DBF 



[ 70 ] 



DEN 



DEFLE'CTION. The act of turning aside 

 from its straight course ; deviation. 



DEFLE'XED. (deflexus, Lat.) In ento- 

 mology, having the sharp edge bent 

 downwards. 



DEFLE'XURE. A turning aside from a 

 straight course. 



DEGRADA'TION. (degradation, }?Y. II sig- 

 nifie deptrissement, etat de decadence, de 

 mine.} This term is used by geologists 

 to signify the lessening or wearing away 

 of rocks, strata, &c., by the action of 

 water, or other causes. 



DEGRA'DE. (degrader.fr.) To diminish; 

 to wear away ; to reduce in size. 



DEGRA'DED. Worn away ; reduced in size 

 by attrition, &c, 



DEHI'SCENT. (dehiscens, Lat.) In bo- 

 tany, fruits which open when ripe, so as 

 to enable the seeds to escape, are termed 

 dehiscent. Gaping ; opening. 



DEI'NTE GRATE. To diminish ; to separate 

 the integrant parts of. 



DELICIU'ESCE. (deliquesce, Lat.) To be- 

 come fluid by the attraction of water from 

 the atmosphere. 



DELIQUE'SCENT. That which by exposure 

 to the atmosphere attracts moisture, and 

 becomes from a solid a fluid body. 



DELL. A narrow opening between hills ; a 

 small valley. 



DELPHI'NULA. (from delpMnus, Lat.) A 

 turbinated, subdiscoidal, umbilicated uni- 

 valve. The aperture round and pearly ; 

 operculum horny. The delphinula creeps 

 on rocks and sea- weeds. This genus is 

 formed of shells formerly included by 

 Linnaeus in his genus Turbo. Lamarck 

 places delphinula in the family Scalariana. 

 The fossil delphinula occurs in the ter- 

 tiary deposits. 



DE'LTA. A term applied by geologists to 

 the alluvial deposits formed at the 

 mouths of rivers. It has obtained its 

 name from a supposed resemblance to 

 the Greek letter A. Deltas are occa- 

 sionally of immense size, and they are 

 divided into lacustrine, mediterranean, 

 and oceanic, the first being those formed 

 in lakes, as the delta at the mouth of the 

 Rhone, at the upper end of the lake of 

 Geneva ; the second, or mediterranean, 

 are those formed in inland seas, as that 

 at the mouth of the Rhone, where it 

 enters the Mediterranean ; the third, or 

 oceanic, are those formed on the bor- 

 ders of the ocean, as the delta of the 

 Ganges. 



DE'LTOID. (from delta, the fourth letter of 

 the Greek alphabet.) The name of a 

 muscle of the shoulder, from its supposed 

 resemblance to the Greek letter A ; tri- 

 angular. 



DE'NDRACHATE. (from Skvfipov and a%a- 

 r/f , Gr.) An agate with delineations of 



trees, ferns, moss, &c. Some of these 

 are exceedingly beautiful, and are so 

 elegantly depicted that they have been 

 erroneously taken for real plants, whence 

 their name. These pebbles are found 

 abundantly on the shore from Bognor to 

 Brighton, and when cut and polished, are 

 made into very beautiful necklaces, 

 brooches, snuff-boxes, &c. &c. 



DE'NDRITE. (dtvdpiTi, Gr.) The same 

 as dendrachate. 



DENDRI'TICAL. Containing the resem- 

 blance of trees, ferns, or mosses. 



DE'NDROITE. A fossil resembling the branch 

 of a tree. 



DE'NDROLITE. (from devdpov and X<0oe, 

 Gr.) Fossil wood ; the fossil branch of a 

 tree. 



DE'NSITY. (densitas, Lat. densite, Fr. den- 

 sita, It.) Closeness ; compactness ; that 

 property directly opposite to rarity, where- 

 by bodies contain such a quantity of 

 matter in such a bulk. The densities of 

 bodies are proportional to their masses, 

 divided by their volumes. Hence if the 

 sun and planets be assumed to be spheres, 

 their volumes will be as the cubes of their 

 diameters. The strata of the terrestrial 

 spheroid are not only concentric and 

 elliptical, but the lunar inequalities show 

 that they increase in density from the 

 surface of the earth to its centre. 



The absolute density of, or the quan- 

 tity of matter contained in, the earth, 

 compared with an equal bulk of any 

 known substance, may be nearly deter- 

 mined by the attractive force which any 

 given mass of matter exerts upon a plum- 

 met, when suspended in its vicinity, to 

 draw it from a vertical line. By this me- 

 thod it has been found that the mean 

 density of the earth is about five times 

 greater than that of water, or nearly 

 twice the average density of the rocks and 

 stones on the surface. The mean den- 

 sity of the ocean is only about one-fifth 

 part of the mean density of the earth. 



DE'NTAL. (dentalis, Lat. dentate, Fr. 

 dentale, It.) Relating to the teeth; re- 

 sembling a tooth, as a dental process. 



DE'NTAL. ) (from dens, Lat.) A shell- 



DENTA'LIUM. $ fish belonging, according 

 to Linnaeus, to the class Vermes, order 

 Testacea. The shell consists of one tu- 

 bulous arcuated cone, open at both ends. 

 There are many species, distinguished by 

 the angles, striae, &c. of their shells. 



The observations of Deshayes lead to 

 the conclusion that the genus Dentalium 

 approaches very closely to the molluscs, 

 if, indeed, it does not belong to them. 

 The dentalia are found in deep water, 

 frequently near the shore, inhabiting the 

 ocean only ; they are solitary. The ani- 

 mal is a terebella. The shells are known 



