Henry (symbol H) is the SI derived unit of inductance. It is named after Joseph Henry (1797–1878), the American scientist who discovered electromagnetic induction independently of and at about the same time as Michael Faraday (1791–1867) in England. The magnetic permeability of the vacuum is 4π×10−7 H/m (henry per meter).
The National Institute of Standards and Technology provides guidance for American users of SI to write the plural as henries.
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