Source : Webster's Revised Unabridged Dictionary (1913)

Hydroscope \Hy"dro*scope\, n. [Hydro-, 1 + -scope.]
   1. An instrument designed to mark the presence of water,
      especially in air. --Weale.

   2. A kind of water clock, used anciently for measuring time,
      the water tricking from an orifice at the end of a
      graduated tube.