no Dr. Falconer on the Knowledge 



handles to each, and of no extraordinary flzf, 

 fix thoufand feftertia, or nearly fifty thoufand 

 pounds fterling. But although the finer kinds 

 appear to have been fo rare and valuable, the in- 

 ferior kinds mull have been not unconnmon, fince 

 Pliny fays, that the ufe of glafs cups had nearly 

 fuperfeded thofe of gold and filver. — Pliny like- 

 wife knew the power of a hollow glafs globe, 

 filled with water, in concentrating the rays of 

 light, fo as to produce flame in any combuftible 

 fubftance upon which the focus fell ; and alfo 

 mentions, that fome furgeons in his time, made 

 ufe of it as a cauftic * for ulcers. He was like- 

 wife acquainted with the comparative hardnefsof 

 gems and glafs, as he obferves, that the lapis 

 obfidianus would not fcratch the true gems; and 

 -f he alfo mentions the counterfeiting of the latter 

 in his time, as a very lucrative art, and brought to 

 great perfedlion. The fame author mentions, 

 that glafs might be cut or engraven upon by 

 means of diamonds, which art is evidenced by 

 the antique gems fo frequently found. 



The ruins of the city of Pompeia, which was 



deflroyed in the time of Pliny, have 



' afforded examples of the ufe of glafs 



in windows. I was informed by a gentleman of 



accuracy, that he had meafured a pane of glafs 



* L. XXXVII. Cap. 2. 

 t L. XXXVII. Cap. 13. 



found 



