Source : Webster's Revised Unabridged Dictionary (1913)

Nephoscope \Neph"o*scope\, n. [Gr. ? a cloud + -scope.]
   (Meteorol.)
   An instrument for observing the clouds and their velocity.

Source : WordNet®

nephoscope
     n : a grid-like measuring instrument for measuring the altitude,
         direction, and velocity of movement of clouds