In physics, and electronics, the henry (symbol H) is the SI unit of inductance. It is named after Joseph Henry (1797–1878), the American scientist who discovered electromagnetic induction. (In England, Michael Faraday (1791–1867) discovered the same thing independently. They discovered it at about the same time.) The magnetic permeability of a complete vacuum is 4�×10−7 H/m (henry per meter).