One of the most versatile and gifted people in American history announced the invention of bifocal eyeglasses this month in 1785. Benjamin Franklin had been using one pair of glasses to read with and another for distant vision. Tired of switching between pairs, he had the two pairs of lenses cut in half and mounted in the same frame. The idea of these split lenses, or bifocals, was slow to be adopted because of cost. Among Franklin’s many other inventions were watertight bulkheads for ships, the lightning rod, and the wood stove. Today, Americans spend over $8 billion a year at the nation’s 13,000 optical stores for frames and lenses, including bifocals. You can find current data on the country’s economy by downloading the America’s Economy mobile application at <www.census.gov/mobile>.