periscope

periscope (pĕr`ĭskōp) [Gr.,=view around], instrument to enable a person to see objects not in his direct line of vision or concealed by some intervening body. Its essential parts are a tube, prisms, lenses, mirrors, and an eyepiece. The image is received in one mirror and reflected through the tube with its lenses to a mirror visible to the viewer. Periscopes used in submarines are so arranged that they can be turned to permit a view of the entire horizon, with built-in rangefinders and typically six times magnification. Submarine periscopes are of noncorrosive metal, have tubes up to 30 ft (9.1 m) long and about 6 in. (15 cm) in diameter (only a small section projects above the water), and may be withdrawn into the submarine. Many smaller types of periscopes are used in trenches and tanks. With the development of fiber optics, periscopes (known as cystoscopes or endoscopes) have become useful in medicine.

---

periscope

Optical instrument (see optics) used in land and sea warfare, submarine navigation, and elsewhere to enable an observer to see the surroundings while remaining under cover, behind armour, or submerged. A periscope includes two mirrors or reflecting prisms to change the direction of the light coming from the scene observed: the first deflects it down through a vertical tube, the second diverts it horizontally so that the scene can be viewed conveniently.