Design of a persicope. The model on the left uses mirrors, the one on the right uses prisms
A periscope is an optical instrument that is used to watch a scene from cover. The classical design uses a number of mirrors or prisms, and is used in tanks and submarines.
Images for kids
Australian Light Horse troops using a periscope rifle, Gallipoli, 1915. Photograph by Ernest Brooks.
An Auxiliary Periscope for Submarines from The Electrical Experimenter, Vol. IV, No. 38., 1916