Chap, 44.] fbe Diamond. 183 



above a certain fize. The fovereigns of India refervc 

 the largeft, in order that the price of this article may 

 not fall. Diamonds have no brilliancy when dug out 

 of the earth, but are covered with an earthy cruft, which, 

 inclofes a feconcl cruft, of the nature of calcareous fpar, 

 according to M. Rome de Lifle. Bright diamonds arc 

 occafionally found in waters. 



Thefe gems very often have no regular form, but are 

 flat; or worn round, Sometimes they are regularly 

 cryftallized in octahedrons, formed by two quadran- 

 gular pyramids, united at their bafe ; they are likewife 

 found with twelve, twenty-four, and forty-eight faces. 



Diamonds appear to be compofed of laminae, laid 

 upon each other ; and they are eafily divided, by itrik- 

 ing them in the direction of thefe laminse with a good 

 fleel instrument. There are, however, fome diamonds 

 which do not appear to be formed of diftinct laminse, 

 but of twifted fibres, like thofe of knots in wood. 

 Thefe laft are exceedingly hard, and cannot be wrought; 

 lapidaries call them diamonds of nature. 



Diamonds are (haped by firfl cleaving them in the 

 direction of their lamellae, and then rubbing them 

 with other diamonds. They are then po'imed by an 

 horizontal fleel wheel, dufted with their own powder 

 mixed with olive oil. 



Sir Ifaac Newton having obferved that inflammable 

 fubftances had a ftronger power of refracting the rays 

 of light, in proportion to their denfities, than other 

 bodies, and obfcrving alfo the ftrong refractive power 

 of the diamond, conjectured, upon thefe principles, 

 that it mufl belong to this clafs of minerals. The 

 reafonings of Newton were fo correct, that many of 

 his conjectures, though made only on theory, have 

 been fince confirmed by actual experiment. Thus it 

 has fince been difcovered that diamonds, expofed to 



a high 



