| Lenses |
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| • | Lenses for
eyeglasses are first mass-produced in Venice in |
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| about 1275.
Porta gives the first description of the process in |
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| “Magiae
Naturalis” (1588), which differs little in principal from |
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| that generally
used up to 1915. |
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| • | Porta uses the
term pilae vitreae to designate the cylinders of |
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| glass from
which sections are sliced with a diamond cutter |
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| and are sent
from Germany to Venice for polishing. This is the |
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| term (hollow
balls, filled with water) used by to describe |
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| magnifiers in antiquity. |
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