xe Historical Sketch of the Physical Sciences, 1818. 
B, Exhibiting only a tendency to the Metallic Lustre, which they 
acquire sensibly when polished. : 
Peroxide of iron, — Yenite, 
Black oxide of cobalt, Oxide of tantalum, 
Protoxide of uranium, Yttro-tantalite, 
Wolfram, . Black oxidized cerium. 
CLASS IV. 
Substances having a colour, depending on their nature, sus- 
ceptible of transparency m their perfect state. The property of 
insulating is limited to those varieties which approach that 
state. 
ORDER I. 
Susceptible of giving by reflexion the metallic lustre, and by 
reflection and refraction at once a colour more or less lively. The 
difference depends-on the polish of the surface. They all ac- 
quire resinous electricity by friction. 
Colour red by Transmission. 
Sulphuretted antimonioussilyer,  Oligiste iron ore, 
Sulphuret of mercury, Sulphuret of arsenic, 
Protoxide of copper, Oxide of titanium, 
Colour blue by Transmission. 
Titane anatase. 
ORDER Il. 
Destitute of the Metallic Lustre. Almost all acquire Resinous 
Electricity when rubbed. 
Moriate of mercury, Hydrate of copper, 
Chromate of lead, Sulphate of copper, 
Phosphate of lead, Phosphate of iron, 
Molybdate of lead, Arseniate of iron, 
Green carbonate of copper, Sulphate of iron, 
Blue carbonate of copper, Sulphuret of zinc, 
Arseniate of copper, Arseniate of cobalt, 
Dioptase copper, Oxide of uranium. 
Phosphate of copper, 
—— 
Il. GEOGNOSY. 
This: historical’ sketch has been insensibly carried to such a 
length, that lam deprived of the power of entering. into those 
geological details. which the popularity of the science, and the 
zeal with which it has been cultivated in Great Britain, and in 
some other countries, would have rendered both amusing and 
mstructive. I regret this preclusion the less, because the most 
