126 plii^t's natukal history. [Book XXXIII. 



in contact with it, it should immediately be covered with 

 steam,^^ the cloudiness disappearing at once. 



CHAP. 45. (9.) MIEEOES. 



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 daj, 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,®^ 

 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,®" the image or object reflected is 

 enlarged to an immense extent ; so vast is the diflPerence be- 

 tween a surface receiving,®^ and throwing back the air. Even 

 more than this — drinking-cups are now made in such a 

 manner, as to be filled inside with numerous®^ 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 monstrous^^ 

 forms ; those, for instance, which have been consecrated in the 

 Temple at Smyrna. This, however, all results from the con- 

 figuration given to the metal ; and it makes all the diflPerence 

 whether the surface has a concave form like the section of a 

 drinking cup, or whether it is [convex] like a Thracian®* 

 buckler ; whether it is depressed in the middle or elevated ; 

 whether the surface has a dii-ection^^ transversely or ob- 

 liquely ; or whether it runs horizontally or vertically ; the 

 peculiar configuration of the surface which receives the shadows, 



"'^ This seems to be the meaning of "si sudet protinus." 



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



^° " Pauluni pvopulsa." 



^^ Which he supposes a concave surface to do. 



®2 This passage is noticed by Beckmana, in his account of Mirrors ; 

 Vol. II, p. 58. Bohn's JEdition. 



^2 Distorting the ima^e reflected, by reason of the irregularities of the 

 surface. See Seneca, Nat. Quaest, B. "i. c. 5. 



^[ " Parma Thraecidica." 



®^ He probably means, whether the surface is made convex or concave 

 at these different andes. 



