544 PHILOSOPHICAL TRANSACTIONS. [aNNO 1748. 



one of their meetings, and afterwards published them in N" 476 of the Philos. 

 Trans. Among these Brasilian diamonds, one was of the absolute weight of 

 92,425, another of 88,21; and among the East-Indian ones, one of 92,525 

 Troy grains. And as the size of these stones made them much fitter for these 

 inquiries, than any others which had probably ever before been used for the same 

 purpose, so the known accuracy of the author, the goodness of his instruments, 

 and the consistency of all his experiments, sufficiently show that the s})ecific gra- 

 vities he has delivered in his paper, may entirely be depended on. The same 

 curious person also communicated the specific gravities of fine and standard gold, 

 published under his name in the following tables, and which were deduced from 

 experiments he was so kind as to make on purpose at Dr. D.'s request. 



Having occasion to mention diamonds. Dr. D. observes, it may possibly not 

 be foreign to the purpose here to take some notice of the diamond carat 

 weight, used among jewellers, which weight was originally the carat or 144th 

 part of the Venetian ounce, equal to 3.2 Troy grains, but which is now, for 

 want of an acknowledged standard, somewhat degenerated from its first weight. 

 He had himself found it, on a medium of several experiments, equal to 3.1 7 Troy 

 grains; and he had the rather taken notice of this weight here, because there 

 happens to be a mistake about it, both in Dr. Arbuthnot's and Mr. Dodson's 

 tables, who have set down as it seems the number of diamond carats in a Troy 

 ounce, instead of the weight of the diamond carat itself. This carat is again 

 divided into 4 of its own grains, and those into halves and quarters, commonly 

 called the 8ths and l6ths of a carat; and thus the largest of the diamonds just 

 abovementioned, weighed, in the jewellers' phrase, better than 29 carats and al- 

 most half a grain. 



Mr. James Dodson, in his book called The Calculator, printed in 8vo at 

 London in 1-747, has inserted a useful table of specific gravities, in which he has 

 by the first initial letter of their names distinguished the several authors he has 

 quoted; and among these, are several new experiments marked with an L, which 

 it is said were communicated from his own trials, by Mr. Charles Labelye, engi- 

 neer, and which concern particularly the weights of several sorts of stone and 

 other materials used in building. These Dr. D. has also distinguished by an L, 

 as they stand in Mr. Dodson's book. 



Mr. Geo. Graham, f.r.s. made for Dr. D. at the request of a friend, some 

 accurate trials on the weight, of gold and silver, both when reported fine, and 

 when reduced to the English standard; all which he has inserted under his name 

 in the following tables. Where he has also reported some other single experi- 

 ments which he occasionally met with, from Frederic Slare, m.d. John Keill of 

 Oxford, M.D. Stephen Hales, d.d. and Edward Bayley of Havant in Hamp- 

 shire, M.D. 



