20 Anniversary Address. 



It is stated by Mawo (Travels in Brazil) that the mines of 

 Cerro-do-Trio annually produced, between 1801 and iSOo, to the 

 amount of from 20,000 to 25,000 carats, and that the weight of 

 those sent to the Treasury in Eio Janeiro was 115,675 carats. 



As an encouragement to diamond seekers in this colony maybe 

 mentioned that numbers of the Brazilian crystals are so small 

 that four or five make only a grain, so that it takes sometimes 

 seventeen to twenty to weigh a carat. There are rarely in the 

 course of the year more than two or three of the latter weight, 

 and it takes two years to find one of 30 carats ; so that when a 

 negro workman found one of 17-| carats, called an octavo, he was 

 crowned with ilowers, conducted in triumpli to the manager, fresh 

 clad, and set at liberty. This is reported by Malte Brun ( Precis 

 iii. p. 293). Dr. Thompson has ascertained that up to 12th 

 January, 1870, 9-lOths of the diamonds at the Two-mile Plat 

 weighed less than a carat, and that 497 together weighed 120 

 carat grains ; but as they were different in size, the average is 

 assumed at one carat each, the largest being If carats. 

 One, however, had been found weighing 5-| carats. 



These facts are interesting as correlating, so far as is known, 

 the prospects of this colony and those of Brazil. 



To prevent reference to it hereafter, I may mention now that 

 a new and valuable work on precious stones (^' Handhiicli der 

 Edelstein''') was published in Vienna last year by Dr. Albrecht 

 Schrauf. I found a notice of it in the Quarterly Journal of 

 Science, for January, 1870. In it is given a formula for 

 calculating the value of -diamonds, which tested by the price 

 actually paid for the Sancy stone (£20,000), taking the Aveight 

 at 53 carats, and the price of the first carat at £15, and which is 

 near to the theoretical result ( £21,862 10s. Od.), appears to be 

 tolerably correct. It is this : — 

 m 



— (m -f 2 ) « = value, 

 2 



where m is the number of carats, and a the value of one. 



I have already noticed some of the facts stated by Messrs. 

 Heusser and Claraz. 



There are one or two others which may be quoted by way of 

 relieving the dryness of these details. But I would mention 



