Who invented bifocals?

Benjamin Franklin invented bifocals. In a letter to his friend George Whatley in 1784, Franklin dubbed the bifocals "double spectacles." They are made by combining convex and concave lenses so that both nearsighted and farsighted vision can be corrected by the same glasses.

Franklin invented the lightning rod, a musical instrument called a glass armonica and the Franklin stove. His experimentation with electricity helped further the understanding of how electrical currents work. A Founding Father of the United States, he is the only person to have signed the Declaration of Independence, the Treaty of Alliance with France, The Treaty of Paris and the Constitution of the United States.