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155-502: The Electric Telegraph Company ( ETC ) was a British telegraph company founded in 1846 by William Fothergill Cooke and John Ricardo . It was the world's first public telegraph company. The equipment used was the Cooke and Wheatstone telegraph , an electrical telegraph developed a few years earlier in collaboration with Charles Wheatstone . The system had been taken up by several railway companies for signalling purposes, but in forming

310-561: A diplomatic cable , is a confidential communication between a diplomatic mission and the foreign ministry of its parent country. These continue to be called telegrams or cables regardless of the method used for transmission. Passing messages by signalling over distance is an ancient practice. One of the oldest examples is the signal towers of the Great Wall of China . In 400 BC , signals could be sent by beacon fires or drum beats . By 200 BC complex flag signalling had developed, and by

465-462: A diversity scheme against damage from anchors and fishing gear. All four were combined into a single cable in the sea a short distance from landing. The work was begun in 1853 with the ship Monarch , specially purchased and fitted out for the purpose, and completed in 1854. The cable proved to need a great deal of maintenance and was replaced in 1858 by a single, heavier cable made by Glass, Elliot & Co and laid by William Cory . The Monarch

620-401: A form factor that allows compactly installing many relays in a control panel. Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller (PLC) mostly displaced the machine tool relay from sequential control applications. A relay allows circuits to be switched by electrical equipment: for example, a timer circuit with

775-478: A thermocouple or resistance thermometer sensor embedded in the winding. A polarized relay places the armature between the poles of a permanent magnet to increase sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and correct telegraphic distortion . A reed relay is a reed switch enclosed in a solenoid. The switch has a set of contacts inside an evacuated or inert gas -filled glass tube that protects

930-470: A voltage spike dangerous to semiconductor circuit components. Such diodes were not widely used before the application of transistors as relay drivers, but soon became ubiquitous as early germanium transistors were easily destroyed by this surge. Some automotive relays include a diode inside the relay case. Resistors, while more durable than diodes, are less efficient at eliminating voltage spikes generated by relays and therefore not as commonly used. If

1085-428: A circuit by an independent low-power signal, or where several circuits must be controlled by one signal. Relays were first used in long-distance telegraph circuits as signal repeaters: they refresh the signal coming in from one circuit by transmitting it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations. The traditional electromechanical form of

1240-448: A code by itself. The term heliostat is sometimes used as a synonym for heliograph because of this origin. The Colomb shutter ( Bolton and Colomb , 1862) was originally invented to enable the transmission of morse code by signal lamp between Royal Navy ships at sea. The heliograph was heavily used by Nelson A. Miles in Arizona and New Mexico after he took over command (1886) of

1395-586: A concession from Belgium for telegraph lines covering the whole country. The company installed a line from Brussels to Antwerp but the traffic was light (mainly stock exchange business) and the company decided to return its concession to the Belgian Government in 1850. In 1848, after a dispute with the Great Western over an engine the ETC was alleged to have damaged, the telegraph line from Paddington to Slough

1550-489: A convenient means of generating fast rise time pulses, however although the rise time may be picoseconds, the exact timing of the event is, like all other types of relay, subject to considerable jitter, possibly milliseconds, due to mechanical variations. The same coalescence process causes another effect, which is a nuisance in some applications. The contact resistance is not stable immediately after contact closure, and drifts, mostly downwards, for several seconds after closure,

1705-412: A director of several railway companies. The collaboration between Cooke and Charles Wheatstone in developing the Cooke and Wheatstone telegraph was not a happy one, degenerating into a bitter dispute over who had invented the telegraph. As a result, the company was formed without Wheatstone (although he claimed he had been offered the post of scientific adviser). At creation the company purchased all

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1860-410: A distance and cablegram means something written via a cable, whereas telegraph implies the process of writing at a distance. Later, a Telex was a message sent by a Telex network, a switched network of teleprinters similar to a telephone network. A wirephoto or wire picture was a newspaper picture that was sent from a remote location by a facsimile telegraph . A diplomatic telegram, also known as

2015-466: A distance of a quarter of a mile. In the 1890s inventor Nikola Tesla worked on an air and ground conduction wireless electric power transmission system , similar to Loomis', which he planned to include wireless telegraphy. Tesla's experiments had led him to incorrectly conclude that he could use the entire globe of the Earth to conduct electrical energy and his 1901 large scale application of his ideas,

2170-411: A feedback loop or sequential circuit . Such an electrically latching relay requires continuous power to maintain state, unlike magnetically latching relays or mechanically ratcheting relays. While (self-)holding circuits are often realized with relays they can also be implemented by other means. In computer memories, latching relays and other relays were replaced by delay-line memory , which in turn

2325-473: A few days, sometimes taking all day to send a message despite the use of the highly sensitive mirror galvanometer developed by William Thomson (the future Lord Kelvin ) before being destroyed by applying too high a voltage. Its failure and slow speed of transmission prompted Thomson and Oliver Heaviside to find better mathematical descriptions of long transmission lines . The company finally succeeded in 1866 with an improved cable laid by SS Great Eastern ,

2480-405: A fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity

2635-437: A good conductor. Contactors with overload protection devices are often used to start motors. A force-guided contacts relay has relay contacts that are mechanically linked together, so that when the relay coil is energized or de-energized, all of the linked contacts move together. If one set of contacts in the relay becomes immobilized, no other contact of the same relay will be able to move. The function of force-guided contacts

2790-404: A high-voltage wireless power station, now called Wardenclyffe Tower , lost funding and was abandoned after a few years. Telegraphic communication using earth conductivity was eventually found to be limited to impractically short distances, as was communication conducted through water, or between trenches during World War I. Electric relay Relays are used where it is necessary to control

2945-464: A leading figure in convincing them of its benefits. However, these systems were all for the exclusive use of the railway company concerned, mostly for signalling purposes, until 1843 when Cooke extended the Great Western Railway 's telegraph on to Slough at his own expense, at which point he acquired the right to open it to the public. Railway telegraphy continued to be an important part of

3100-540: A message was relayed 640 km (400 mi) in four hours. Miles' enemies used smoke signals and flashes of sunlight from metal, but lacked a sophisticated telegraph code. The heliograph was ideal for use in the American Southwest due to its clear air and mountainous terrain on which stations could be located. It was found necessary to lengthen the morse dash (which is much shorter in American Morse code than in

3255-489: A modification of surveying equipment ( Gauss , 1821). Various uses of mirrors were made for communication in the following years, mostly for military purposes, but the first device to become widely used was a heliograph with a moveable mirror ( Mance , 1869). The system was used by the French during the 1870–71 siege of Paris , with night-time signalling using kerosene lamps as the source of light. An improved version (Begbie, 1870)

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3410-592: A natural rubber from the Palaquium gutta tree, after William Montgomerie sent samples to London from Singapore in 1843. The new material was tested by Michael Faraday and in 1845 Wheatstone suggested that it should be used on the cable planned between Dover and Calais by John Watkins Brett . The idea was proved viable when the South Eastern Railway company successfully tested a three-kilometre (two-mile) gutta-percha insulated cable with telegraph messages to

3565-410: A new contract with Great Western which was extending its line to Exeter and Plymouth and by 1852 the ETC had installed a line that ran from London, past Slough, as far as Bristol . These contracts usually gave the company exclusive rights to install telegraph lines. This gave the company a significant advantage over competitors when other companies entered the market. Other areas of growth were in

3720-591: A non-infringing system, generating the telegraph pulses electromagnetically by the operator's own motion of working the equipment handles. The Magnetic got around the ETC's dominance of rail wayleaves by using buried cables along highways, a problem that had hindered the BETC and eventually led to its takeover by the Magnetic. Further, it had an exclusive agreement with the Submarine Telegraph Company who had laid

3875-458: A relay could switch power at a preset time. For many years relays were the standard method of controlling industrial electronic systems. A number of relays could be used together to carry out complex functions ( relay logic ). The principle of relay logic is based on relays which energize and de-energize associated contacts. Relay logic is the predecessor of ladder logic , which is commonly used in programmable logic controllers . A mercury relay

4030-574: A relay uses an electromagnet to close or open the contacts, but relays using other operating principles have also been invented, such as in solid-state relays which use semiconductor properties for control without relying on moving parts . Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called protective relays or safety relays . Latching relays require only

4185-447: A relay with several normally closed (NC) contacts may stick to the unenergized position, so that when energized, the circuit through one set of contacts is broken, with a marginal gap, while the other remains closed. By introducing both NO and NC contacts, or more commonly, changeover contacts, on the same relay, it then becomes possible to guarantee that if any NC contact is closed, all NO contacts are open, and conversely, if any NO contact

4340-596: A ship off the coast of Folkestone . The cable to France was laid in 1850 but was almost immediately severed by a French fishing vessel. It was relaid the next year and connections to Ireland and the Low Countries soon followed. Getting a cable across the Atlantic Ocean proved much more difficult. The Atlantic Telegraph Company , formed in London in 1856, had several failed attempts. A cable laid in 1858 worked poorly for

4495-475: A single pulse of control power to operate the switch persistently. Another pulse applied to a second set of control terminals, or a pulse with opposite polarity, resets the switch, while repeated pulses of the same kind have no effects. Magnetic latching relays are useful in applications when interrupted power should not affect the circuits that the relay is controlling. Electrical relays got their start in application to telegraphs . American scientist Joseph Henry

4650-440: A single-needle telegraph was adapted to indicate just two messages: "Line Clear" and "Line Blocked". The signaller would adjust his line-side signals accordingly. As first implemented in 1844 each station had as many needles as there were stations on the line, giving a complete picture of the traffic. As lines expanded, a sequence of pairs of single-needle instruments were adopted, one pair for each block in each direction. Wigwag

4805-640: A substantial distance was by Ronalds in 1816 using an electrostatic generator . Ronalds offered his invention to the British Admiralty , but it was rejected as unnecessary, the existing optical telegraph connecting the Admiralty in London to their main fleet base in Portsmouth being deemed adequate for their purposes. As late as 1844, after the electrical telegraph had come into use, the Admiralty's optical telegraph

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4960-418: A system for mass distributing information on current price of publicly listed companies. In a punched-tape system, the message is first typed onto punched tape using the code of the telegraph system—Morse code for instance. It is then, either immediately or at some later time, run through a transmission machine which sends the message to the telegraph network. Multiple messages can be sequentially recorded on

5115-503: A system of communication that would allow the central government to receive intelligence and to transmit orders in the shortest possible time. On 2 March 1791, at 11 am, they sent the message "si vous réussissez, vous serez bientôt couverts de gloire" (If you succeed, you will soon bask in glory) between Brulon and Parce, a distance of 16 kilometres (10 mi). The first means used a combination of black and white panels, clocks, telescopes, and codebooks to send their message. In 1792, Claude

5270-534: A telefax machine. In 1855, an Italian priest, Giovanni Caselli , also created an electric telegraph that could transmit images. Caselli called his invention " Pantelegraph ". Pantelegraph was successfully tested and approved for a telegraph line between Paris and Lyon . In 1881, English inventor Shelford Bidwell constructed the scanning phototelegraph that was the first telefax machine to scan any two-dimensional original, not requiring manual plotting or drawing. Around 1900, German physicist Arthur Korn invented

5425-461: A telegraph between St Petersburg and Kronstadt , but it was never completed. The first operative electric telegraph ( Gauss and Weber , 1833) connected Göttingen Observatory to the Institute of Physics about 1 km away during experimental investigations of the geomagnetic field. The first commercial telegraph was by Cooke and Wheatstone following their English patent of 10 June 1837. It

5580-566: A telegraph connection to the Netherlands between Orfordness and Scheveningen using submarine telegraph cables . The concession to lay the cables had originally been granted to the ETC, but the Dutch government objected to the ETC laying landlines on its territory so a separate company, the ITC, was set up to do this. In practice, the ITC was run by ETC staff. It planned to lay four separate cable cores as

5735-404: A thin, self-renewing film of liquid mercury. For higher-power relays switching many amperes, such as motor circuit contactors, contacts are made with a mixtures of silver and cadmium oxide, providing low contact resistance and high resistance to the heat of arcing. Contacts used in circuits carrying scores or hundreds of amperes may include additional structures for heat dissipation and management of

5890-418: A typical EN 50005-compliant SPDT relay's terminals would be numbered 11, 12, 14, A1 and A2 for the C, NC, NO, and coil connections, respectively. DIN 72552 defines contact numbers in relays for automotive use: Where radio transmitters and receivers share one antenna, often a coaxial relay is used as a TR (transmit-receive) relay, which switches the antenna from the receiver to the transmitter. This protects

6045-465: Is a form of flag signalling using a single flag. Unlike most forms of flag signalling, which are used over relatively short distances, wigwag is designed to maximise the distance covered—up to 32 km (20 mi) in some cases. Wigwag achieved this by using a large flag—a single flag can be held with both hands unlike flag semaphore which has a flag in each hand—and using motions rather than positions as its symbols since motions are more easily seen. It

6200-435: Is a relay that uses mercury as the switching element. They are used where contact erosion would be a problem for conventional relay contacts. Owing to environmental considerations about significant amount of mercury used and modern alternatives, they are now comparatively uncommon. A mercury-wetted reed relay is a form of reed relay that employs a mercury switch , in which the contacts are wetted with mercury . Mercury reduces

6355-512: Is a telegraph consisting of a line of stations in towers or natural high points which signal to each other by means of shutters or paddles. Signalling by means of indicator pointers was called semaphore . Early proposals for an optical telegraph system were made to the Royal Society by Robert Hooke in 1684 and were first implemented on an experimental level by Sir Richard Lovell Edgeworth in 1767. The first successful optical telegraph network

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6510-458: Is a telegraph machine that can send messages from a typewriter-like keyboard and print incoming messages in readable text with no need for the operators to be trained in the telegraph code used on the line. It developed from various earlier printing telegraphs and resulted in improved transmission speeds. The Morse telegraph (1837) was originally conceived as a system marking indentations on paper tape. A chemical telegraph making blue marks improved

6665-560: Is a telegraph system using reflected sunlight for signalling. It was mainly used in areas where the electrical telegraph had not been established and generally used the same code. The most extensive heliograph network established was in Arizona and New Mexico during the Apache Wars . The heliograph was standard military equipment as late as World War II . Wireless telegraphy developed in the early 20th century became important for maritime use, and

6820-457: Is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage application this reduces noise; in a high voltage or current application it reduces arcing . When the coil is energized with direct current , a flyback diode or snubber resistor is often placed across the coil to dissipate the energy from the collapsing magnetic field ( back EMF ) at deactivation, which would otherwise generate

6975-627: Is closed, all NC contacts are open. It is not possible to reliably ensure that any particular contact is closed, except by potentially intrusive and safety-degrading sensing of its circuit conditions, however in safety systems it is usually the NO state that is most important, and as explained above, this is reliably verifiable by detecting the closure of a contact of opposite sense. Force-guided contact relays are made with different main contact sets, either NO, NC or changeover, and one or more auxiliary contact sets, often of reduced current or voltage rating, used for

7130-412: Is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of

7285-534: Is needed. A stepping relay is a specialized kind of multi-way latching relay designed for early automatic telephone exchanges . An earth-leakage circuit breaker includes a specialized latching relay. Very early computers often stored bits in a magnetically latching relay, such as ferreed or the later remreed in the 1ESS switch . Some early computers used ordinary relays as a kind of latch —they store bits in ordinary wire-spring relays or reed relays by feeding an output wire back as an input, resulting in

7440-442: Is often cited to have invented a relay in 1835 in order to improve his version of the electrical telegraph , developed earlier in 1831. However, an official patent was not issued until 1840 to Samuel Morse for his telegraph, which is now called a relay. The mechanism described acted as a digital amplifier, repeating the telegraph signal, and thus allowing signals to be propagated as far as desired. The word relay appears in

7595-407: Is partly offset by the increased costs in the external circuit. In another type, a ratchet relay has a ratchet mechanism that holds the contacts closed after the coil is momentarily energized. A second impulse, in the same or a separate coil, releases the contacts. This type may be found in certain cars, for headlamp dipping and other functions where alternating operation on each switch actuation

7750-400: Is present; changing the orientation of the reeds or degaussing the switch with respect to the solenoid's magnetic field can resolve this problem. Sealed contacts with mercury-wetted contacts have longer operating lives and less contact chatter than any other kind of relay. Safety relays are devices which generally implement protection functions. In the event of a hazard, the task of such

7905-447: Is that it permits duplex communication. The Wheatstone tape reader was capable of a speed of 400 words per minute. A worldwide communication network meant that telegraph cables would have to be laid across oceans. On land cables could be run uninsulated suspended from poles. Underwater, a good insulator that was both flexible and capable of resisting the ingress of seawater was required. A solution presented itself with gutta-percha ,

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8060-438: Is to enable the safety circuit to check the status of the relay. Force-guided contacts are also known as "positive-guided contacts", "captive contacts", "locked contacts", "mechanically linked contacts", or "safety relays". These safety relays have to follow design rules and manufacturing rules that are defined in one main machinery standard EN 50205 : Relays with forcibly guided (mechanically linked) contacts. These rules for

8215-519: Is used to split the flux into two out-of-phase components which add together, increasing the minimum pull on the armature during the AC cycle. Typically this is done with a small copper "shading ring" crimped around a portion of the core that creates the delayed, out-of-phase component, which holds the contacts during the zero crossings of the control voltage. Contact materials for relays vary by application. Materials with low contact resistance may be oxidized by

8370-625: The Bildtelegraph widespread in continental Europe especially since a widely noticed transmission of a wanted-person photograph from Paris to London in 1908 used until the wider distribution of the radiofax. Its main competitors were the Bélinographe by Édouard Belin first, then since the 1930s, the Hellschreiber , invented in 1929 by German inventor Rudolf Hell , a pioneer in mechanical image scanning and transmission. The late 1880s through to

8525-648: The English Channel (1899), from shore to ship (1899) and finally across the Atlantic (1901). A study of these demonstrations of radio, with scientists trying to work out how a phenomenon predicted to have a short range could transmit "over the horizon", led to the discovery of a radio reflecting layer in the Earth's atmosphere in 1902, later called the ionosphere . Radiotelegraphy proved effective for rescue work in sea disasters by enabling effective communication between ships and from ship to shore. In 1904, Marconi began

8680-499: The First Macedonian War . Nothing else that could be described as a true telegraph existed until the 17th century. Possibly the first alphabetic telegraph code in the modern era is due to Franz Kessler who published his work in 1616. Kessler used a lamp placed inside a barrel with a moveable shutter operated by the signaller. The signals were observed at a distance with the newly invented telescope. An optical telegraph

8835-634: The General Post Office (GPO). She was then relegated to a coal hulk . The chief competitor to the company, the Magnetic, had succeeded in providing the first connection to Ireland in 1853 on the Portpatrick–Donaghadee route. The ETC was keen to establish its own connection. In September 1854 Monarch attempted to lay a lightweight cable from Holyhead in Wales to Howth in Ireland. This attempt

8990-561: The General Post Office . The Electric Telegraph Company was the world's first public telegraph company, founded in the United Kingdom in 1846 by Sir William Fothergill Cooke and John Lewis Ricardo , MP for Stoke-on-Trent , with Cromwell F. Varley as chief engineer. Its headquarters was in Founders Court, Lothbury , behind the Bank of England . This was the first company formed for

9145-582: The Han dynasty (200 BC – 220 AD) signallers had a choice of lights, flags, or gunshots to send signals. By the Tang dynasty (618–907) a message could be sent 1,100 kilometres (700 mi) in 24 hours. The Ming dynasty (1368–1644) added artillery to the possible signals. While the signalling was complex (for instance, different-coloured flags could be used to indicate enemy strength), only predetermined messages could be sent. The Chinese signalling system extended well beyond

9300-456: The London and Birmingham Railway line's chief engineer. The messages were for the operation of the rope-haulage system for pulling trains up the 1 in 77 bank. The world's first permanent railway telegraph was completed in July 1839 between London Paddington and West Drayton on the Great Western Railway with an electric telegraph using a four-needle system. The concept of a signalling "block" system

9455-462: The tidal race between Portland Bill and the Isle of Portland . The main section was finally abandoned as a maintenance liability shortly after September 1860. A subsidiary company, the Isle of Man Electric Telegraph Company was formed in 1859 for the purpose of providing telegraph to the Isle of Man . The cable was made by Glass, Elliot & Co and laid by Resolute from Whitehaven . The company

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9610-465: The 1850s until well into the 20th century, British submarine cable systems dominated the world system. This was set out as a formal strategic goal, which became known as the All Red Line . In 1896, there were thirty cable-laying ships in the world and twenty-four of them were owned by British companies. In 1892, British companies owned and operated two-thirds of the world's cables and by 1923, their share

9765-530: The 1890s saw the discovery and then development of a newly understood phenomenon into a form of wireless telegraphy , called Hertzian wave wireless telegraphy, radiotelegraphy, or (later) simply " radio ". Between 1886 and 1888, Heinrich Rudolf Hertz published the results of his experiments where he was able to transmit electromagnetic waves (radio waves) through the air, proving James Clerk Maxwell 's 1873 theory of electromagnetic radiation . Many scientists and inventors experimented with this new phenomenon but

9920-525: The British government followed—by March 1897, Marconi had transmitted Morse code signals over a distance of about 6 km ( 3 + 1 ⁄ 2  mi) across Salisbury Plain . On 13 May 1897, Marconi, assisted by George Kemp, a Cardiff Post Office engineer, transmitted the first wireless signals over water to Lavernock (near Penarth in Wales) from Flat Holm . His star rising, he was soon sending signals across

10075-610: The Electric Telegraph Company (33 volumes), 1846–1872, the International Telegraph Company (5 volumes), 1852–1858 and the Electric and International Telegraph Company (62 volumes), [1852]–1905 are held by BT Archives . 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

10230-630: The Great Wall. Signal towers away from the wall were used to give early warning of an attack. Others were built even further out as part of the protection of trade routes, especially the Silk Road . Signal fires were widely used in Europe and elsewhere for military purposes. The Roman army made frequent use of them, as did their enemies, and the remains of some of the stations still exist. Few details have been recorded of European/Mediterranean signalling systems and

10385-462: The Morse system connected Baltimore to Washington , and by 1861 the west coast of the continent was connected to the east coast. The Cooke and Wheatstone telegraph , in a series of improvements, also ended up with a one-wire system, but still using their own code and needle displays . The electric telegraph quickly became a means of more general communication. The Morse system was officially adopted as

10540-547: The Relay and Switch Industry Association define 23 distinct electrical contact forms found in relays and switches. Of these, the following are commonly encountered: The S ( single ) or D ( double ) designator for the pole count may be replaced with a number, indicating multiple contacts connected to a single actuator . For example, 4PDT indicates a four-pole double-throw relay that has 12 switching terminals. EN 50005 are among applicable standards for relay terminal numbering;

10695-678: The Submarine Telegraph Company and the Magnetic for cable work. The first charter was to R.S. Newall and Company to recover an abandoned cable in the Irish Sea. Newall had made this cable for the Magnetic and a failed attempt to lay it from Portpatrick in Scotland to Donaghadee in Ireland was made in 1852. Newall temporarily installed its own picking-up machine as Webb's had not yet been fitted. After nationalisation in 1870, Monarch irreparably broke down on her first cable mission for

10850-539: The air, or may tend to "stick" instead of cleanly parting when opening. Contact material may be optimized for low electrical resistance, high strength to withstand repeated operations, or high capacity to withstand the heat of an arc. Where very low resistance is required, or low thermally-induced voltages are desired, gold-plated contacts may be used, along with palladium and other non-oxidizing, semi-precious metals. Silver or silver-plated contacts are used for signal switching. Mercury-wetted relays make and break circuits using

11005-463: The arc produced when interrupting the circuit. Some relays have field-replaceable contacts, such as certain machine tool relays; these may be replaced when worn out, or changed between normally open and normally closed state, to allow for changes in the controlled circuit. Since relays are switches , the terminology applied to switches is also applied to relays; a relay switches one or more poles , each of whose contacts can be thrown by energizing

11160-458: The change perhaps being 0.5 ohm. Multi-voltage relays are devices designed to work for wide voltage ranges such as 24 to 240 VAC and VDC and wide frequency ranges such as 0 to 300 Hz. They are indicated for use in installations that do not have stable supply voltages. Electric motors need overcurrent protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in

11315-449: The circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke , which is soldered to the PCB. When an electric current is passed through the coil it generates a magnetic field that activates the armature, and the consequent movement of the movable contact(s) either makes or breaks (depending upon construction) a connection with

11470-421: The coil. Normally open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. Normally closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. All of the contact forms involve combinations of NO and NC connections. The National Association of Relay Manufacturers and its successor,

11625-405: The coil. The advantage is that one coil consumes power only for an instant while the relay is being switched, and the relay contacts retain this setting across a power outage. A latching relay allows remote control of building lighting without the hum that may be produced from a continuously (AC) energized coil. In one mechanism, two opposing coils with an over-center spring or permanent magnet hold

11780-529: The company Cooke intended to open up the technology to the public at large. The ETC had a monopoly of electrical telegraphy until the formation of the Magnetic Telegraph Company (commonly called the Magnetic ) who used a different system which did not infringe the ETC's patents. The Magnetic became the chief rival of the ETC and the two of them dominated the market even after further companies entered

11935-557: The company to relocate its London central office to Great Bell Alley, Moorgate , but retaining the Founders Court site as a public office. The Moorgate office was arranged over three floors and a large number of men and boys were recruited on an accelerating rate of pay. The company also employed a significant number of women from a higher social class as telegraphists operating the Wheatstone needle instruments. They were paid less and they had to leave if they married. A notable early employee

12090-453: The company's business with expenditure on the railways peaking in 1847–48. This focus on the railways was reflected in the directors and major shareholders being dominated by people associated with railway construction. Additional railway people who had become involved by 1849 included Samuel Morton Peto , Thomas Brassey , Robert Stephenson (of Rocket fame and who was chairman of the company in 1857–58), Joseph Paxton , and Richard Till,

12245-483: The company's existence, but printing telegraphs were also in use by the 1850s. From 1867, the ETC started to use the Wheatstone automatic duplex system . This device sent messages at an extremely fast rate from text that had been prerecorded on paper punched tape . Its advantage was that it could make maximum use of a telegraph line. This had a great economic advantage on busy long-distance lines where traffic capacity

12400-438: The consensus was that these new waves (similar to light) would be just as short range as light, and, therefore, useless for long range communication. At the end of 1894, the young Italian inventor Guglielmo Marconi began working on the idea of building a commercial wireless telegraphy system based on the use of Hertzian waves (radio waves), a line of inquiry that he noted other inventors did not seem to be pursuing. Building on

12555-525: The contact resistance and mitigates the associated voltage drop. Surface contamination may result in poor conductivity for low-current signals. For high-speed applications, the mercury eliminates contact bounce, and provides virtually instantaneous circuit closure. Mercury wetted relays are position-sensitive and must be mounted according to the manufacturer's specifications. Because of the toxicity and expense of liquid mercury, these relays have increasingly fallen into disuse. The high speed of switching action of

12710-479: The contacts against atmospheric corrosion ; the contacts are made of magnetic material that makes them move under the influence of the field of the enclosing solenoid or an external magnet. Reed relays can switch faster than larger relays and require very little power from the control circuit. However, they have relatively low switching current and voltage ratings. Though rare, the reeds can become magnetized over time, which makes them stick "on", even when no current

12865-411: The contacts in position after the coil is de-energized. A pulse to one coil turns the relay on, and a pulse to the opposite coil turns the relay off. This type is widely used where control is from simple switches or single-ended outputs of a control system, and such relays are found in avionics and numerous industrial applications. Another latching type has a remanent core that retains the contacts in

13020-546: The contacts. To prevent short over current spikes from causing nuisance triggering the armature movement is damped with a dashpot . The thermal and magnetic overload detections are typically used together in a motor protection relay. Electronic overload protection relays measure motor current and can estimate motor winding temperature using a "thermal model" of the motor armature system that can be set to provide more accurate motor protection. Some motor protection relays include temperature detector inputs for direct measurement from

13175-460: The context of electromagnetic operations from 1860 onwards. A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core (a solenoid), an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature , and one or more sets of contacts (there are two contacts in the relay pictured). The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. The armature

13330-411: The coordinates of the letter of the alphabet being transmitted. The number of said torches held up signalled the grid square that contained the letter. There is no definite record of the system ever being used, but there are several passages in ancient texts that some think are suggestive. Holzmann and Pehrson, for instance, suggest that Livy is describing its use by Philip V of Macedon in 207 BC during

13485-458: The earliest electrical telegraphs. A telegraph message sent by an electrical telegraph operator or telegrapher using Morse code (or a printing telegraph operator using plain text) was known as a telegram. A cablegram was a message sent by a submarine telegraph cable, often shortened to "cable" or "wire". The suffix -gram is derived from ancient Greek: γραμμα ( gramma ), meaning something written, i.e. telegram means something written at

13640-531: The erroneous belief that there was an electrified atmospheric stratum accessible at low altitude. They thought atmosphere current, connected with a return path using "Earth currents" would allow for wireless telegraphy as well as supply power for the telegraph, doing away with artificial batteries. A more practical demonstration of wireless transmission via conduction came in Amos Dolbear 's 1879 magneto electric telephone that used ground conduction to transmit over

13795-415: The extensive definition used by Chappe, Morse argued that the term telegraph can strictly be applied only to systems that transmit and record messages at a distance. This is to be distinguished from semaphore , which merely transmits messages. Smoke signals, for instance, are to be considered semaphore, not telegraph. According to Morse, telegraph dates only from 1832 when Pavel Schilling invented one of

13950-549: The field. The ETC was heavily involved in laying submarine telegraph cables , including lines to the Netherlands , Ireland , the Channel Islands , and the Isle of Man . It operated the world's first specialised cable-laying ship, the Monarch . A private line was laid for Queen Victoria on the Isle of Wight . The company was nationalised in 1870 along with other British telegraph companies, and its assets were taken over by

14105-500: The fight against Geronimo and other Apache bands in the Apache Wars . Miles had previously set up the first heliograph line in the US between Fort Keogh and Fort Custer in Montana . He used the heliograph to fill in vast, thinly populated areas that were not covered by the electric telegraph. Twenty-six stations covered an area 320 by 480 km (200 by 300 mi). In a test of the system,

14260-406: The first cable to France and was busily laying more cables to other continental countries. The Magnetic also beat the ETC in getting the first cable to Ireland in 1853. For a while then, the Magnetic had shut the ETC out of international business. The ETC was keen to correct this situation and started laying its own submarine cables. Other companies came on to the market, but ETC remained by far

14415-618: The first commercial service to transmit nightly news summaries to subscribing ships, which could incorporate them into their on-board newspapers. A regular transatlantic radio-telegraph service was finally begun on 17 October 1907. Notably, Marconi's apparatus was used to help rescue efforts after the sinking of RMS  Titanic . Britain's postmaster-general summed up, referring to the Titanic disaster, "Those who have been saved, have been saved through one man, Mr. Marconi...and his marvellous invention." The successful development of radiotelegraphy

14570-527: The fore hold and the main hold for this reason. Besides the cables to the Netherlands, Monarch laid several cables around Britain in its first year. One of these was a cable across the Solent to the Isle of Wight . The purpose of this cable was to provide a connection to Osborne House , the summer residence of Queen Victoria . A number of improvements were made to Monarch over the years and its gear became

14725-696: The ground without any wires connecting the stations. Other attempts were made to send the electric current through bodies of water, to span rivers, for example. Prominent experimenters along these lines included Samuel F. B. Morse in the United States and James Bowman Lindsay in Great Britain, who in August 1854, was able to demonstrate transmission across a mill dam at a distance of 500 yards (457 metres). US inventors William Henry Ward (1871) and Mahlon Loomis (1872) developed electrical conduction systems based on

14880-419: The ideas of previous scientists and inventors Marconi re-engineered their apparatus by trial and error attempting to build a radio-based wireless telegraphic system that would function the same as wired telegraphy. He would work on the system through 1895 in his lab and then in field tests making improvements to extend its range. After many breakthroughs, including applying the wired telegraphy concept of grounding

15035-583: The largest component of the resulting state monopoly run by the GPO. In 1969 Post Office Telecommunications was made a distinct department of the Post Office, and in 1981 it was separated entirely from the Post Office as British Telecom . In 1984, British Telecom was privatised and from 1991 traded as BT . The primary system initially used by the company was the two-needle and one-needle Cooke and Wheatstone telegraphs. Needle telegraphs continued to be used throughout

15190-530: The largest of them with the Magnetic second. The ETC and the Magnetic so dominated the market that they were virtually a duopoly until nationalisation. The Electric Telegraph Company merged with the International Telegraph Company (ITC) in 1854 to become the Electric and International Telegraph Company . The International Telegraph Company had been formed in 1853 for the purpose of establishing

15345-545: The largest ship of its day, designed by Isambard Kingdom Brunel . An overland telegraph from Britain to India was first connected in 1866 but was unreliable so a submarine telegraph cable was connected in 1870. Several telegraph companies were combined to form the Eastern Telegraph Company in 1872. Australia was first linked to the rest of the world in October 1872 by a submarine telegraph cable at Darwin . From

15500-415: The letter post on price, and competition from the telephone , which removed their speed advantage, drove the telegraph into decline from 1920 onwards. The few remaining telegraph applications were largely taken over by alternatives on the internet towards the end of the 20th century. The word telegraph (from Ancient Greek : τῆλε ( têle ) 'at a distance' and γράφειν ( gráphein ) 'to write')

15655-421: The line at his own expense and agreed that the railway could have free use of it in exchange for the right to open it up to the public. Most of the early electrical systems required multiple wires (Ronalds' system was an exception), but the system developed in the United States by Morse and Vail was a single-wire system. This was the system that first used the soon-to-become-ubiquitous Morse code . By 1844,

15810-407: The mercury-wetted relay is a notable advantage. The mercury globules on each contact coalesce , and the current rise time through the contacts is generally considered to be a few picoseconds. However, in a practical circuit it may be limited by the inductance of the contacts and wiring. It was quite common, before restrictions on the use of mercury, to use a mercury-wetted relay in the laboratory as

15965-451: 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

16120-609: The modern International Morse code) to aid differentiating from the morse dot. Use of the heliograph declined from 1915 onwards, but remained in service in Britain and British Commonwealth countries for some time. Australian forces used the heliograph as late as 1942 in the Western Desert Campaign of World War II . Some form of heliograph was used by the mujahideen in the Soviet–Afghan War (1979–1989). A teleprinter

16275-456: The monitoring system. Contacts may be all NO, all NC, changeover, or a mixture of these, for the monitoring contacts, so that the safety system designer can select the correct configuration for the particular application. Safety relays are used as part of an engineered safety system. A latching relay, also called impulse , bistable , keep , or stay relay, or simply latch , maintains either contact position indefinitely without power applied to

16430-415: The motor windings. The overload sensing devices are a form of heat operated relay where a coil heats a bimetallic strip , or where a solder pot melts, to operate auxiliary contacts. These auxiliary contacts are in series with the motor's contactor coil, so they turn off the motor when it overheats. This thermal protection operates relatively slowly allowing the motor to draw higher starting currents before

16585-527: The operated position by the remanent magnetism in the core. This type requires a current pulse of opposite polarity to release the contacts. A variation uses a permanent magnet that produces part of the force required to close the contact; the coil supplies sufficient force to move the contact open or closed by aiding or opposing the field of the permanent magnet. A polarity controlled relay needs changeover switches or an H-bridge drive circuit to control it. The relay may be less expensive than other types, but this

16740-457: The patents Cooke and Wheatstone had obtained to date in building the Cooke and Wheatstone telegraph. It also obtained the important patent for the electric relay from Edward Davy for £600. The relay allowed telegraph signals weakened over a long distance to be renewed and retransmitted onward. The company was not immediately hugely profitable, and shares were more or less worthless. In 1846 it won

16895-399: The possible messages. One of the few for which details are known is a system invented by Aeneas Tacticus (4th century BC). Tacticus's system had water filled pots at the two signal stations which were drained in synchronisation. Annotation on a floating scale indicated which message was being sent or received. Signals sent by means of torches indicated when to start and stop draining to keep

17050-418: The protection relay will trip. Where the overload relay is exposed to the same ambient temperature as the motor, a useful though crude compensation for motor ambient temperature is provided. The other common overload protection system uses an electromagnet coil in series with the motor circuit that directly operates contacts. This is similar to a control relay but requires a rather high fault current to operate

17205-411: The prototype for future cable ships. A cable picking-up machine was soon fitted with a drum that could be driven by both steam engine and manual winching, designed by the company engineer, Frederick Charles Webb . In 1857, draw-off gear was fitted to avoid crew having to hold the cable taught by hand, and water-cooled brakes were fitted in 1863. The ship was frequently chartered to other companies like

17360-420: The receiver from the high power of the transmitter. Such relays are often used in transceivers which combine transmitter and receiver in one unit. The relay contacts are designed not to reflect any radio frequency power back toward the source, and to provide very high isolation between receiver and transmitter terminals. The characteristic impedance of the relay is matched to the transmission line impedance of

17515-462: The relay is driving a large, or especially a reactive load, there may be a similar problem of surge currents around the relay output contacts. In this case a snubber circuit (a capacitor and resistor in series) across the contacts may absorb the surge. Suitably rated capacitors and the associated resistor are sold as a single packaged component for this commonplace use. If the coil is designed to be energized with alternating current (AC), some method

17670-478: The right to force the railways to allow the BETC to construct a telegraph for government use between Liverpool and London. The ETC tried to oppose the government Bill but without success. A more serious rival came in 1851 with the formation of the English and Irish Magnetic Telegraph Company (later renamed the British and Irish Magnetic Telegraph Company and usually just called the Magnetic ). The Magnetic also used

17825-569: The safety design are the one defined in type B standards such as EN 13849-2 as Basic safety principles and Well-tried safety principles for machinery that applies to all machines. Force-guided contacts by themselves can not guarantee that all contacts are in the same state, however, they do guarantee, subject to no gross mechanical fault, that no contacts are in opposite states. Otherwise, a relay with several normally open (NO) contacts may stick when energized, with some contacts closed and others still slightly open, due to mechanical tolerances. Similarly,

17980-419: The same run of tape. The advantage of doing this is that messages can be sent at a steady, fast rate making maximum use of the available telegraph lines. The economic advantage of doing this is greatest on long, busy routes where the cost of the extra step of preparing the tape is outweighed by the cost of providing more telegraph lines. The first machine to use punched tape was Bain's teleprinter (Bain, 1843), but

18135-519: The specific purpose of providing a telegraph service to the public. Besides Cooke and Ricardo, the original shareholders were railway engineer George Parker Bidder with the largest holding, Benjamin Hawes , Thomas Boulton, and three other members of the Ricardo family; Samson , Albert, and Frederick. Up to this point telegraph lines had been laid mostly in conjunction with railway companies, and Cooke had been

18290-451: The speed of recording ( Bain , 1846), but was delayed by a patent challenge from Morse. The first true printing telegraph (that is printing in plain text) used a spinning wheel of types in the manner of a daisy wheel printer ( House , 1846, improved by Hughes , 1855). The system was adopted by Western Union . Early teleprinters used the Baudot code , a five-bit sequential binary code. This

18445-520: The standard for continental European telegraphy in 1851 with a revised code, which later became the basis of International Morse Code . However, Great Britain and the British Empire continued to use the Cooke and Wheatstone system, in some places as late as the 1930s. Likewise, the United States continued to use American Morse code internally, requiring translation operators skilled in both codes for international messages. Railway signal telegraphy

18600-534: The supply of news to newspapers, and contracts with stock exchanges. However, general use by the public was retarded by the high cost of sending a message. By 1855 this situation was changing. The ETC now had over 5,200 miles of line and sent nearly three-quarters of a million messages that year. The growth, together with competitors coming on to the market, drove down prices. ETC's maximum charge for an inland telegram (over 100 miles) fell from ten shillings in 1851 to four shillings in 1855. By 1859, growth required

18755-462: The synchronisation. None of the signalling systems discussed above are true telegraphs in the sense of a system that can transmit arbitrary messages over arbitrary distances. Lines of signalling relay stations can send messages to any required distance, but all these systems are limited to one extent or another in the range of messages that they can send. A system like flag semaphore , with an alphabetic code, can certainly send any given message, but

18910-554: The system is designed for short-range communication between two persons. An engine order telegraph , used to send instructions from the bridge of a ship to the engine room, fails to meet both criteria; it has a limited distance and very simple message set. There was only one ancient signalling system described that does meet these criteria. That was a system using the Polybius square to encode an alphabet. Polybius (2nd century BC) suggested using two successive groups of torches to identify

19065-549: The system saw only limited use. Later versions of Bain's system achieved speeds up to 1000 words per minute, far faster than a human operator could achieve. The first widely used system (Wheatstone, 1858) was first put into service with the British General Post Office in 1867. A novel feature of the Wheatstone system was the use of bipolar encoding . That is, both positive and negative polarity voltages were used. Bipolar encoding has several advantages, one of which

19220-404: The system, for example, 50 ohms. A contactor is a heavy-duty relay with higher current ratings, used for switching electric motors and lighting loads. Continuous current ratings for common contactors range from 10 amps to several hundred amps. High-current contacts are made with alloys containing silver . The unavoidable arcing causes the contacts to oxidize; however, silver oxide is still

19375-462: The transmitter and receiver, Marconi was able, by early 1896, to transmit radio far beyond the short ranges that had been predicted. Having failed to interest the Italian government, the 22-year-old inventor brought his telegraphy system to Britain in 1896 and met William Preece , a Welshman, who was a major figure in the field and Chief Engineer of the General Post Office . A series of demonstrations for

19530-445: The two stations to form a complete electrical circuit or "loop". In 1837, however, Carl August von Steinheil of Munich , Germany , found that by connecting one leg of the apparatus at each station to metal plates buried in the ground, he could eliminate one wire and use a single wire for telegraphic communication. This led to speculation that it might be possible to eliminate both wires and therefore transmit telegraph signals through

19685-449: The unspecialised ships that had previously been used for cable laying, with sheaves to run the cable out of the hold and a powerful dedicated brake to control the cable running out. However, Monarch did not store the cable in water-filled tanks as was done on future cable ships. The ship could not, therefore, be kept in trim by replacing the cable with water as it was payed out. It was necessary to run out coils of cable alternately from

19840-532: Was Maria Craig who became a supervisor. The portion of Great Bell Alley east of Moorgate Street was later renamed Telegraph Street in recognition of the importance of the company at 11–14 Telegraph Street. The site is now occupied by The Telegraph pub. In the Act of Parliament establishing the company, the government reserved the right to take over the resources of the ETC in times of national emergency. This it did in 1848 in response to Chartist agitation. Chartism

19995-459: Was a competitor to electrical telegraphy using submarine telegraph cables in international communications. Telegrams became a popular means of sending messages once telegraph prices had fallen sufficiently. Traffic became high enough to spur the development of automated systems— teleprinters and punched tape transmission. These systems led to new telegraph codes , starting with the Baudot code . However, telegrams were never able to compete with

20150-410: Was a failure, as had previous attempts on both routes with lightweight cable. In June 1855 Monarch tried again, but this time with a heavier cable made by Newall. This attempt was successful, the cable being to a similar design to the one Newall had made for the successful Magnetic cable. Another cable was laid to Ireland in 1862, this time from Wexford in Ireland to Abermawr in Wales. The cable

20305-481: Was a telegraph code developed for use on the French telegraph using a five-key keyboard ( Baudot , 1874). Teleprinters generated the same code from a full alphanumeric keyboard. A feature of the Baudot code, and subsequent telegraph codes, was that, unlike Morse code, every character has a code of the same length making it more machine friendly. The Baudot code was used on the earliest ticker tape machines ( Calahan , 1867),

20460-456: Was a working-class movement for democratic reform. One of the main aims was to achieve the vote for all men over twenty-one. In April 1848, the Chartists organised a large demonstration at Kennington Common and presented a petition signed by millions. The government, fearing an insurrection, used its control of the ETC telegraph to disrupt Chartist communication. The first competitor to emerge

20615-469: Was appointed Ingénieur-Télégraphiste and charged with establishing a line of stations between Paris and Lille , a distance of 230 kilometres (140 mi). It was used to carry dispatches for the war between France and Austria. In 1794, it brought news of a French capture of Condé-sur-l'Escaut from the Austrians less than an hour after it occurred. A decision to replace the system with an electric telegraph

20770-401: Was coined by the French inventor of the semaphore telegraph , Claude Chappe , who also coined the word semaphore . A telegraph is a device for transmitting and receiving messages over long distances, i.e., for telegraphy. The word telegraph alone generally refers to an electrical telegraph . Wireless telegraphy is transmission of messages over radio with telegraphic codes. Contrary to

20925-414: Was demonstrated on the London and Birmingham Railway in July of the same year. In July 1839, a five-needle, five-wire system was installed to provide signalling over a record distance of 21 km on a section of the Great Western Railway between London Paddington station and West Drayton. However, in trying to get railway companies to take up his telegraph more widely for railway signalling , Cooke

21080-421: Was developed in Britain from the 1840s onward. It was used to manage railway traffic and to prevent accidents as part of the railway signalling system. On 12 June 1837 Cooke and Wheatstone were awarded a patent for an electric telegraph. This was demonstrated between Euston railway station —where Wheatstone was located—and the engine house at Camden Town—where Cooke was stationed, together with Robert Stephenson ,

21235-638: Was invented by Claude Chappe and operated in France from 1793. The two most extensive systems were Chappe's in France, with branches into neighbouring countries, and the system of Abraham Niclas Edelcrantz in Sweden. During 1790–1795, at the height of the French Revolution , France needed a swift and reliable communication system to thwart the war efforts of its enemies. In 1790, the Chappe brothers set about devising

21390-522: Was invented by US Army surgeon Albert J. Myer in the 1850s who later became the first head of the Signal Corps . Wigwag was used extensively during the American Civil War where it filled a gap left by the electrical telegraph. Although the electrical telegraph had been in use for more than a decade, the network did not yet reach everywhere and portable, ruggedized equipment suitable for military use

21545-616: Was limited by the speed of the operator. To increase traffic it would otherwise have been necessary to install expensive additional lines and employ additional operators. In 1854 the ETC installed a pneumatic tube system between its London central office and the London Stock Exchange using underground pipes. This system was later extended to other major company offices in London. Systems were also installed in Liverpool (1864), Birmingham (1865), and Manchester (1865). Records of

21700-498: Was made by Glass, Elliot & Co and laid by Berwick . A subsidiary company, the Channel Islands Telegraph Company was formed in 1857 for the purpose of providing telegraph to the Channel Islands of Jersey , Guernsey , and Alderney . The main cable was made by Newall and laid by Elba between Weymouth and Alderney in August 1858. The cable required numerous repairs due to the rocky coast of Alderney and

21855-782: Was made in 1846, but it took a decade before it was fully taken out of service. The fall of Sevastopol was reported by Chappe telegraph in 1855. The Prussian system was put into effect in the 1830s. However, they were highly dependent on good weather and daylight to work and even then could accommodate only about two words per minute. The last commercial semaphore link ceased operation in Sweden in 1880. As of 1895, France still operated coastal commercial semaphore telegraph stations, for ship-to-shore communication. The early ideas for an electric telegraph included in 1753 using electrostatic deflections of pith balls, proposals for electrochemical bubbles in acid by Campillo in 1804 and von Sömmering in 1809. The first experimental system over

22010-587: Was nationalised by the British government in 1870 under the Telegraph Act 1868 along with most other British telegraph companies. The Telegraph Act 1870 extended the 1868 Act to include the Isle of Man Electric Telegraph Company and the Jersey and Guernsey Telegraph Company , but excluded the Submarine Telegraph Company and other companies which exclusively operated international cables. The Electric Telegraph Company formed

22165-400: Was not immediately available. Permanent or semi-permanent stations were established during the war, some of them towers of enormous height and the system was extensive enough to be described as a communications network. A heliograph is a telegraph that transmits messages by flashing sunlight with a mirror, usually using Morse code. The idea for a telegraph of this type was first proposed as

22320-455: Was preceded by a 50-year history of ingenious but ultimately unsuccessful experiments by inventors to achieve wireless telegraphy by other means. Several wireless electrical signaling schemes based on the (sometimes erroneous) idea that electric currents could be conducted long-range through water, ground, and air were investigated for telegraphy before practical radio systems became available. The original telegraph lines used two wires between

22475-433: Was proposed by Cooke in 1842. Railway signal telegraphy did not change in essence from Cooke's initial concept for more than a century. In this system each line of railway was divided into sections or blocks of varying length. Entry to and exit from the block was to be authorised by electric telegraph and signalled by the line-side semaphore signals, so that only a single train could occupy the rails. In Cooke's original system,

22630-496: 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. The heliograph

22785-486: Was rejected several times in favour of the more familiar, but shorter range, steam-powered pneumatic signalling. Even when his telegraph was taken up, it was considered experimental and the company backed out of a plan to finance extending the telegraph line out to Slough . However, this led to a breakthrough for the electric telegraph, as up to this point the Great Western had insisted on exclusive use and refused Cooke permission to open public telegraph offices. Cooke extended

22940-492: Was removed, although the railway company continued to use the telegraph at the Box Tunnel . The setback with the Great Western did not slow the growth of the telegraph along railway lines, and these continued to be the main source of revenue. By 1848 the company had telegraph lines along half of the railway lines then open, some 1,800 miles, and continued to make deals with more railway companies after that. These included in 1851

23095-407: Was replaced by a series of ever faster and ever smaller memory technologies. A machine tool relay is a type standardized for industrial control of machine tools , transfer machines, and other sequential control. They are characterized by a large number of contacts (sometimes extendable in the field) which are easily converted from normally open to normally closed status, easily replaceable coils, and

23250-496: Was still 42.7 percent. During World War I , Britain's telegraph communications were almost completely uninterrupted while it was able to quickly cut Germany's cables worldwide. In 1843, Scottish inventor Alexander Bain invented a device that could be considered the first facsimile machine . He called his invention a "recording telegraph". Bain's telegraph was able to transmit images by electrical wires. Frederick Bakewell made several improvements on Bain's design and demonstrated

23405-404: Was still used, although it was accepted that poor weather ruled it out on many days of the year. France had an extensive optical telegraph system dating from Napoleonic times and was even slower to take up electrical systems. Eventually, electrostatic telegraphs were abandoned in favour of electromagnetic systems. An early experimental system ( Schilling , 1832) led to a proposal to establish

23560-479: Was the British Electric Telegraph Company (BETC), formed in 1849 by Henry Highton and his brother Edward. The ETC had a policy of suppressing competitors by buying up rival patents. This it had done to Highton when he patented a gold-leaf telegraph instrument. However, Highton now proposed a telegraph with a different system. Even worse for the ETC, in 1850 Parliament passed an Act giving it

23715-556: 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

23870-427: Was the first ship to be permanently fitted out as a cable ship and operated on a full-time basis by a cable company, although the fitting out for the Netherlands cables was considered temporary. She was a paddle steamer built in 1830 at Thornton-on-Tees with a 130 hp engine. She was the first of a series of cable ships named Monarch . The cable laying equipment of Monarch was a major step forward compared to

24025-473: Was used by British military in many colonial wars, including the Anglo-Zulu War (1879). At some point, a morse key was added to the apparatus to give the operator the same degree of control as in the electric telegraph. Another type of heliograph was the heliostat or heliotrope fitted with a Colomb shutter. The heliostat was essentially a surveying instrument with a fixed mirror and so could not transmit

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