Note 1054 — BOOK XXXIII. THE NATURAL HISTORY OF METALS.647 (continued 2)

Dr. Watson (Chemical Essays, Vol. IV. p. 246) seems to think that Pliny is here speaking of glass mirrors: “If we admit that Pliny was acquainted with glass mirrors, we may thus understand what he says respecting an invention which was then new, of applying gold behind a mirror. Instead of an amalgam of tin, some one had proposed to cover the back of the mirror with an amalgam of gold, with which the ancients were certainly acquainted, and which they employed in gilding.” See Chapter 20 of the present Book. On the above passage by Dr. Watson, Beckmann has the following remarks: “This conjecture appears, at any rate, to be ingenious; but when I read the passage again, without prejudice, I can hardly believe that Pliny alludes to a plate of glass in a place where he speaks only of metallic mirrors; and the overlaying with amalgam requires too much art to allow me to ascribe it to such a period without sufficient proof. I consider it more probable, that some person had tried, by means of a polished plate of gold, to collect the rays of light, and to throw them either on the mirror or the object, in order to render the image brighter.”—Hist. Inv. Vol. II. p. 72.