water telescope

from The Collaborative International Dictionary of English v.0.48

Water telescope \Water telescope\
   1. (Optics) A telescope in which the medium between the
      objective and the eye piece is water instead of air, used
      in some experiments in aberration.
      [Webster 1913 Suppl.]

   2. A telescope devised for looking into a body of water.
      [Webster 1913 Suppl.]