New Adamantine Mineral from Brazil. 187 



derate distances apart, although similar in form and position. 

 The gauge exhibited to the Society, and which was three 

 inches in diameter, and two feet in depth, was constructed 

 for me by Mr James Bryson, Princes Street, Edinburgh, 

 who has furnished several similar instruments, now in ope- 

 ration in different parts of the country. 



In conclusion, I may add, that the average annual fall of 

 rain at Aberdeen, according to six years' observations with 

 Mr Thom's gauge, was =304 inches. According to Mr 

 Thorn, the average of thirty years at Rothesay, in Bute, was 

 = 48-29 inches. The maximum annual quantity =71-37 

 inches, fell in 1811, and the minimum quantity =38-45, in 



1803. 



New College, Edinburgh, 

 June 18, 1849. 



New Adamantine Mineral from Brazil. 



M. Dufrenoy lately exhibited before the French Academy a 

 specimen of a mineral from Bi'azil, which appears to be to the 

 diamond what emery is to corundum, as stated by M. Elie 

 de Beaumont. Among some specimens recently sent to the 

 Ecole des Mines, by M. Hoffman, a dealer in minerals, were 

 two which were stated to be hard enough to polish the dia- 

 mond ; and, in fact, the hardness of these specimens was 

 found to be superior to that of the topaz. 



This substance was analysed by M. Rivot, mining- engineer, 

 who had at his disposal one large fragment weighing 65760 

 grs., and several small pieces, weighing rather less than 050 

 gr. ; the latter only were analysed. The large fragment ap- 

 peared to come from the same alluvial formation as that in 

 which the Bi'azilian diamonds occur. Its edges are rounded 

 by long friction ; but it has not the appearance of a rolled 

 flint. It is of a slightly brownish dull black colour. Viewed 

 with a glass, it appears riddled with small cavities separat- 

 ino- very small, irregular laminae, which are slightly translu- 

 cent aT>d iridescent. The brown colour is vei'y unequally dis- 

 tributed throughout the mass. On one of the faces the cavi- 

 ties are linear, which gives it a fibrous aspect similar to ob- 

 sidian. It cuts glass readily, and scratches quartz and topaz ; 

 its density is only 3-012. The small fragments subjected to 

 analysis weighed, 0-444 gr., 0-410 gr., and 0332 gr. ; their 

 densities were respectively 3141, 3-416, and 3-255. 



These numbers indicate great difference in the porosity of 

 the specimens ; they lead, however, to the conclusion, that 



