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CHAP. 45. (9.)—MIRRORS.

It is generally supposed among us that it is only the very finest silver that admits of being laminated, and so converted into mirrors. Pure silver was formerly used for the purpose, but, at the present day, this too has been corrupted by the devices of fraud. But, really, it is a very marvellous property that this metal has, of reflecting objects; a property which, it is generally agreed, results from the repercussion of the air,1 thrown back as it is from the metal upon the eyes. The same too is the action that takes place when we use a mirror. If, again, a thick plate of this metal is highly polished, and is rendered slightly concave,2 the image or object reflected is enlarged to an immense extent; so vast is the difference between a surface receiving,3 and throwing back the air. Even more than this-drinking-cups are now made in such a manner, as to be filled inside with numerous4 concave facets, like so many mirrors; so that if but one person looks into the interior, he sees reflected a whole multitude of persons.

Mirrors, too, have been invented to reflect monstrous5 forms; those, for instance, which have been consecrated in the Temple at Smyrna. This, however, all results from the configuration given to the metal; and it makes all the difference whether the surface has a concave form like the section of a drinking cup, or whether it is [convex] like a Thracian6 buckler; whether it is depressed in the middle or elevated; whether the surface has a direction7 transversely or obliquely; or whether it runs horizontally or vertically; the peculiar configuration of the surface which receives the shadows, causing them to undergo corresponding distortions: for, in fact, the image is nothing else but the shadow of the object collected upon the bright surface of the metal.

However, to finish our description of mirrors on the present8 occasion—the best, in the times of our ancestors, were those of Brundisium,9 composed of a mixture of10 stannum and copper: at a later period, however, those made of silver were preferred, Pasiteles11 being the first who made them, in the time12 of Pompeius Magnus. More recently,13 a notion has arisen that the object is reflected with greater distinctness, by the application to the back of the mirror of a layer of gold.14

1 A very far-fetched explanation, and very wide of the mark.

2 "Paulum propulsa."

3 Which he supposes a concave surface to do.

4 This passage is noticed by Beckmann, in his account of Mirrors; Vol. II. p. 58. Bohn's Edition.

5 Distorting the image reflected, by reason of the irregularities of the surface. See Seneca, Nat. Quæst. B. i. c. 5.

6 "Parma Thræcidica."

7 He probably means, whether the surface is made convex or concave at these different angles.

8 A subject to which he returns iu various parts of B. xxxvi.

9 See B. xxxiv. c. 48.

10 As to the identification of "stannum," on which there have been great differences of opinion, see B. xxxiv cc. 47, 48, and the Notes.

11 For some account of this artist, see Chapter 55 and the Notes at the end of this Book.

12 "Silver mirrors were known long before this period, as is proved by a passage in the Mostellaria of Plautus, A. 1, S. 3. 1. 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.

13 "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.

14 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.

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