Note 135 — Chapter VIII
Reading edition
Cornelius Agrippa is said to have possessed such a mirror. The Chinese make mirrors which, when placed in a particular light, show upon their polished faces the pattern on the back of the metal, although it is invisible in every other position. This is effected by giving different degrees of hardness to the various parts of the metal. In Natural Magic, by Sir David Brewster, several curious experiments belonging to this class are named.