View source for Semaphore telegraph (nonfiction)

[[File:Signaling_by_Napoleonic_semaphore_line.jpg|thumb|Illustration of communication by mechanical semaphore in 1800s France.]]A '''semaphore telegraph''' is a system of conveying information by means of visual signals, using towers with pivoting shutters, also known as blades or paddles.

[[Information theory (nonfiction)|Information]] is encoded by the position of the mechanical elements; it is read when the shutter is in a fixed position.

The most widely used system was invented in 1792 in France by [[Claude Chappe (nonfiction)|Claude Chappe]], and was popular in the late eighteenth to early nineteenth century.

They were much faster than post riders for conveying a message over long distances, and also had cheaper long-term operating costs, once constructed.

Semaphore lines were a precursor of the electrical telegraph, which would replace them half a century later, and would also be cheaper, faster, and more private.

The distance that an optical telegraph can bridge is limited by geography and weather; thus, in practical use, most optical telegraphs used lines of relay stations to bridge longer distances. This also prevented the optical telegraph from crossing wide expanses of water, unless a convenient island could be used for a relay station. 

Modern derivatives of the semaphore system include flag semaphore (a flag relay system) and the heliograph (optical telegraphy using mirror-directed sunlight reflections).

== In the News ==

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== Fiction cross-reference ==

* [[Gnomon algorithm]]
* [[Gnomon Chronicles]]

== Nonfiction cross-reference ==

* [[Claude Chappe (nonfiction)]]
* [[Electrical telegraph (nonfiction)]]

External links:

* [https://en.wikipedia.org/wiki/Semaphore_line Semaphore line] @ Wikipedia
* [https://en.wikipedia.org/wiki/Prussian_semaphore_system Prussian semaphore system] @ Wikipedia

[[Category:Nonfiction (nonfiction)]]
[[Category:Machines (nonfiction)]]
[[Category:Information systems (nonfiction)]]