23 



"Hope," the green -'Dresden," and tlxe yellow "Austrian," were 

 exhibited. 



The geographical distribution of diamonds was traced upon a 

 map, and the principal localities — the East Indies, Brazil, and 

 South Africa — were described in detaU. The history of the dis- 

 coveries in South Africa was especially dwelt upon, and a large map 

 of the district was exhibited ; while the methods of working and 

 washing the diamonds in Brazil were illustrated by scenic diagrams. 



The Lecturer then gave a sketch of the history of our know- 

 ledge of the chemical composition of the gem, referring first to the 

 early experiments of Boyle, of the Florentine Academicians, and 

 of the Emperor Francis I. Until Bergman's researches in 1777, it 

 was generally believed that diamond was a kind of rock-crystal, 

 but he first showed that it contained no silica. Afterwards 

 Lavoisier, with some other French chemists, demonstrated that the 

 gem is carbon, practically pure. In concluf?ion the Lecturer des- 

 cribed the various attempts which have been made, from time to 

 time, to induce carbon to crystallise artificially in the form of 

 diamond, and to assume the other physical properties of the gem. 

 The recent investigations of Mr. J. B. Hannay, of Glasgow, were 

 described, and reference made to his papers " C)n the Artificial For- 

 mation of the Diamond," as published in the Pn:ceedings of the 

 Royal Society (Vol. XXX, pp. 188, 450.) 



A large series of models in paste, ilhistratiug the principal 

 diamonds in the world, had been lent t<> the Lecturer by 

 Mr. E. W. Streeter, of New Bond Street : and were exhibited 

 and explained at the conclusion of the discourse. 



