[ 453 ] • 
than as two and a half to one $ it may well be fufpefted, 
that the Granatc, Pfendo-Topazius, Sapphire, and 
fiich other Gemms which greatly exceed Chryftal 
in weight, do contain a confiderable portion of fome 
fort of Metal in their compofition: as was obferved 
of thefe bodies by Dr. Woodward, in his Method 
ofFoflils, p. 24, 
As to the white Sapphire, which is reputed by 
Dr. Woodward to be a fpecies of Gemm interme- 
diate between Chryftals and the Diamond in hard- 
nefs, I have not yet obtained any good account of 
its fpecifk gravity. 
The weight of the Diamond is ascertained in- 
N«. 476. of the Philofopkical Tranfadtions , where 
it appears, that by experiments made with the 
greateft care, by Mr. "John Ellico-t F. R. S. with 
moft exaft infiruments, and upon 14 different Dia- 
monds, fome of them very large, brought from 
different places, and having the greateft varieties of 
colour and fhape poffible ; they were all found to 
agree in weight to a furprifing degree of accuracy, 
being all Somewhat above three times and a half 
the weight of common water. 
This indeed differs very fenfibly from what had 
been found in fome former experiments, but it is 
hardly probable that thofe had been made upon 
Diamonds of fo large a fize as thefe: Mr. Boyle 
who found their weight lefs than 3 times that of 
common water, has himfelf told us in the fame 
place, V. 83 . h. that the done he made ufe of only 
weighed about 8 grains. And tho no doubt can be 
made of the exaftnefs of Sir Ifaac Newtons expe- 
riment,. 
