Why did Benjamin Franklin invent bifocals?

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Benjamin Franklin (1706-1790), one of the Founding Fathers as well as an author, printer, and scientist, invented bifocals because he suffered from presbyopia, a condition that means "age of sight" and that makes it harder for the eye to adjust to seeing objects at different distances as one ages. He had suffered from vision problems for a long time, probably dating back to the 1730s, and a print from 1764 shows Franklin wearing an usual pair of glasses that are likely bifocals. While Franklin was in Paris serving as the American envoy to the court of Louis XVI, Franklin wrote a letter dated August 21, 1784 to his friend George Whatley that read, "I cannot distinguish a letter even of large print; but am happy in the invention of double spectacles, which serving for distant objects as well as near ones, make my eyes as useful to me as ever they were.” This letter suggests that Franklin had already invented bifocals.

Bifocals have an upper part (which is less convex) that allows people to see objects at a distance and a lower part (which is more convex) that allows people to read. During Franklin's time, it was difficult for glassmakers to cut two separate lenses to make bifocals and to fuse them together in the same frame. Franklin also made several discoveries related to electricity. 

 

 

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