The Inventions of Benjamin Franklin
•Bifocals: Franklin was both nearsighted and farsighted, and had to alternate between two pairs of glasses depending on what he was trying to see. As a solution to his frustrating problem, Franklin had the lenses from his two pairs of glasses cut in half and reassembled in one frame with the lenses for distance on top and the lenses for reading on the bottom. Franklin's idea for bifocals is still the basic model used today.
•Franklin stove: Most homes in colonial America were heated by fires in open fireplaces. Fireplaces were inefficient heat sources because of the large amount of wood needed and were dangerous because sparks could easily ignite a fire elsewhere in the house. Franklin invented an iron furnace stove that used less wood, radiated more warmth through the heated iron, and was safer because the fire was better contained. Franklin stoves are still in use in some homes today.
•Glass Harmonica: While Franklin was traveling in Europe, he witnessed an amateur musician play on a set of "singing glasses," producing clear, ringing sounds by rubbing a moistened finger on the rims of wine glasses filled with varying levels of water. Intrigued, Franklin worked to create an instrument that incorporated the elements of the singing glasses. He selected different-sized wine glasses, removed the stems, drilled holes in the bottoms of the glasses, and corked the holes. The glasses were arranged in order of increasing size on a horizontal spindle, which could be rotated by a foot treadle. Musicians played the glass harmonica by touching moistened fingers to the edges of the glasses while rotating them with the pedal. The glass harmonica fell out of favor in the mid-nineteenth century, but is currently making a comeback because of the efforts of a German glassblower.
•Lightning Rod: Franklin's investigations into the nature of electricity led him to this simple invention with a powerful purpose. By mounting a pointed iron rod on the highest point of a building, Franklin discovered that it would attract lightning flashes and channel the electrical current to the ground, thereby preventing other parts of the building from catching on fire. Lightning rods can be found on buildings today, although they are usually made of copper.
•Odometer: While serving as postmaster for the northern colonies, Franklin had to establish mail routes. In order to measure distances, he invented an odometer, which could be attached to the axle of his carriage wheels to count the rotations. Odometers are standard instruments in modern vehicles.