A periscope is an instrument for directing rays of light from one direction to another so that we can see things which, without it, would be obscured by some opaque object between us and them.

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Photo credit: © World History Archive / Alamy / Afripics
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Keywords: archival, archive, directing, historical, history, instrument, lens, light, military, mirror, naval, observation, optics, periscope, physics, rays, view