Definitions for "Periscope"
an optical instrument of tubular shape containing an arrangement of lenses and mirrors (or prisms), allowing a person to observe a field of view otherwise obstructed, as beyond an obstructing object or (as in submarines) above the surface of the water.
Optical arrangement which feeds light (usually from the sky background) into the slit of a spectrograph. These can be used when the object being observed would otherwise fill the slit and so no sky signal would be recorded.
An optical instrument, housed in a long tube; used to translate the observer's line of sight in a vertical direction.
Keywords:  spying, sister, brother, great, big
a great tool for spying on your big brother or sister
a simple device for seeing around corners
A device with two mirrors to help you see around corners.
Tube used for looking from a submerged vessel to the surface.
Keywords:  comprehensive, view, general
A general or comprehensive view.