u SYSTEM OF 
vitriol is rjsquired, inftead of any other liquid^ to 
be mixed with the diamond powder. 
If the petty princes in thofe parts of the 
Indies where precious Hones are found 5 have 
no other power nor riches proportionable to 
the value of thefe gems ; the reafon of it is as 
obvious as of the general weaknels of thofe 
countries where gold and filver abound, viz. be- 
caufe the inhabitants, placing a falfe confidence 
in the high value of their poffeffions, negled: 
ufeful manufa6tures and trades, which by degrees 
produces a general idlenefs and ignorance thro’ 
the whole country. 
On the other hand, perhaps fome countries 
might fafely improve their revenues by fucli 
traffic. In Saxony, for example, there might 
probably be other, gems found, befides aqua- 
marines and topazes •, or even a greater trade 
carried on with thefe than at prefent, without 
danger of bad confequences ; efpecially under 
the diredtion of a careful and prudent govern- 
ment. 
The half precious Hones, fo called, or gems of 
lefs value, as the opal, the onyx, the chalcedony, 
the carnelian, and the coloured and uncoloured 
rock criHals, have been employed for ornaments 
and oeconomical utenfils, in which the price of 
the workmanfhip greatly exceeds the intrinfic 
value of the Hones. The antients ufed to en- 
grave concave or convex figures on them, which 
now-a-days are very highly valued, but often 
with lefs reafon than modern performances of 
the fame kind. Thefe Hones are worked by 
means of emery on plates of lead, copper, and tin, 
or with other ifiHruments ; but the common work 
on agates is performed at OberHein, with grind- 
Hones, at a very cheap rate. When once fuch a 
manufac- 
