TINNING, PLATING, &C. 321 



ject ; T am not yet quite satisfied ; though I take the liberty to say, 

 in opposition to Muratori, and the other respectable authorities 

 which I have quoted, that the applying a metallic covering to look, 

 ing. glasses is not a modern invention ; it is probable it was known 

 in the first century, if not sooner; and it is certain, I apprehend, 

 that it was known in the second. 



The Romans, before the time of the younger Pliny, not only 

 used <;lass, instead of gold and silver, for drinking vessels, but 

 they knew how to glaze their windows with it, and they fixed it in 

 the walls of their rooms to render their apartments more pleasant. 

 Now a piece of flat glass, fixed in the side of a room, is a sort of 

 looking-glass, and if the stucco into which it is fixed be of a dark 

 colour, it will not be a very bad one. And hence I think the 

 Romans could not fail of having a sort of glass specula in use : 

 but this, though admitted, does not come up to the point ; the 

 questidh is, whether they covered the posterior surface of the glass 

 with a metallic plate? It has been observed before, that the Ro- 

 mans knew how to make a paste of gold and quicksilver ; and it 

 appears from Pliny also, that they knew how to beat gold into thiu 

 leaves, and to apply it in that state both on wood and metal : now 

 there is a passage in Pliny, from whence it may be collected, that 

 the Romans began in his time to apply a coat of metal to glass 

 specula, and that this coat was of gold. The passage occurs in 

 the very place where Pliny professes to finish all he had to observe 

 concerning specula*. An opinion, says he, has lately been enter- 

 tained, that the application of gold to the back part of a speculum, 

 renders the image better defined. It is hardly possible that any 

 one should be of opinion, that a plate of gold put behind a metallic 

 speculum, could have any effect in improving the reflected image; 

 but supposing Pliny (whose transitions in writing are often abrupt) 

 to have passed from the mention of metallic to that of glass specula, 

 then the propriety of the observation relative to tbe improved state 

 of the image is very obvious. If we suppose the Romans, in 

 Pliny's age, to have simply applied some black substance to the 

 back surface of the glass, or even to have known huw to put tin 

 behind it, yet the observation of the image being rendered more 



* Atque ut omnia do -pe-culis prra^ inlur hoc loco Optima upud majorei 

 fuerant BrunJn^na stanno ct acre mixta. PraelaU sum argcntca. Primus 

 fecit Praxiteles, niagni Pompeii state. Nuper credi coeptum certiorem ima- 

 gine-in reddi auro apposito avenU. .Hist. Nat. 1. xuiii. *. ilv. 



Y2 



