DEW 



DI A 



Literally, the throwing off of froth or 

 scum, and generally, the clarifying of a 

 fluid, or the separating its foul parts. 



DESQUAMA'TION {desguamo, to scale 

 fishes, to bark trees). The falling off of 

 the cuticle, in the form of squamce or 

 scales. 



DETER'MINATE PROBLEM. A 

 problem which admits of one solution 

 only, or of a limited number of solutions ; 

 as distinguished from an indeterminate 

 problem, which admits of an indefinite 

 number of solutions. 



DETONATION {detono, to thunder 

 mightily). Instantaneous ignition, ac- 

 companied by a loud noise and a violently 

 disruptive force, owing to the sudden 

 expansion of gas. 



DETRITUS {de, from, tero, to rub). 

 Matter worn or rubbed oflf from rocks, 

 consisting of blocks of various sizes, 

 gravel, sand, and clay. 



DEUTO- (3ewT€po9, second). A prefix 

 denoting two, or double, as deut-oxide, 

 having two degrees of oxidation ; deuto- 

 chloride, &c. 



DEUTOXIDE (aeurepo?, second). A 

 term applied to a substance which is in 

 the second degree of oxidation. This term 

 is often used to denote a compound of 

 3 atoms of oxygen with 2 of metal, as in 

 deutoxide of manganese, of lead, &c. 



DEVE'LOPMENT. In Algebra, the 

 process by which any mathematical ex- 

 pression is changed into another of equi- 

 valent value or meaning, and of more 

 expanded form. 



DEVONIAN SYSTEM. A geological 

 system, comprising the old red sandstone, 

 and forming the material of the grand 

 and rugged mountains which fringe many 

 parts of our Highland coasts, and range, 

 on the south flank of the Grampians, 

 from the eastern to the western sea of 

 Scotland. These formations, in Devon- 

 shire and Cornwall, abound in shells and 

 corals, and present a structure which 

 brings them into a mineralogical com- 

 parison with our older slate rocks. 



DEW. The moisture insensibly de- 

 posited from the atmosphere on the sur- 

 face of the earth. It occurs whenever 

 that surface is lower in temperature than 

 that of the dew-point of the atmosphere 

 immediately in contact with it. 



DEW-POINT. That temperature of 

 the atmosphere at which its moisture be- 

 gins to be precipitated. By some, it is 

 called the point of saturation ; by Daniell, 

 the degree of " the constituent tempera- 

 ture of atmospheric vapour." 

 105 



DEXIA'RIiE. A family of Dipterous- 

 insects of the section Creophilae, named 

 from the genus dexia, and subsisting 

 chiefly on the juices of flowers. 



DEXTRAL {dexter, the right hand). 

 On the right hand, as applied to the 

 mouth or aperture of the great majority 

 of spiral shells*, when the mouth is on 

 the left, it is said to be sinistral or re- 

 versed. No generic distinctions can, 

 however, be founded on this character. 



DEXTRIN {dexter, the right hand). 

 Mucilaginous starch, prepared by boil- 

 ing a solution of starch with a few drops 

 of sulphuric acid. Its name is derived 

 from its property of turning the plane of 

 the polarization of light to the right 

 hand. 



DIA {8id). A Greek preposition, de- 

 noting through. Words compounded 

 with 8ia imply extension, perversion, 

 transition ; also that which in English 

 and Latin is expressed by the preflxes 

 di- or dis-, as in divido, to divide ; dis- 

 jungo, to disjoin. 



DIACAU'STIC (3m, through, Kava-ri- 

 Kof, burning). A term applied to those 

 caustic curves, which are formed by re- 

 fraction, as distinguished from the cata- 

 caustic curve, which is formed by reflec- 

 tion. See Caustic curve. 



DIACOU'STICS {&iaKova), to hear 

 through). That branch of physics which 

 treats of the properties of sound refracted 

 in passing through media of different 

 densities. 



DIACRFTIC MARKS {dtaKptrtKdi, fit 

 to distinguish). Marks employed, in 

 Palaeography, to distinguish letters which 

 are similar in form ; thus, in the German 

 running hand, the letter u is distin- 

 guished by the superposition of the mark 

 " from the letter n. 



DIADE'LPHIA {Bk, twice, i5eX06f, 

 a brother). The seventeenth class of 

 plants in the system of Linnaeus, cha- 

 racterized by the union of the filaments 

 into two parcels, or brotherhoods. See 

 Adelphia. 



DI.E'RESIS (3m£pew, to divide). A 

 division ; a grammatical figure, denoting 

 the division of one syllable into two, as 

 siliice for silvce. 



DIAGO'METER, ELECTRICAL (a^d- 

 yo), to conduct, fserpov, a measure). An 

 apparatus used by Rousseau for ascer- 

 taining the conducting power of oil, as 

 a means of detecting its adulteration. It 

 consists of one of Zamboni's dry piles, 

 and a feebly-magnetized needle, moving 

 freely on a pivot. The deviation of the 

 F5 



