The word hydroscope is used to mean any of several instruments related to water.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
