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D E X 



Binoxide. A substance in the 

 second degree of oxidation, or con- 

 taining two prime proportions of 

 oxygen : a protoxide is in the first 

 or smallest degree ; a tritoxide 

 denotes a third proportion, and a 

 peroxide has the greatest degree of 

 oxidation. 



DEVE'XITY. (devexitas, Lat.) De- 

 clivity ; a bending downwards. 



DEVOLUTION, (devolutio, Lat. dtvofa- 

 tion, Fr. devoluzidne, It.) The act 

 of rolling down, as the removal of 

 earth or strata into a valley. 



DEVO'LVE. (devolve, Lat.) To roll 

 down, as " every headlong stream 

 devolves its winding waters to the 

 main." In this sense, however, 

 the word is not modernly used: 

 in its common acceptation, at the 

 present day, it signifies to pass 

 by succession from one person to 

 another. 



DEVONIAN SYSTEM. A term assigned 

 by Sir R. Murchison to a series of 

 strata largely developed in Devon- 

 shire and Cornwall, and belonging 

 to the Old Red Sandstone. "Though 

 the term Old Red Sandstone, when 

 designating great groups of rocks 

 like the Cornish killas and Devon- 

 ian slates, should involve no error 

 of classification, still it would, 

 mineralogicall y, be most inappro- 

 priate. We purpose therefore, for 

 the future, to designate these groups 

 collectively by the name Devonian 

 system, as involving no hypothesis, 

 and being agreeable to analogy. 

 Thus the terms Carboniferous sys- 

 tem, Devonian system, Silurian 

 system, and Cambrian system, will 

 represent a vast and apparently un- 

 interrupted sequence of deposits." 

 Sedgwick and Murchison. 



DEW. A considerable refrigeration 

 of the surface of the ground below 

 the temperature of the air resting 

 upon it, amounting to 10 or 20 

 degrees, occurs every calm and 

 clear night, and is caused by the 

 radiation of heat from the earth 



into space. On becoming colder 

 than the air above, the ground will 

 condense the moisture of the air in 

 contact with it, and be covered 

 with dew. The air, however clear, 

 is never destitute of watery 

 vapour, and the quantity of vapour 

 which air can retain depends on its 

 temperature ; air at 32 being 

 capable of retaining 1-1 50th of its 

 volume of vapour, while at 52 it 

 can retain as much as l-86th. 

 That the deposition of dew depends 

 entirely on radiation is fully estab- 

 lished by the following circum- 

 stances : 1st. It is on clear and 

 calm nights only that dew is 

 observed to fall : when the sky is 

 overcast with clouds, no dew falls, 

 for then the heat which radiates 

 from the earth is returned by the 

 clouds above, and prevented from 

 radiating into space, so that the 

 ground does not become colder than 

 the air. 2nd. The slightest screen, 

 such as a cambric handkerchief, 

 stretched between pins, at the 

 height of several inches from the 

 ground, is sufficient to protect the 

 objects below it from this chilling 

 effect of radiation, and prevent the 

 formation of dew or hoar-frost upon 

 them. Plants derive a great part 

 of their nourishment from this 

 source; and as each possesses a 

 power of radiation peculiar to itself, 

 they are capable of procuring a 

 sufficient supply for their wants. 

 DEW-LAP. The loose skin which 

 hangs down under the throat of 

 the cow and other animals, and 

 thus called from its licking or 

 lapping the dew when grazing. 

 DEX'TER. ) (Latin.) The right, as 

 DE'XTEAL. ) opposed to the left. 

 In conchology, shells are divided 

 into dextral and sinistral. The 

 more common turn of shells is with 

 the apparent motion of the sun, or 

 as the index or hand of a clock 

 moves. On the contrary, a re- 

 versed, or sinistral, shell, when 



