102 Dr. Falconer on the Knowledge 



" Between Ace, (or Ptolemais) and Tyre, the 

 ihore abounds with fmall eminences, which are 

 compofed of a vitrifiable earth. They fay, how- 

 ever, that it is not melted there, but brought to 

 Sidon to undergo that operation. Some fay, that 

 the Sidonians have a vitrifiable fand fit for fu- 

 fionj others fay the fand which is commonly found, 

 is ufed for that purpofe. I, myfelf, have heard 

 (fays Strabo) from the manufacturers of glafs at 

 Alexandria, that there is a certain vitrifiable 

 earth in Egypt, without which, the mod magni- 

 ficent, and varioufly coloured pieces of manufac- 

 ture cannot be made, as the diffei-ent kinds of glafs 

 require difi^erent mixtures of ingredients. Many 

 difcoveries alfo were made at Rome, both with 

 regard to the. beauty of the colour, and alfo as to 

 the facility of execution, efpecially in thofe kinds 

 of glafs that are made to refcmble chryftal." 



Seneca* was not only well acquainted with 

 »lafs as a fubftance, but alfo underftood its mag- 

 nifying powers when formed into a convex fliape. 



A glafs globe, fays he, filled with 

 A. D. 65. Yvater, makes letters viewed through 

 Mors. It, appear larger and brighter. The 



magnifying power of glafs confider- 

 ed as a more denfc, and of courfe a more 

 refrangible medium than air, was not unknown 



* 



Literse quamvis minutas & obfcurae per vitream pilam 

 ^c^ua plenam majores clarlorefque cernuntur, 



Senec. Quxft. Natur. I. 6. 



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