The Collaborative International Dictionary of English v.0.48:

Henry \Hen"ry\, n.; pl. Henrys. [From Joseph Henry, an
   American physicist.]
   The unit of electric induction; the induction in a circuit
   when the electro-motive force induced in this circuit is one
   volt, while the inducing current varies at the rate of one
   amp[`e]re a second.
   [1913 Webster]