Note 2 — Chapter II
Reading edition
The manufacture of glass was known very early, but glass perfectly transparent and colourless was reckoned so valuable, that Nero is said to have given a sum equal to £25 for two moderate sized colourless drinking glasses.—Starke’s Oriental Letters.
Glass for optical uses is heavy, homogeneous, free from streaks and veins. More expensive chemical substances are employed in its manufacture than are used in making common glass.