A periscope is a very useful and interesting optical instrument. It enables officers aboard a submerged submarine to observe whatever might be happening on the surface. A submarine’s periscope can move up and down and turn to look in a complete circle. It allows tank commanders to view the battlefield from inside their armoured vehicles. It is therefore, useful in land and sea warfare. Now let us see what exactly a periscope is.
A periscope is an optical instrument with which a person can see around corners and other obstructions. This instrument is based upon the principle of reflection of light from two parallel mirrors. A simple periscope consists of a long tube bent twice at right angles. Two plane mirrors, parallel to each other, are fixed in such a way, that the reflecting surfaces of the two mirrors make an angle of 45° with the axis of the tube. Rays coming from an object in front of the periscope, after undergoing two successive reflections, reach the eye of the observer thus enabling him to see the object.
Some sophisticated periscopes also make use of reflecting prisms and magnifying optics, which make distant objects, appear closer. They are also fitted with devices for estimating the range of the target. Objects can be photographed through a periscope.
Simple periscopes, made of cardboard, are also popular among spectators at parades and sporting events. With its help, they can see above people’s heads!
Periscopes are also used in industry to observe nuclear reactions and the interiors of special furnaces and other dangerous devices.
The longest periscope in the world measures 27 m. It is located at the National Reactor Testing in Idaho Falls, Idaho. It is used to view nuclear reactor operations.
