I G On the Catoptrkal and Dioptrical 



of quicksilver in the constructing of .spea/Zdr, or looking- 

 glasses (which I presume is of no great antiquity), the re- 

 flection of im3<>-cs by such specula must have been efiected 

 by being besmeared behind, or tinged through, with some 

 dark colour, especially black, which would obstruct the 

 refraction xjf the rays of light." But I presume that those 

 who duly attend to Abat's quotations and reasonings, will 

 be of opinion that Mr. Nixon s language is abundantly too 

 strong, when he says that the antients )nust have so be- 

 i^nicared or tinged their looking-glasses; since ylhat has 

 clear-.- proved thai they knew how to coat them with metal. 

 Among otiier uses to which glass was applied by the an- 

 tients, Mr. Kixon quotes from Plinij these passages : — ■ 

 '■ Cnm cddiid aqua, vitrece piUe, sole adrerso, in tantum 

 vxcandescuii t , nt vestcs cvurani : ijiass globes, with the ad- 

 dition of wai.-r, when exposed to the sun, grow so hot as 

 to burn clothes;" //Y'. xxxvi. c. '2-2. § 45. (The reader will 

 observe Plini/'s mistake in saying that the gloljes grow- thus 

 iiot.) Again: ^' Lwenlo ■medico'i, qiue swit ureitda corpo-^ 

 Turny 71071 aliUr uti/ius idjieri pulare, quam cnjslal/ind pdd 

 cdreri^is posltd solis radtls : 1 -tind that medical men are of 

 opinion, that there is not 9. more useful way to cauterize 

 parts of the body, than by a crystal globe placed opposite to 

 iheraya of the sun ;■' lib. xxxvii. c. 6>§ 10. JVir. Aixo/iadds, 

 on the authority of M. Renaudot, iu Mem. de I' Acad, des 

 iiiscript. torn. \. that glass was not wrought into lenses for 

 optical uses, till the beginning of the thirteenth century; so 

 that we may add hi? suffrage to those of the other learned 

 fcxutors of Roger Bacon's pretensions. -He also endeavours 

 to make it probable, '•' that the original of glass windows 

 Hiay have fair pretensions to a place some \ cars before the 

 destruction of Herculaneum {anno Chrisii 80), in whose 

 ruins the glass plate under consideration was buried." But 

 be confesses, he *' has not been able to trace up the use of 

 glass in windows, by any positive authority, higher than 

 ibout 200 years short of the epocha last mentioned, viz. to 

 'he latter end of the third century, when it is expressly 

 uientioned by Lactaniiui [De Opifkio Dei, cap. v.) in these 

 >vords : " ManifestiiiS est mentc7)i esse, qua per ocuhs ea, 

 <f.U(^ suni oppoiiia, traiispleiat, quasi per fenestras, hicenie 

 vilro aat speculari lapide obductas : It is more manifest that 

 there is a mind, which sees things presented to it through 

 the eyes, as through windows composed of clear glass, or 

 ..:;i--parent stone." 



iC. On this subject, it may not be amiss to add, that 

 in the reip-nof Tilcriw;, according to PUmi. a Roman artist 

 V ) had 



