Source : Webster's Revised Unabridged Dictionary (1913)

Spherometer \Sphe*rom"e*ter\, n. [Sphere + -meter: cf. F.
   sph['e]rom[`e]tre.] (Physics)
   An instrument for measuring the curvature of spherical
   surface, as of lenses for telescope, etc.

Source : WordNet®

spherometer
     n : a measuring instrument for measuring the curvature of a
         surface