The Collaborative International Dictionary of English v.0.48:

Stauroscope \Stau"ro*scope\ (st[add]"r[-o]*sk[=o]p), n. [Gr.
   stayro`s a cross + -scope.] (Crystallog.)
   An optical instrument used in determining the position of the
   planes of light-vibration in sections of crystals.
   [1913 Webster]