE FORCE. A term em- 

 ployed in Magnetism to denote the ten- 

 dency in one magnet to assume a par- 

 ticular position with relation to another 

 magnet. 



DIRE'CTRIX. Linea directrix. A 

 term applied, in Conic Sections, to a line 

 drawn at right angles to the axis of a 

 parabola, when produced to a certain 

 point ; and this point is equally distant 

 from the vertex as the focus of the curve. 



DISC {hiaKoi, discus, a dish, or quoit). 

 The face of a circular plate ; a term ap- 

 plied to the apparently plane surface of 

 the heavenly bodies, from the resem- 

 blance of this surface to a flat round 

 dish. The discus of the ancients was a 

 circular piece of wood, stone, or metal, 

 used in their games. 



DISCHARGER. An instrument for 

 discharging a jar or battery of its elec- 

 tricity. It consists of two bent metallic 

 rods, each of them terminating at one 

 end in a brass knob, and connected at 

 the other end by a joint, which is fixed 

 to a glass handle. 



DISCO'BOLI (3/0-/COP, a disk, /3d\\w, 

 to throw). A family of Malacopterygious 

 or soft-spined fishes, in which the ventral 

 110 



fins are formed into a disk or sucker, by 

 which the fish is enabled to attach itself 

 to rocks and other hard substances. 



DI'SCOID {iKTKoeibh'iy quoit-shaped). 

 Circular or disk-shaped, and much flat- 

 tened, as the fresh-water genus planar- 

 bis, and many land-shells. 



DISCORD. Dissonance. In Music, a 

 dissonant and inharmonious combination 

 of sounds, unless treated according to 

 the rules of art. 



DISCOURSE. Discursus. In Logic, 

 an operation of the mind commonly called 

 reasoning, or the act of proceeding from 

 one judgment, to another founded upon 

 that one, or the result of it. 



DISCOVERY OF TRUTH. There 

 are two modes of discovering truth. 

 1. The one is by Information, and it 

 relates to matters of fact previously 

 unknown, but communicated by observa- 

 tion and testimony, independent of all 

 d, priori reasoning. 2. The other is by 

 Instruction, and it relates to truths which 

 may be elicited by reasoning, and are 

 therefore implied in what we already 

 know, independent of observation or 

 testimony. The historian informs, the 

 mathematician and the moralist instruct. 



DISCRETE PROPORTION {discre- 

 tus, separated). An arithmetical propor- 

 tion, in which the ratio of the antece- 

 dents to the consequents is different from 

 the ratio of the consequent of the first 

 pair of terms to the antecedent of the 

 second, as in 2 I 3 ; I 4 ; 6. On the 

 other hand, a continual proportion is 

 that in which the ratio of every contiguous 

 pair of terms is the same throughout, as 



in 2 : 4 : : 8 : le. 



DISCRETE QUANTITY (discretus, 

 separated). A quantity of which the 

 component parts have a separate and dis- 

 tinct existence : numbers, for instance, 

 are discrete quantities, being composed 

 of separate units. 



DISJU'NCTIVE. A logical term ap- 

 plied to a proposition which consists of 

 two or more categoricals, so stated as to 

 imply that some one of them must be 

 true; e.g., either A is B, or C is D. A 

 syllogism is said to be disjunctive, the 

 reasoning of which turns on such a pro- 

 position. 



DISK. A term applied, in Botany, to 

 certain bodies or projections, situated be- 

 tween the base of the stamens and the 

 base of the ovary, forming part with 

 neither. It is often incorrectly called 

 nectary. 



DISPERSION OF LIGHT. The di 



