Ben Franklin invented the Bifocals. Franklin was both near sighted and far-sighted and became tired of switching between 2 sets of classes, so he invented the bifocals to see both near and far.
Ben Franklin's love of music prompted the invention of the Glass Armonica.
Yes, at the age of 8, Ben Franklin taught himself how to swim, just by reading a book. His love of swimming prompted him to create swimming fins. He often taught his friends how to swim. At one time he considered opening up a swim school.
http://www.childrenslit.com/childrenslit/mai_vanvleet_carmella_facts.html
http://www.biography.com/people/benjamin-franklin-9301234?page=3