C 778 ) 
If. An Account of certain tranfparent Pebfefj 
rnofily of the P^ape of the Ombriae or Bron- 
tiae : Wherefore I have called them Brontiae 
Laeves, Pellucidae, Refplendentes, Adaman- 
tum JEmuls. 
TH E Figures are taken from certain very dfcar and 
tranfparent Stones found in England, of a con- 
ftant Shape. They are called in lome ancient Leafes of 
Royal Mines Rough or Mineral Pearl. They under- 
standing, as I guefs, by the Word Pearl, any thing that 
^vas relplendent and bright , and particularly figured 
like a Drop of Water, which thefe Stones have of them- 
felves naturally, and withQut any Artifice ; Tome of them 
x being exa&ly Spherical, others like a Half Globe, others 
like a Half Oval, with an edge raifed on the top : And 
in thefe general Figures great Varieties are to be ob- 
ferved. 
. As for the Efteem the Ancients had of them, it was 
not without Reafon ; for befides that, their natural Fr- 
gure and Beauty, where they have been well preferved, 
is commendable. Their Natural P6lifh is moreover not 
to be counterfeited, but very eafie to be diftinguilh'd by 
a "Microfcope, from the Artificial Polifh of Glafs and 
Cryftals. Now Gold, Silver, Diamonds and Pearl are 
for no other realbn eftimable, but becaufe they have 
certain indelible Charadters,which all the Subtilty and Wit 
of Man hath not yet been able to Counterfeit, nonvith- 
ftanding the many Pretences thereunto. As Gold, for 
Example, for that it will endure the drowning in Antimo- 
ny Silver, that it abides the Teft of Lead- Diamonds, 
for that of themfelves, even without a Foil, they caft a 
Luftre. 
