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. 

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.

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.