This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Periscope simple.svg simple periscopes Einfaches Funktionsprinzip des Periskops mit Spiegeln oder Umlenkprismen und dem jeweils beobachtenden Auge Principle of the periscope The periscope on the left uses mirrors at locations labled whereas the right uses prisms at locations The observer is Principio del periscopio Quello sinistra