Gold metal spectacles with one-piece (A segment) bifocal lenses
 Catalogue Number: 1747 Gold metal spectacles with one-piece (A segment) bifocal lenses Category: Spectacles and lenses Sub-Category: Spectacles (with lenses) Year Of Publication/Manufacture: c 1930 Time Period: 1900 to 1939 Description Of Item: Gold metal round eye spectacle frame 110 x 40 mm with saddle bridge and curl sides. The lenses are one-piece (A seg) bifocals with base-in prism ground only on the near segment. Historical Significance: Benjamin Franklin is generally credited with the invention of bifocals in 1784. These were two separate half lenses fitted together in the spectacle frame. They remained in use for over 100 years. Cemented bifocals were invented in 1884 and fused bifocals were invented in 1890. They had a lens segment of higher refractive index inserted in a concavity ground in the main lens and fused in place. One piece bifocals were invented in 1906. These were a single lens but with two different surface curvatures so there was an edge between the distance and near part of the lens. How Acquired: Donated by International Optical Co Date Acquired: May 1972 Condition: Good Location: Archive Office. Spectacles cabinet Drawer 12 |