url: http://inventors.about.com/library/inventors/blfranklin_inventions.htm
The bifocals are a miracle for those who are nearsighted and farsighted. Due to annoyance with having to switch glasses constantly, Benjamin Franklin created the bifocal, which has two lens in one pair of glasses (the distance lens at the top and the up-close lens at the bottom). This invention helped readers to a great extent because they were always wearing their reading glasses if they owned bifocals. It must have ben very beneficial for reading menus or enjoying a novel in the horse-drawn carriage.