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Unit 2: Those Inventive Americans!

Suggested Activities

Benjamin Franklin

Era 3: Revolution and the New Nation

  1. Benjamin Franklin's keen interest in improving the world around him and his natural curiosity for the way things worked are evident in his inventions. Franklin is credited with inventing bifocals, the Franklin stove, the glass harmonica, the lightning rod, and the odometer. Choose two of these inventions and write a brief report addressing the following: Why did Franklin invent it? How did it work? Is it still in use today? Illustrations of these inventions can be seen at the Franklin Institute Science Museum Web site (
    [Standard 4—historical research capabilities]

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.

Benjamin Franklin (1706–1790)
Joseph Siffred Duplessis (1725–1802)
Oil on canvas, 1785
Gift of the Morris and Gwendolyn Cafritz Foundation

  1. Electricity was a topic of much fascination for Franklin, and he set about to study electrical phenomena in earnest in the mid-1740s. Most people have heard about Franklin's experiment with the kite and the key. Explain what he was trying to prove with this demonstration. Was it successful?
    [Standard 4—historical research capabilities]

Through earlier experiments and observations made by himself and others, Franklin had concluded that electricity was attracted to metal. In order to determine the nature of lightning, which Franklin suspected was an electrical current, he had to see if lightning would pass through metal. Franklin constructed a kite with a sharp metal wire at the top (to attract the lightning) and a metal key tied to the bottom. While flying the kite in a thunderstorm, lightning struck the metal wire and traveled down the kite string to the key held by Franklin. Fortunately, Franklin was not injured by the electrical shock he received during this dangerous experiment, and the experiment was a success.

Classroom activities demonstrating the properties of electricity can be found at the Franklin Institute Science Museum Web site ( html#electric).
  1. Benjamin Franklin wrote a letter to an acquaintance in France in which he said that he would like to be embalmed and come back to see America in a hundred years. How do you think Franklin would have reacted to seeing America today, more than two hundred years after his death? Imagine you are Franklin and have been granted your wish to return to life for one day. Write an essay in Franklin's voice, commenting upon American life in the early twenty-first century.
    [Standard 3—historical analysis and interpretation]