galvanometer
    n 1: meter for detecting or comparing or measuring small
         electric currents

Galvanometer \Gal`va*nom"e*ter\, n. [Galvanic + -meter: cf. F.
   galvanom[`e]tre.] (Elec.)
   An instrument or apparatus for measuring the intensity of an
   electric current, usually by the deflection of a magnetic
   needle.
   [1913 Webster]

   Differential galvanometer. See under Differental, a.

   Sine galvanometer, Cosine galvanometer, Tangent
   galvanometer (Elec.), a galvanometer in which the sine,
      cosine, or tangent respectively, of the angle through
      which the needle is deflected, is proportional to the
      strength of the current passed through the instrument.
      [1913 Webster]