The lightning rod was invented by Benjamin Franklin (1706–1790) around 1750 following his experiment with the kite and the key. In 1752, Franklin tied a metal key to the end of kite string and flew it during a thunderstorm. Franklin suspected that lightning was a natural form of electricity. He knew that if lightning was electricity, it would be attracted to the metal key. When sparks jumped from the metal key, he understood that electrical current had traveled from the electrified air above down the kite string to the key. This experiment confirmed that lightning is an electrical phenomenon. A lightning rod is often placed on the top of buildings to attract lightning bolts. They are designed to provide a safe path to ground the electricity so that it does not damage the building. In recent years, lightning rods have become even more important because the metal pipes that used to be installed for indoor plumbing and could serve as lightning rods are being replaced by nonconductive PVC pipes.