BIS 



DI V 



vision of a ray of white light into its vari- 

 ously coloured component rays, as seen 

 upon the spectrum, after it has under- 

 gone refraction by transmission through 

 a prism. 



DISSE'PIMENT {dissepio, to sepa- 

 rate). Septum. A term applied, in Bo- 

 tany, to the partition which divides a 

 capsule into cells. 



DISTANCES, LAW OF. A curious 

 law observed by Professor Bode, of Ber- 

 lin — that the intervals between the planet- 

 ary orbits go on doubling as we recede 

 from the sun, or nearly so. This law was 

 interrupted between Mars and Jupiter, 

 but the deficiency was afterwards strangely 

 supplied by the discovery of four new 

 planets in that very interval, revolving 

 in orbits tolerably well corresponding 

 with the law in question. 



DISTHENE. Cyanite. A very hard 

 crystallized mineral, consisting of sub- 

 silicate of alumina. 



DI'STICHOUS (3i9, twice, (tt/xo?, a 

 row). Arranged in two rows, as the 

 florets of many grasses ; a term synony- 

 mous with bifarious. 



DISTILLATION {distillo, to drop by 

 little and little). The vaporization and 

 subsequent condensation of liquids, by 

 means of a retort, alembic, or still. Dry 

 distillation is performed in the same 

 way as the humid, except that the sub- 

 stance is neither immersed nor dissolved 

 in any menstruum. It is termed sub- 

 limation. 



Distillation, Destructive. The process 

 of exposing organized substances, or 

 their products, to distillation, until the 

 •whole has undergone the entire eflfects of 

 the furnace. 



DI'STOMA (ale, twice, crofia, the 

 mouth). Intestinal worms with two 

 pores, 



DISTRA'CTILE {distraho, to draw 

 apart). In Botany, a connective which 

 separates into two unequal portions, the 

 one supporting an anther, the other with- 

 out an anther, as in salvia. 



DISTRI'BUTED. An epithet applied, 

 in Logic, to a term which is employed in 

 its full extent, so as to comprehend all 

 its significates— every thing to which it 

 is applicable. 



DIST^RTBU'TION OF HEAT. A 

 term expressive of the several ways by 

 which the rays of heat, as they fall upon 

 the surface of a solid or liquid body, may 

 be disposed of. 1. They may be reflected, 

 or rebound from the surface ; 2. they 

 may be absorbed, or received into the 

 111 



substance of the body ; or, 3. they may 

 be transmitted, or pass directly through 

 its substance. In the first and third 

 cases, the temperature of the body on 

 which the rays fall is entirely unaffected ; 

 in the second, it is increased. 



DI'THYRA (dif, twice, Ovpa, a door). 

 A term applied by Aristotle to the bi- 

 valved moUusca, or those which have 

 double shells, as the oyster and the 

 cockle. These comprise the first order 

 of Cuvier's Acephala, the seventh order 

 of his Gasteropoda, and the fifth class of 

 his MoUusca. See Monothyra. 



DIU'RNA {diurnus, daily). A desig- 

 nation of the Butterfly tribe of Lepido- 

 pterous insects, from their habit of ap- 

 pearing only by day. They are distin- 

 guished by the vertical position of their 

 wings during repose. The tribe corre- 

 sponds with the Linnaean genus Papilio. 



DIU'RNAL MOTIO'S {diurnus, daily). 

 The daily revolution of the earth upon 

 its axis, which produces day and night, 

 and causes us to imagine that the sun, 

 planets, and stars, move round the 

 earth. See Axis. 



DIURNA'TION (diurnus, daily). A 

 term introduced by Dr. M. Hall, to ex- 

 press the state of some animals, as the 

 bat, during the day, as contrasted with 

 their activity at night. See Hybernation. 



DIVA'R I GATING (divarico, to spread 

 one from another). Spreading out nearly 

 at a right angle from any thing, as 

 branches from a stem. 



DIVERGENT RAYS. Those rays, 

 which, proceeding from a point of the 

 visible object, are dispersed, and con- 

 tinually depart one from another, in pro- 

 portion as they are removed from the ob- 

 ject ; in which sense they are opposed to 

 convergent rays. 



DIVERTI'CULUM. The Latin term 

 for a by-road, and hence applied to a 

 blind tube branching out from the course 

 of a longer one. 



DIVISIBI'LITY {divido, to divide). 

 The property by which bodies are capable 

 of being separated into minute parts. 

 The divisibility of matter, though mathe- 

 matically illimitable, is closely connected 

 with its constitution, and must, therefore, 

 cease with the ultimate particles of which 

 all matter is supposed to consist. 



DIVI'SION. In Arithmetic, the me- 

 thod of finding how often one number is 

 contained in another, i. e. how often one 

 number must be taken to make up an- 

 other. Hence Division bears the same 

 relation to Subtraction, as Multiplication 



