How did Ben Franklin come to invent bifocal glasses?

Benjamin Franklin is both farsighted and nearsighted.

Before the invention of bifocal glasses, people with both conditions have to constantly switch two different glasses which might felt inconvenient.

So, Benjamin Franklin tried to do something to deal with this situation. He tried to make a horizontal cut through the lens of each glasses and combined them into one pair of glasses. This one new pair glasses is what eventually called as the bifocal glasses.

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