What instrument did Benjamin Franklin invent to protect buildings from lightning?

Benjamin Franklin invented the lightning rod to protect buildings from lightning.

A lightning rod is a conductive metal rod or system connected to the ground by conductors. It provides a preferred path for a lightning discharge, directing the enormous electrical current safely toward Earth rather than through vulnerable building materials.

Franklin proposed the idea in the 1750s after arguing that lightning was an electrical phenomenon. His experiments and writings encouraged the installation of pointed metal rods on buildings. The device became widely known as a lightning conductor in Britain and as a lightning rod in the United States.

A lightning rod does not prevent lightning from forming or guarantee that a nearby strike will never occur. Effective protection also requires suitable grounding and bonding. Modern systems may use multiple air terminals and down conductors to control current paths.