As Benjamin Franklin grew old, his vision, which had never been great, deteriorated even further. Franklin came up with the idean that would help him to see long distances and be able to read. He invented "double-spectacles" later to beome known as bifocals. In 1784, Franklin wrote to his optician and asked him to take his long distance glasses and his reading glasses, cut the lenses in half and then put lenses together with the reading glasses on the bottom and the long distance glasses on the top.
In 1741, Franklin began working on the design of a more efficient fireplace for colonial homes. Franklin's aim was to limit the amount of smoke that poured into the home, maximize the amount of heat captured from the fire and would reduce the amount of wood they would need to burn as well as reduce the frequency of house fires.
The Glass Armonica
Franklin attended a concert where a musician was playing on glasses filled with water and was intrigued by the beauty of the sound of made. He set to work on his own musical creation.
"Working with a glassblower in London, Franklin made a few dozen glass bowls, tuned to notes by their varying size and fitted one inside the next with cork. Each bowl was made with the correct size and thickness to give the desired pitch without being filled with any water. Franklin also painted them so that each bowl was color-coded to a different note. A hole was put through the center of the glass bowls, and an iron rod ran through the holes. The rod was attached to a wheel, which was turned by a foot pedal. Moistened fingers touched to the edge of the spinning glasses produced the musical sounds." (http://www.fi.edu/learn/sci-tech/armonica/armonica.php?cts=benfranklin-recreation)