[Sca-cooks] Farsighted lenses

[Susan Lord Williams]

I wrote:

> I have never documented my findings on magnifying glasses for the farsighted but my gut feeling from my investigations during the 15th century is that they were available. I think they were available from the times of la Celestina and have asked my colleagues what info they might have. Actually it is perfectly logical that lenses were available from the 8th century in Cordoba when the crystal factory was founded to provide crystal wine glasses to the court thanks to Ziryab's contributions to refined living in Andalusia.
> 
> 
David Friedman replied:
> 
> Crystal as in glass or crystal as in clear quartz?
> 

http://en.wikipedia.org/wiki/Magnifying_glass states that “a magnifying devise” existed  in 424 BC. It does not specify whether it was glass, crystal or clear quartz. What is the difference? - It continues to state that “glass lenses” were produced in the Middle Ages. I assume that magnifying lenses were available.

Medieval Muslims, including those in Bagdad and Andalusia, worked with quartz and also they had a oops - glass or crystal factory (now that you question it I don’t know which) outside of Cordoba by the 9th century as Ziryab insisted that wine be drunk from glass  or crystal goblets. I don’t know enough about it to be able to say if they produced glass or crystal. 

Do we have an optometrist amongst us who knows about the history of the development of lenses?