J A D 



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JAN 



IJ 



JA'DE. The Nephrit of Werner; 

 Nephrite of Jameson ; called also 

 nephritic stone, nephrite, and axe- 

 stone. It was formerly much cele- 

 brated for its supposed medicinal 

 properties in nephritic affections, 

 or diseases of the kidneys. It is 

 found in Hungary and Siberia, 

 America, Egypt, and China. The 

 inhabitants of New Zealand form 

 it into axes, and other cutting in- 

 struments, from which circumstance 

 it has obtained the name of axe- 

 stone. Its surface is smooth; 

 fracture splintery. It has a greasy 

 feel. Colour, dark leek green. In 

 hardness, jade is, at least, equal to 

 quartz ; it possesses a peculiar te- 

 nacity, which renders it difficult 

 either to break, cut, or polish. 

 Brochant states its fresh fracture 

 to present a paler green than that 

 of its surface. Before the blow- 

 pipe it fuses easily, and with a 

 slight ebullition, into a bead of 

 white semi-transparent glass. Its 

 analysis is very variously given by 

 different authors; its constituents 

 are, according to some, silica, carbo- 

 nate of magnesia, alumina, and car- 

 bonate of lime; others add chrome, 

 oxide of manganese, soda, and po- 

 tassa. In consequence of its tena- 

 city, it has been wrought into 

 chains and other delicate works. 



JAMB. A term used by miners for a 

 thick bed of stone which pre- 

 vents their pursuing a vein. 



JA'MESONITE. A mineral, thus named 

 after Prof. Jameson, by Haidinger; 

 axotomous antimony-glance. It 

 was first discovered in Cornwall, 

 in clay- si ate, and it has since been 

 found in Germany and Siberia. 

 Its colour is steel-grey. It con- 

 sists of lead, antimony, sulphur, 

 and iron. 



JANTHINE. | (from ianthwn, Lat. a 

 JA'NTHINA. j violet.) The violet 

 snail. A purple-coloured univalve 

 shell, nearly resembling a snail in 

 its form : it is recent, and com- 

 monly found in the Mediterranean. 

 The inhabitant of this shell is said, 

 when irritated, to discharge a pur- 

 ple secretion. The Janthina was 

 considered a helix until the time of 

 Lamarck, who placed it in a distinct 

 genus. He ascertained that the 

 inhabitant of this shell differed es- 

 sentially from the snail. The organ 

 which, in the snail, would consti- 

 tute a foot, is, in the janthina, 

 formed for swimming, not for 

 crawling. 



JA'NTHINA PEAGILIS. A species of 

 janthina. Sir C. Lyell remarks, 

 "janthina fragilis has wandered 

 into almost every sea, both tropical 

 and temperate. This common 

 oceanic shell derives its buoyancy 

 from an admirably contrived float, 

 which has enabled it not only to 

 disperse itself so universally, but 

 to become an active agent in dis- 

 seminating other species, which 

 attach themselves, or their ova, to 

 its shell. Principles of Geology. 



According to the account given 

 by Bosc, the janthina exhibits many 

 remarkable peculiarities. When 

 the sea is calm, these animals may 

 be seen collected often in large 

 bands, swimming over the surface 

 by means of a floating apparatus 

 consisting of aerial vesicles pro- 

 duced by their foot. During this 

 action their head is very prominent, 

 and the foot or line of vesicles forms 

 an angle with the middle of the 

 shell. When the sea is rough, the 

 animal absorbs the air from its 

 vesicles, changes the direction of 

 its foot, contracts its body, and lets 



