EXPLANATION OF SCIENTIFIC TERMS. 



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VARIATION OF THE COMPASS. 



See Mariner's Compass. 



VEGETABLE ALKALI. See Alkali. 



VELOCITY. See Gloss. I. 



VERNIER. See Gloss. I. 



CHROMATIC. See Gloss. I. 



VERTEX. See Cone and Conic Sections. 



VERTICAL CIRCLE. See Horizon. 



PLANE. See Horizon. 



VESUVIAN, or IDOCRASE, is a stone, 

 generally of a reddish-brown colour, simi- 

 lar in appearance to common garnet. It 

 is found, crystallized, among substances 

 thrown out of volcanoes ; and, as its 

 name indicates, particularly by Mount Ve- 

 suvius. 



VOLTAISM._See Galvanic. 



VOLTAIC BATTERY, &c. See Gal. 



VflHlC. 



VORTICES, the plural of the Latin yortev, 

 a whirlpool. The primary hypothesis of 

 the natural philosophy of Descartes was 

 that the universe is a plenum (Latin 



p/cnus, full); that is, without any vacuum, 

 or unoccupied space; and that the atoms 

 of matter moved in numerous vortices 

 which carried the heavenly bodies around 

 their several centres of motion ; such as 

 the planets about the sun, and, perhaps, 

 similar planets around the fixed stars. 



WEATHER-GLASS. The barometer is 

 popularly termed a weather-glass, because 

 its variations are commonly believed to 

 prognosticate the approaching state of the 

 weather. In former times, the same appel- 

 lation was given to the thermometer. 



ZENITH. See Horizon. 



ZIRCON is a heavy, hard, sparkling, and 

 transparent stone, susceptible of a fine 

 polish, and having a strong double refrac- 

 tion. It is usually divided into the two 

 varieties of hyacinth and jargon ; the for- 

 mer having a yellowish-red colour, and 

 the latter being most esteemed when co- 

 lourless. 



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