Periscope
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Image:Fr scope.jpg Image:Periscope.png A periscope is an instrument for observation from a concealed position. In its simplest form it is a tube in each end of which are mirrors set parallel to each other and at an angle of 45° with respect to the line between them. It may be used as a toy or for seeing over people's heads in a crowd. This form of periscope, with the addition of a simple lens, was used for observation purposes in the trenches during World War I. More complex periscopes, using prisms instead of mirrors, and providing magnification, are used on submarines.
Early examples
Image:Submarine periscope.jpg Johann Gutenberg, better known for his contribution to printing technology, marketed a periscope in the 1430s to enable pilgrims to see over the heads of the crowd at the vigintennial religious festival at Aachen. Simon Lake used periscopes in his submarines in 1902. Sir Howard Grubb perfected it in World War I[1]. Morgan Robertson claims to have described a submarine using a periscope in his fictional works.
Periscopes, in some cases fixed to rifles, were used in World War I to enable soldiers to see out of the trenches.
Image:Gundlach periscope.jpg Periscopes were also extensively used in tanks, enabling drivers or tank's commanders to inspect the situation without leaving the safety of the tank. An important development was Gundlach's periscope allowing tank commander to obtain 360 degree view without moving the seats (pictured). The design was first used in the Polish 7-TP light tank. Shortly before the war it was given to the British and was used in most tanks of WWII, including the British Crusader, Churchill, Valentine, and Cromwell and the American Sherman. The design was later copied and used extensively in tanks of the USSR (including the T-34 and T-70) and Germany.
Naval use
Image:Warsaw Uprising observation.JPG A simple, fixed naval periscope using plane mirrors was built by the Frenchman Marie Davey in 1854. Thomas H. Doughty of the US Navy later invented a prismatic version for use in the American Civil War (circa 1891).
The invention of the collapsible periscope for use in submarine warfare is usually credited to Simon Lake in 1902, who called his device the omniscope or skalomniscope. There is also a report that an Italian, Triulzi, demonstrated such a device in 1901 calling it a cleptoscope.
Another early example of naval use of the periscope are the two adapted on the experimental French submarine Gymnote by the Captain Arthur Krebs in 1888 and 1889 (see in French : rbmn).
A modern submarine periscope incorporates lenses for magnification and functions as a telescope. It typically employs prisms and total internal reflection instead of mirrors, because prisms, which do not require coatings on the reflecting surface, are much more rugged than mirrors. It may have additional optical capabilities such as range finding and targeting. The mechanical systems of submarine periscopes are typically hydraulically powered and need to be quite sturdy to withstand the drag through water. The periscope chassis may also be used as to support a radio or radar antenna.
Submarines traditionally had two periscopes: a navigation periscope and a targeting, or commander's, periscope. These were originally mounted one forward of the other in the narrow hulls of diesel-electric submarines. In the much wider hulls of recent US Navy submarines, they are located side-by-side.
However, the most modern submarines no longer use periscopes. The United States Navy's Virginia-class submarines instead use photonics masts, which lift an electronic imaging sensor set above the water. Signals from the sensor set are transmitted electronically to workstations in the submarine's control center. While the cables carrying the signal must penetrate the submarine's hull, that hull opening is much smaller and more easily sealed — therefore less expensive and safer — than those required by periscopes.
See also
es:Periscopio eo:Periskopo (optika aparato) fr:Périscope he:פריסקופ nl:Periscoop ja:潜望鏡 no:Periskop pl:Peryskop (przyrząd optyczny) ru:Перископ (оптический прибор) tr:Periskop