Hydroscope

• One kind is an instrument for making observations below the surface of water, such as a long tube fitted with various lenses arranged so that objects lying at the bottom can be reflected upon a screen on the deck of the ship that carries it. These are built with a large tire tube that supports the screen and covered by an acrylic dome for protection.
• Another kind detects subsurface water through nuclear magnetic resonance using the surface nuclear magnetic resonance technique.
• An instrument called hydroscope is described by Synesius in his Letter 15 to Hypatia