[Sca-cooks] Farsighted lenses

[Susan Lord Williams]

I like this article: http://www.antiquespectacles.com/history/ages/through_the_ages.htm

I think catches the bull by the horns:

"But it was definitely the city of Florence that by the middle of the fifteenth century led in innovation, production, sale, and spread of spectacles within and outside Italy as attested by documents already or soon to be published. In particular, Published evidence in the form of letters of the dukes of Milan, Francesco and Galeazzo Maria Sforza, dated 1462 and 1466 respectively, reveal the first detailed information about spectacles since their invention; namely, 1. Florence was producing in large quantities not only convex lenses for presbyopes, but also concave (diverging) lenses for myopes (i. e., about a half century before the latter were thought to have been developed); 2. Florence had become the leading manufacturer of readily available and affordable good-quality spectacles; 3. Florentine spectacle makers were well aware of the fact that visual acuity declines gradually after the age of thirty, and were constructing lenses progressively graded in five-year strengths for hyperopes or presbyopes and in two strengths for myopes, practically prescription lenses; 4. The dukes of Milan were ordering prestigious Florentine glasses by the hundreds to give them away as gifts to their courtiers, the first record of such a phenomenon in the literature. The massive documentation available only in Florence for this early period has revealed the name of fifty-two spectacle makers between 1413 and 1562 and the location of their shops. The large numbers of spectacles circulating in northwest Europe (especially London) from the 14th century were being mass produced in the Low Countries. They were then manufactured in England beginning in the 15th century. Other centers of production like Germany, France, and Netherlands began to appear more frequently in the sources only by the sixteenth century but they never produced anything near the quantity of the Florentine documentation until well into the seventeenth century. The documents from Florence and other places will be discussed along with archeological evidence recently discovered in various digs in Europe in the forthcoming book, "Renaissance Vision from Spectacles to Telescopes," by Vincent Ilardi". (Translations of the two key 1460's letters)

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> I wrote:
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>> 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.
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> David Friedman replied:
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>> Crystal as in glass or crystal as in clear quartz?
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