DEL 



DEN 



the bending of a ray of light from its 

 rectilinear course towards an opaque body 

 in its immediate neighbourhood. See 

 Diffraction. 



DEGLUBITRI'CES {degluho, to pull 

 off the skin or rind). Huskers ; the name 

 given by Macgillivray to ati order of birds 

 •which remove the shell or husk of seeds 

 in their bill, before swallowing them. 

 They are all easily recognized by their 

 stout conical bill, and include all our 

 small finch-like birds. Most of them have 

 a modulated song, which is, however, 

 much inferior to that of the Cantatrices. 



DEGRADING CAUSES. A term ap- 

 plied, in Geology, to those causes which 

 refer to the dissolving and wearing away 

 of the elevated parts of the earth's sur- 

 face, and the carrying of these parts 

 down into lower levels. These causes 

 are meteoric, connected with the atmo- 

 sphere ; fluviatile, depending on rivers ; 

 and oceanic, in which the ocean is the 

 immediate agent. 



DEGREE, MINUTE, SECOND. The 

 circumference of every circle, whatever 

 be its actual dimensions, is usually con- 

 sidered as consisting of 360° (degrees), 

 each of which is divided into 60' (minutes), 

 each of these again into 60" (seconds), and 

 so on to thirds {"'), and fourths (""), and 

 fifths, if necessary, each term being a six- 

 tieth of its predecessor. By some writers 

 the decimal system is preferred. 



DEGREE, IN ALGEBRA. The de- 

 gree of an algebraical term is the number 

 of letters which enter into it as factors ; 

 thus a?2y3 is absolutely of the fifth de- 

 gree, but of the second degree with re- 

 gard to X, and of the third degree with 

 regard to y. The degree of an equation 

 is the power of its highest term ; if the 

 index of this term be 4, the equation is 

 said to be of the fourth degree. 



DEHI'SCENCE {dehisco, to gape). A 

 term applied, in Botany, to the sponta- 

 neous separation of the valves of the 

 fruits of certain plants, for the discharge 

 of the seeds ; and, in Zoology, to the 

 splitting open of the bag w^hich contains 

 the eggs. 



DEINOTHE'RIUM (deivov Onpiov, a 

 terrible beast). A fossil genus of gigantic 

 pachydermata, characterized by the down- 

 ward projection of enormous tusks from 

 the loweir jaw. 



DE'LIAN PROBLEM. A celebrated 

 problem, proposed by the oracle at Delos, 

 and known to geometers as the duplica- 

 tion of the cube. 



DELIQUE'SCENCE {deliquesco, to 

 103 



melt away). The property of certain 

 salts of becoming liquid by their attract- 

 ing moisture from the atmosphere. In 

 Botany, a panicle is said to be deli- 

 quescent, when it is so much branched 

 that the primary axis disappears— seem- 

 ing, as it were, to melt away. 



DELPHI'NIDiE (delphinus, a dol- 

 phin). The Dolphin tribe ; a family of 

 the cetaceous Vertebrata, distinguished 

 from the Balsenidae, or Whale tribe, by 

 the relative size of the head and body : 

 in the former, the head is not out of the 

 usual proportion ; in the latter, it is im- 

 moderately large. 



DELPHI'NUS. The Dolphin ; one of 

 the old Greek constellations, consisting 

 of eighteen stars, and succeeding Aquila 

 in the heavens. 



DE'LTA (3e\Ta, the Greek letter A). 

 A term applied to the alluvial land 

 formed by a river at its mouth, when it 

 divides, before entering the sea, into 

 separate and diverging streams. The 

 term was first applied in the case of the 

 Nile, from the resemblance of the alluvial 

 land to the form of the Greek letter A, 

 the sea forming the base of the triangle ; 

 but geologists employ the term in analo- 

 gous cases, without reference to the pre- 

 cise shape. 



DE'LTOID (ae\TO€t3^?, delta-shaped, 

 triangular). Shaped like the Greek letter 

 A ; a term applied to a solid, the trans- 

 verse section of which has a triangular 

 outline. 



DEMONSTRA'TION {demonstro, to 

 point out). In the old writers, this term 

 signified no more than the pointing out 

 the connexion between a conclusion and 

 its premises, or that of a phenomenon 

 with its asserted cause. It now denotes 

 a necessary consequence, and is synony- 

 mous with proof. 



DEMO'TIC WRITING {dnfioriKSi, of 

 the people). A mode of writing in com- 

 mon use among the Egyptians, approach- 

 ing very nearly to the Chinese method. 

 It is also termed the epistolographic and 

 the enchorial style. 



DE'NEB. An Arabic term for tail, 

 generally applied to the bright star (/3) in 

 the tail of Leo. 



DENO'MINATOR. An arithmetical 

 term, employed in fractions, to denote 

 the number of parts into which the unit, 

 or integer, is divided. The other part of 

 the fraction, or the numerator, denotes 

 how many of these parts are taken to 

 make up the given fraction. 



DE'NSITY {densitas, closeness). A 

 f 4 



