Optical telegraph in the context of Telegraph code

Optical telegraph in the context of Telegraph code

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⭐ Core Definition: Optical telegraph

An optical telegraph is a line of stations, typically towers, for the purpose of conveying textual information by means of visual signals (a form of optical communication). There are two main types of such systems: the semaphore telegraph which uses pivoted indicator arms and conveys information according to the direction the indicators point, and the shutter telegraph which uses panels that can be rotated to block or pass the light from the sky behind to convey information.

The most widely used system was the Chappe telegraph, which was invented in France in 1792 by Claude Chappe. It was popular in the late eighteenth to early nineteenth centuries. Chappe used the term télégraphe to describe the mechanism he had invented – that is the origin of the English word "telegraph". Lines of relay towers with a semaphore rig at the top were built within line of sight of each other, at separations of 5–20 miles (8–32 km). Operators at each tower would watch the neighboring tower through a telescope, and when the semaphore arms began to move spelling out a message, they would pass the message on to the next tower.

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👉 Optical telegraph in the context of Telegraph code

A telegraph code is one of the character encodings used to transmit information by telegraphy. Morse code is the best-known such code. Telegraphy usually refers to the electrical telegraph, but telegraph systems using the optical telegraph were in use before that. A code consists of a number of code points, each corresponding to a letter of the alphabet, a numeral, or some other character. In codes intended for machines rather than humans, code points for control characters, such as carriage return, are required to control the operation of the mechanism. Each code point is made up of a number of elements arranged in a unique way for that character. There are usually two types of element (a binary code), but more element types were employed in some codes not intended for machines. For instance, American Morse code had about five elements, rather than the two (dot and dash) of International Morse Code.

Codes meant for human interpretation were designed so that the characters that occurred most often had the fewest elements in the corresponding code point. For instance, Morse code for E, the most common letter in English, is a single dot ( ▄ ), whereas Q is  ▄▄▄ ▄▄▄ ▄ ▄▄▄ . These arrangements meant the message could be sent more quickly and it would take longer for the operator to become fatigued. Telegraphs were always operated by humans until late in the 19th century. When automated telegraph messages came in, codes with variable-length code points were inconvenient for machine design of the period. Instead, codes with a fixed length were used. The first of these was the Baudot code, a five-bit code. Baudot has only enough code points to print in upper case. Later codes had more bits (ASCII has seven) so that both upper and lower case could be printed. Beyond the telegraph age, modern computers require a very large number of code points (Unicode has 21 bits) so that multiple languages and alphabets (character sets) can be handled without having to change the character encoding. Modern computers can easily handle variable-length codes such as UTF-8 and UTF-16 which have now become ubiquitous.

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Optical telegraph in the context of Telegraph

Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas pigeon post is not. Ancient signalling systems, although sometimes quite extensive and sophisticated as in China, were generally not capable of transmitting arbitrary text messages. Possible messages were fixed and predetermined, so such systems are thus not true telegraphs.

The earliest true telegraph put into widespread use was the Chappe telegraph, an optical telegraph invented by Claude Chappe in the late 18th century. The system was used extensively in France, and European nations occupied by France, during the Napoleonic era. The electric telegraph started to replace the optical telegraph in the mid-19th century. It was first taken up in Britain in the form of the Cooke and Wheatstone telegraph, initially used mostly as an aid to railway signalling. This was quickly followed by a different system developed in the United States by Samuel Morse. The electric telegraph was slower to develop in France due to the established optical telegraph system, but an electrical telegraph was put into use with a code compatible with the Chappe optical telegraph. The Morse system was adopted as the international standard in 1865, using a modified Morse code developed in Germany in 1848.

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Optical telegraph in the context of Semaphore

Semaphore (lit. 'apparatus for signalling'; from Ancient Greek σῆμα (sêma) 'mark, sign, token' and Greek -φόρος (-phóros) 'bearer, carrier') is the use of an apparatus to create a visual signal transmitted over distance. A semaphore can be performed with devices including: fire, lights, flags, sunlight, and moving arms. Semaphores can be used for telegraphy when arranged in visually connected networks, or for traffic signalling such as in railway systems, or traffic lights in cities.

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LINKED FROM (PARENTS)
← Telegraph ← Telegraphy ← Semaphore ← Telegraph office ← Telegram ← Telegraph code
LINKS TO (CHILDREN)
Claude Chappe → Nalbach → Optical communication → Chappe telegraph → Telegraph → Telescope →