and its Utility in the Arts. 21 
In the Memoirs of the Swedifh Academy for 1751, there 
¥s an account of feveral experiments on platina, by Theodore 
- Scheffer; but the moft interefting of thefe is one which 
proves that this metal may be reduced to complete fufion 
when united with avery fmall quantity of arfenic. William 
Lewis, who made a valuable feries of experiments on the 
fame fubje&t, would not repeat the experiment of Scheffer, 
becaufe it appeared to him abfurd to reduce a refractory me- 
tal to a ftate of fufion, by means of a fubftance which a 
moderate heat fublimes and volatilifes. The alluftrious 
Turgot, whofe talents and virtues, fuperior to the age in 
which he lived, will be handed down to the remoteft pofte- 
rity, fent to Peru during his adminiftration the celebrated 
botanift Dombei. This voyage, the object of which com- 
prehended great and enlarged views, was of equal import- 
ance to the arts and the fciences; and Dombei,, according 
to the inftructions given him, was to {pare no pains to pro- 
cure for men of fcience fuch a quantity of platina as might 
be ufeful to them in their refearches. Turgot, whofe know- 
ledge in natural philofophy was profound and extenfive, had. 
forefeen that a metal indeftructible by its nature would be 
of ineftimable value in the conftruétion of telefcopes, and 
of thofe inftruments which navigators employ at fea to de- 
termine the longitude by the diftance of the fun and ftars 
from the moon. All opaque bodies are not equally pro- 
per for reflecting the light in a regular manner, and indeed 
thofe which poflefs this ufeful property are very few in num- 
ber. Tempered fteel, pyrites known under the name’ of 
the Inca’s {tone, and glafs covered at the back with tin, can~ 
not be employed in forming fpecula for telefcopes, though 
they reflect the light regularly. The violent friction necef- 
fary to polifh tempered fteel; the nature and imperfections 
of pyrites; the difficulty of avoiding double refraction in 
quickfilvered glafs, are the caufes which, prevent thefe fub- 
ftances from being ufed. Opticians, therefore, have hi- 
therto been obliged to employ for this purpofe a metal com- 
C3 pofed 
