Hydroscope

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

One kind is an instrument for seeing 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. Despite common belief Hypatia did not invent the hydroscope, although others believe that Hypatia did help other inventors to build the instrument.