DED 



DEF 



DECOMPOSI'TION. The resolution 

 of a body into its component parts, either 

 spontaneously or by chemical agency. 



DE'COMPOUND. A term applied, in 

 Botany, to those ramifications of plants 

 which are variously compounded, as to 

 leaves in which the petiole bears second- 

 ary petioles. When the secondary petioles 

 are divided into a third set, such leaves 

 are said to be supradecompound. 



DE'CREMENT {decrementum, a de- 

 crease). A term used in Crystallography 

 to denote a deficiency of successive layers 

 of molecules in a crystal, when this de- 

 ficiency takes place in any regular order. 

 This decrement is measured by the edges 

 of the defect or part wanting to complete 

 the simple or primary form ; and the re- 

 lation which these edges bear to the cor- 

 responding edges of the primary form, is 

 called the law of the decrement. This is 

 invariably found to be a simple numerical 

 ratio, rarely exceeding the number six. 

 The planes resulting from these decre- 

 ments are called secondary planes, and 

 the forms bounded by secondary planes 

 are secondary forms. 



Decrements in breadth are those in 

 ■which each lamina has only the height 

 of a molecule, so that their whole eflTect, 

 by one, two, three, &c., courses, is in the 

 way of breadth. Decrements in height 

 are those in which each lamina, exceed- 

 ing only the following one by a single 

 course in the direction of the breadth, 

 may have a height double, triple, quadru- 

 ple, &c., of that of a molecule: this is 

 expressed by saying, that the decrement 

 takes place by two courses, three courses, 

 &c. in height. 



DECREPITATION (decrepo, to crac- 

 kle, as a candle, when almost entirely 

 burnt). The crackling noise which oc- 

 curs when certain salts part with their 

 water of crystallization, on the applica- 

 tion of heat, and fall in pieces. 



DECU'MBENT {decumbo, to lie down). 

 Lying prostrate, but rising from the 

 earth at the upper extremity, as applied 

 to the directions taken by plants. 



DECU'RRENT (decurro, to run down) 

 Decursive. Running down ; a term ap- 

 plied, in Botany, to leaves which are pro- 

 longed down the stem, giving it a winged 

 appearance. 



DECUSSA'TTON {decusso, to cross like 

 an X). A term applied to parts which 

 cross each other, as leaves on a stem, 

 when arranged in pairs which alter- 

 nately cross each other. 



DEDUCTIVE REASONING. The 

 102 



process of scientific inquiry by which we 

 pursue laws into their remote conse- 

 quences, as distinguished from inductive 

 reasoning, by which we arrive at laws or 

 axioms by an accumulation of facts. 



DE'FERENT CIRCLE {defero, to 

 carry away). In the Ptolemaic system, 

 a circle or orbit on which the cei^re of 

 another circle or orbit is carried round. 

 Thus, the earth's orbit is a deferent on 

 which the moon's orbit is carried. See 

 Epicycle. 



DE'FINITE TERM. In Logic, a term 

 which defines, or marks out, a particular 

 class of beings, or a single person, as 

 distinguished from an indefinite term, 

 which does not define or mark out an 

 object. Thus, all animals are rational, 

 or not-rational ; the former is a definite, 

 the latter an indefinite term. Definite 

 terms are positive, indefinite terms are 

 privative or negative. 



DEFINITION. A metaphorical term, 

 literally signifying the "laying down a 

 boundary," and employed, in Logic, to 

 denote " an expression which explains 

 any term, so as to separate it from every 

 thing else," as a boundary separates 

 fields. 



A definition is called nominal, when it 

 merely explains the meaning of the term ; 

 real, when it explains the nature of the 

 thing ; essential, when it assigns the con- 

 stituent parts of the essence or nature ; 

 accidental, when it assigns the properties 

 and accidents of the essence ; physical, 

 when it lays down the real parts of the 

 essence which are actually separable ; 

 metaphysical or logical, when it lays down 

 the ideal parts of it, which cannot be 

 separated except in the mind. 



DEFLAGRATION {deflagro, to be 

 utterly consumed by fire). The oxidation 

 of metals by mixing them with nitrate or 

 chlorate of potash, and projecting the 

 mixture into a red-hot crucible. 



1. Deflagrating Mixtures. These are 

 generally made with nitre, the oxygen of 

 which is the active ingredient in pro- 

 moting their combustion. 



2. Deflagrator. The name given by 

 Dr. Hare to a very effective battery, in 

 which the plates were so connected to- 

 gether as to admit of the whole being 

 immersed into the exciting liquid, or 

 removed from it, at the same instant. 



DEFLE'CTION [deflecto, to bend off). 

 The distance by which a curve departs 

 from another curve or from a straight 

 line; or any effect of curvature or of 

 discontinuous change of direction ; also, 



