One of the most famous achievements of Benjamin Franklin is the invention of the lightning rod. Franklin conducted his kite experiment to demonstrate the electrical nature of lightning during a thunderstorm. He flew a kite with a metal key attached to the string. When lightning struck the key, it electrified the string, which in turn shocked Franklin and caused him to drop the kite. This experiment provided strong evidence that lightning was a form of electricity. Franklin went on to develop the lightning rod, which is a metal rod that is installed on top of buildings and other structures to conduct lightning strikes safely into the ground.