DESMONCUS DIAMOND. 



273 



DESMONCUS (Martial). A genus of South 

 American palms belonging to Moncecia Polyandria of 

 Linnaeus, and to the natural order Palnue. Generic 

 character: spatha double ; flowers sitting. Males 

 calyx tritid, corolla three-petaled, stamens six. Females 

 calyx and corolla urceolate ; stigmas three, sitting ; 

 drupe one-seeded, shell having three pores in the 

 shape of a star at top. This palm thrives in loam 

 and moor earth. 



DEWBERRYis the vulgar name of the Rubus 

 caBsiun, a small trailing plant found on barren ground, 

 bearing fruit resembling those of the bramble, only 

 much smaller. 



DIADEM A (Ranzani). A genus of molluscs 

 united to the genus Coronula, of which it forms a sub- 

 division, and is there described. 



DIAMOND, a mineral body of great value and 

 hardness, first discovered in Asia. The primitive 

 form of this precious stone is the regular octoedron, 

 each triangular facet of which is sometimes replaced 

 by six secondary triangles, bounded by curved lines ; 

 so that the crystal becomes spheroidal, and then pre- 

 sents forty-eight small facets. These two peculiar 

 characters of the diamond are exhibited in the sub- 

 joined figures. 



The diamond has been found of a great variety of 

 colours, but those that are decidedly colourless, and 

 those that approach to a rose tint, are most esteemed. 



Many stones when rubbed exhibit very distinct 

 electrical effects, and they will attract or rep . light 

 bodies which are brought into their neighbourhood. 

 The diamond, when excited, exhibits positive elec- 

 tricity ; whereas the other precious stones, if rough, 

 afford negative electricity. In general, however, it 

 does not retain this electricity for any considerable 

 length of time. 



The diamond becomes phosphorescent when ex- 

 posed to the rays of the sun. Many diamonds, how- 

 ever, do not possess this property, although agreeing 

 in colour, form, and transparency, with those which 

 readily become luminous. The continuance of the 

 phosphorescence varies from five or six seconds to a 

 full hour, and this even when the stone has not been 

 exposed more than a few seconds to the rays of the 

 sun. It is phosphorescent under water, as well as in 

 the air. The diamond, when exposed to the blue 

 rays of the prism, becomes phosphorescent ; but when 

 exposed to the red rays is not so. The spark from a 

 charged jar produces the same effect as exposure to 

 the sun's rays. Exposure to the light of a wax candle 

 also produces phosphorescence. 



Prior to the commencement of the eighteenth cen- 

 tury, all the diamonds employed in Europe were im- 

 ported from the provinces of Golconda and Visapour, 

 in Bengal, and a lew from the island of Borneo. 

 They always occur in detached crystals in alluvial 



NAT. HIST. VOL. II, 



soil ; and this circumstance, no doubt, tended to give 

 currency to the fiction of the " Valky of Diamonds " 

 in the Arabian Tales. 



Diamonds of any great value in a commercial point 

 of view, were first brought from Sruth America in 

 1720, and we may now briefly point out the modes of 

 discovering them both in that country and Asia. In 

 Brazil the natives collect the disintegrated sandstone 

 met with at the bottoms of rivers and ravines, and, by 

 washing, separate the clayey matter from the grains of 

 quartz and diamond. The residue is ciref'ully examined 

 for the diamonds it may contain, which are distin- 

 guished by their adamantine lustre, ad regular forms. 

 In the district of Cuddapah, in Hind istan, the mode of 

 working the diamond mine is as follovs : After all the 

 superincumbent strata, and the large stones in the 

 diamond bed, are removed out of the mine, the small 

 gravel and other constituents of the bed are then car- 

 ried to a short distance, and put into a cistern, about 

 eight feet square, and three deep. In this situation 

 water is poured upon it, which separates the lighter 

 loamy particles. The gravel and small stones which 

 sink to the bottom, are then thrown into a heap beside 

 the cistern, from which they are conveyed to a smooth 

 plane of about twenty feet square, made of hardened 

 clay. Upon this the whole is thinly spread. The 

 gravel in this position being slightly moistened, six or 

 seven people go over it several times in succession. 

 The first time they pick out only the large stones ; 

 the second and subsequent times, the smaller gravel 

 is carefully turned over with the flat of the hand, 

 whilst they as carefully watch for the spark from the 

 diamond, which distinctly marks the situation of this 

 valuable gem. 



The locality of the diamond differs, however, in a 

 geological point of view, very considerably in different 

 parts of the world ; and, as such, the modes practised by 

 the natives for procuring these precious gems. Thus 

 we find that the diamond mines, as they are called, 

 situated at Banaganpilla, are scarcely any thing more 

 than holes in the surface of the soil. None are deeper 

 than twenty feet, and when a gallery is excavated 

 under the rock, it is so low that the people are obliged 

 to work in it sitting, a mode of operating which an 

 Indian prefers to every other. The solid rock of the 

 hills is an agate, consisting chiefly of a coarse grey 

 hornstone, with rounded pebbles of the same species, 

 or of jasper. At some depth, this rock becomes a 

 ferruginous sandstone, the grains of which are finely 

 cemented together. Through this solid rock they are 

 obliged to make their way before they arrive at the 

 bed in which the diamonds are usually found. They 

 commence at different places as their fancy leads them, 

 with a spot about twenty feet square, which, with iron 

 instruments and steel wedges, they break into slabs 

 and fragments, of from one hundred to five hundred 

 pounds weight. In this way they descend to the 

 diamond bed, which is fifteen or twenty feet under 

 the surface ; this bed extends round the whole hill, 

 and is as regular in its thickness and extent as the 

 unproductive beds in the same place : it consists of a 

 conglomerate, composed of siliceous pebbles, quartz, 

 calcedony, and jasper. 



The diamond, on account of the splendour of its 

 lustre, its peculiar play of colour, its hardness, and 

 lastly, its rarity, is considered as the most precious 

 substance in the mineral kingdom, and is particularly 

 valued by jewellers. The diamonds purchased by 

 jewellers are generally in grains or crystals, and some- 

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