The Natural History of Pliny, Volume 6 (of 6) by the Elder Pliny

[1036] In Chapter 32. He alludes to the use of glair of eggs. [1037] Literally “whetstone.” He is speaking of the stone known to us as Touchstone, Lydian stone, or Basanite—“a velvet-black siliceous stone or flinty jasper, used on account of its hardness and black colour for trying the purity of the precious metals. The colour left on the stone after rubbing the metal across it, indicates to the experienced eye the amount of the alloy.”—Dana, Syst. Mineral., p. 242. [1038] In Lydia. See B. v. cc. 30, 31. [1039] As a test. At the present day, concentrated nitric acid is dropped on the mark left by the metal; and the more readily the mark is effaced, the less pure is the metal. [1040] This seems to be the meaning of “si sudet protinus.” [1041] A very far-fetched explanation, and very wide of the mark. [1042] “Paulum propulsa.” [1043] Which he supposes a concave surface to do. [1044] This passage is noticed by Beckmann, in his account of Mirrors; Vol. II. p. 58. _Bohn’s Edition._ [1045] Distorting the image reflected, by reason of the irregularities of the surface. See Seneca, Nat. Quæst. B. i. c. 5. [1046] “Parma Thræcidica.” [1047] He probably means, whether the surface is made convex or concave at these different angles. [1048] A subject to which he returns in various parts of B. xxxvi. [1049] See B. xxxiv. c. 48. [1050] As to the identification of “stannum,” on which there have been great differences of opinion, see B. xxxiv. cc. 47, 48, and the Notes. [1051] For some account of this artist, see Chapter 55 and the Notes at the end of this Book. [1052] “Silver mirrors were known long before this period, as is proved by a passage in the Mostellaria of Plautus, A. 1, S. 3, l. 101, where they are distinctly mentioned. To reconcile this contradiction, Meursius remarks that Pliny speaks only of his countrymen, and not of the Greeks, who had such articles much earlier, though the scene in Plautus is at Athens.”—Beckmann, Hist. Inv. Vol. II. p. 62. _Bohn’s Edition._ [1053] “Nuper credi cœptum certiorem imaginem reddi auro opposito aversis.”—“Of what Pliny says here I can give no explanation. Hardouin (qy. if not Dalechamps?) is of opinion that mirrors, according to the newest invention, at that period were covered behind with a plate of gold, as our mirrors are with an amalgam. But as the ancient plates of silver were not transparent, how could the gold at the back of them produce any effect in regard to the image? May not the meaning be that a thin plate of gold was placed at some distance before the mirror, in order to throw more light upon its surface? Whatever may have been the case, Pliny himself seems not to have had much confidence in the invention.”—Beckmann, Hist. Inv. Vol. II. p. 62. [1054] 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