The Collaborative International Dictionary of English v.0.48:

Dynameter \Dy*nam"e*ter\, n. [Gr. ? power + -meter: cf. F.
   dynam[`e]tre. Cf. Dynamometer.]
   1. A dynamometer.
      [1913 Webster]

   2. (Opt.) An instrument for determining the magnifying power
      of telescopes, consisting usually of a doubleimage
      micrometer applied to the eye end of a telescope for
      measuring accurately the diameter of the image of the
      object glass there formed; which measurement, compared
      with the actual diameter of the glass, gives the
      magnifying power.
      [1913 Webster]