Electrical telegraph
From Wikipedia, the free encyclopedia
A printing electrical telegraph receiver, with transmitter key at bottom right
This electrical telegraph from G.Hasler (Bern) was used by Gotthard Railway Company
An electrical telegraph is a telegraph that uses electrical signals, usually conveyed via dedicated
telecommunication lines or radio.
The electrical telegraph, or more commonly just telegraph, superseded optical semaphore
telegraph systems, thus becoming the first form of electrical telecommunications. In a matter of
decades after their creation in the 1830s, electrical telegraph networks permitted people and
commerce to transmit messages across both continents and oceans almost instantly, with
widespread social and economic impacts.
Contents
1 History
o 1.1 Early work
o 1.2 First working systems
2 Commercial telegraphy
o 2.1 Cooke and Wheatstone system
o 2.2 Morse system
o 2.3 Telegraphic improvements
2.3.1 Teleprinters
2.3.2 Oceanic telegraph cables
3 End of the telegraph era
4 See also
5 References
6 Bibliography
7 Further reading
8 External links
History
Early work
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Smmering's electric telegraph in 1809
From early studies of electricity, electrical phenomena were known to travel with great speed,
and many experimenters worked on the application of electricity to communications at a
distance.
All the known effects of electricity - such as sparks, electrostatic attraction, chemical changes,
electric shocks, and later electromagnetism - were applied to the problems of detecting controlled
transmissions of electricity at various distances.
In 1753 an anonymous writer in the Scots Magazine suggested an electrostatic telegraph. Using
one wire for each letter of the alphabet, a message could be transmitted by connecting the wire
terminals in turn to an electrostatic machine, and observing the deflection of pith balls at the far
end.[1] Telegraphs employing electrostatic attraction were the basis of early experiments in
electrical telegraphy in Europe, but were abandoned as being impractical and were never
developed into a useful communication system[citation needed].
In 1774 Georges-Louis Le Sage realised an early electric telegraph. The telegraph had a separate
wire for each of the 26 letters of the alphabet and its range was only between two rooms of his
home.[2]
In 1800 Alessandro Volta invented the voltaic pile, allowing for a continuous current of
electricity for experimentation. This became a source of a low-voltage current that could be used
to produce more distinct effects, and which was far less limited than the momentary discharge of
an electrostatic machine, which with Leyden jars were the only previously known man-made
sources of electricity.
Another very early experiment in electrical telegraphy was an 'electrochemical telegraph' created
by the German physician, anatomist and inventor Samuel Thomas von Smmering in 1809,
based on an earlier, less robust design of 1804 by Spanish polymath and scientist Francisco Salva
Campillo.[3] Both their designs employed multiple wires (up to 35) to represent almost all Latin
letters and numerals. Thus, messages could be conveyed electrically up to a few kilometers (in
von Smmering's design), with each of the telegraph receiver's wires immersed in a separate
glass tube of acid. An electric current was sequentially applied by the sender through the various
wires representing each digit of a message; at the recipient's end the currents electrolysed the
acid in the tubes in sequence, releasing streams of hydrogen bubbles next to each associated
letter or numeral. The telegraph receiver's operator would watch the bubbles and could then
record the transmitted message.[3] This is in contrast to later telegraphs that used a single wire
(with ground return).
Hans Christian rsted discovered in 1820 that an electric current produces a magnetic field
which will deflect a compass needle. In the same year Johann Schweigger invented the
galvanometer, with a coil of wire around a compass, which could be used as a sensitive indicator
for an electric current. In 1821, Andr-Marie Ampre suggested that telegraphy could be done by
a system of galvanometers, with one wire per galvanometer to indicate each letter, and said he
had experimented successfully with such a system. In 1824, Peter Barlow said that such a system
only worked to a distance of about 200 feet (61 m), and so was impractical[citation needed].
In 1825 William Sturgeon invented the electromagnet, with a single winding of uninsulated wire
on a piece of varnished iron, which increased the magnetic force produced by electric current.
Joseph Henry improved it in 1828 by placing several windings of insulated wire around the bar,
creating a much more powerful electromagnet which could operate a telegraph through the high
resistance of long telegraph wires.[citation needed] During his tenure at The Albany Academy from
1826 to 1832, Henry first demonstrated the theory of the 'magnetic telegraph' by ringing a bell
through a mile of wire strung around the room.[4]
In 1835 Joseph Henry and Edward Davy invented the critical electrical relay. Davy's relay used a
magnetic needle which dipped into a mercury contact when an electric current passed through
the surrounding coil.[5] This allowed a weak current to switch a larger current to operate a
powerful local electromagnet over very long distances.[6][7] Davy demonstrated his telegraph
system in Regent's Park in 1837 and was granted a patent on 4 July 1838. He also developed an
electric relay.[8]
Revolving alphanumeric dial created by Francis Ronalds as part of his electric telegraph (1816)
First working systems
The first working telegraph was built by the English inventor Francis Ronalds in 1816 and used
static electricity.[9][10] At the family home on Hammersmith Mall, he set up a complete
subterranean system in a 175 yard long trench as well as an eight mile long overhead telegraph.
The lines were connected at both ends to revolving dials marked with the letters of the alphabet
and electrical impulses sent along the wire were used to transmit messages. Offering his
invention to the Admiralty in July 1816, it was rejected as wholly unnecessary.[11] His account
of the scheme and the possibilities of rapid global communication in Descriptions of an
Electrical Telegraph and of some other Electrical Apparatus[12] was the first published work on
electric telegraphy and even described the risk of signal retardation due to induction.[13] Elements
of Ronalds design were utilised in the subsequent commercialisation of the telegraph over 20
years later.[14]
Pavel Schilling, an early pioneer of electrical telegraphy
The telegraph invented by Baron Schilling von Canstatt in 1832 had a transmitting device which
consisted of a keyboard with 16 black-and-white keys. These served for switching the electric
current. The receiving instrument consisted of six galvanometers with magnetic needles,
suspended from silk threads. Both stations of Shilling's telegraph were connected by eight wires;
six were connected with the galvanometers, one served for the return current and one - for a
signal bell. When at the starting station the operator pressed a key, the corresponding pointer was
deflected at the receiving station. Different positions of black and white flags on different disks
gave combinations which corresponded to the letters or numbers. Pavel Shilling subsequently
improved its apparatus. He reduced the number of connecting wires from eight to two.
On 21 October 1832, Schilling managed a short-distance transmission of signals between two
telegraphs in different rooms of his apartment. In 1836 the British government attempted to buy
the design but Schilling instead accepted overtures from Nicholas I of Russia. Schilling's
telegraph was tested on a 5-kilometre-long (3.1 mi) experimental underground and underwater
cable, laid around the building of the main Admiralty in Saint Petersburg and was approved for a
telegraph between the imperial palace at Peterhof and the naval base at Kronstadt. However, the
project was cancelled following Schilling's death in 1837.[15] Schilling was also one of the first to
put into practice the idea of the binary system of signal transmission.
In 1833, Carl Friedrich Gauss, together with the physics professor Wilhelm Weber in Gttingen
installed a 1,200-metre-long (3,900 ft) wire above the town's roofs. Gauss combined the
Poggendorff-Schweigger multiplicator with his magnetometer to build a more sensitive device,
the galvanometer. To change the direction of the electric current, he constructed a commutator of
his own. As a result, he was able to make the distant needle move in the direction set by the
commutator on the other end of the line.
At first, they used the telegraph to coordinate time, but soon they developed other signals;
finally, their own alphabet. The alphabet was encoded in a binary code which was transmitted by
positive or negative voltage pulses which were generated by means of moving an induction coil
up and down over a permanent magnet and connecting the coil with the transmission wires by
means of the commutator. The page of Gauss' laboratory notebook containing both his code and
the first message transmitted, as well as a replica of the telegraph made in the 1850s under the
instructions of Weber are kept in the faculty of physics at the University of Gttingen, in
Germany.
Gauss was convinced that this communication would be a help to his kingdom's towns. Later in
the same year, instead of a Voltaic pile, Gauss used an induction pulse, enabling him to transmit
seven letters a minute instead of two. The inventors and university were too poor to develop the
telegraph on their own, but they received funding from Alexander von Humboldt. Carl August
Steinheil in Munich was able to build a telegraph network within the city in 1835-6. He installed
a telegraph line along the first German railroad in 1835.
In 1836 an American scientist, Dr. David Alter, invented the first known American electric
telegraph, in Elderton, Pennsylvania, one year before the Morse telegraph. Alter demonstrated it
to witnesses but never developed the idea into a practical system.[16] When Alter was interviewed
for the book Biographical and Historical Cyclopedia of Indiana and Armstrong Counties, he said:
"I may say that there is no connection at all between the telegraph of Morse and others and that
of myself.... Professor Morse most probably never heard of me or my Elderton telegraph."
A Morse key (ca. 1900)
Samuel Morse independently developed and patented a recording electric telegraph in 1837.
Morse's assistant Alfred Vail developed an instrument that was called the register for recording
the received messages. It embossed dots and dashes on a moving paper tape by a stylus which
was operated by an electromagnet.[17] Morse and Vail developed the Morse code signalling
alphabet. The first telegram in the United States was sent by Morse on 11 January 1838, across
two miles (3 km) of wire at Speedwell Ironworks near Morristown, New Jersey, although it was
only later, in 1844, that he sent the message "WHAT HATH GOD WROUGHT?" over the 44
miles (71 km) from the Capitol in Washington to the old Mt. Clare Depot in Baltimore.[18][19]
Commercial telegraphy
Cooke and Wheatstone system
Cooke and Wheatstone's five-needle, six-wire telegraph
The first commercial electrical telegraph, the Cooke and Wheatstone telegraph, was co-
developed by William Fothergill Cooke and Charles Wheatstone. In May 1837 they patented a
telegraph system which used a number of needles on a board that could be moved to point to
letters of the alphabet. The patent recommended a five-needle system, but any number of needles
could be used depending on the number of characters it was required to code. A four-needle
system was installed between Euston and Camden Town in London on a rail line being
constructed by Robert Stephenson between London and Birmingham. It was successfully
demonstrated on 25 July 1837.[20] Euston needed to signal to an engine house at Camden Town
to start hauling the locomotive up the incline. As at Liverpool, the electric telegraph was in the
end rejected in favour of a pneumatic system with whistles.[21]
Cooke and Wheatstone had their first commercial success with a system installed on the Great
Western Railway over the 13 miles (21 km) from Paddington station to West Drayton in 1838,
the first commercial telegraph in the world.[22] This was a five-needle, six-wire[21] system. The
cables were originally installed underground in a steel conduit. However, the cables soon began
to fail as a result of deteriorating insulation and were replaced with uninsulated wires on
poles.[23] As an interim measure, a two-needle system was used with three of the remaining
working underground wires, which despite using only two needles had a greater number of
codes.[24] But when the line was extended to Slough in 1843, a one-needle, two-wire system was
installed.[25]
From this point the use of the electric telegraph started to grow on the new railways being built
from London. The London and Blackwall Railway (another rope-hauled application) was
equipped with the Cooke and Wheatstone telegraph when it opened in 1840, and many others
followed.[26] The one-needle telegraph proved highly successful on British railways, and 15,000
sets were still in use at the end of the nineteenth century. Some remained in service in the
1930s.[27] In September 1845 the financier John Lewis Ricardo and Cooke formed the Electric
Telegraph Company, the first public telegraphy company in the world. This company bought out
the Cooke and Wheatstone patents and solidly established the telegraph business.[28][29]
Morse system
In the United States, the Morse/Vail telegraph was quickly deployed in the two decades
following the first demonstration. The overland telegraph connected the west coast of the
continent to the east coast by 24 October 1861, bringing an end to the Pony Express.[30]
As well as the rapid expansion of the use of the telegraphs along the railways, they soon spread
into the field of mass communication with the instruments being installed in post offices. The era
of mass personal communication had begun.
Telegraphic improvements
Wheatstone automated telegraph network equipment
A continuing goal in telegraphy was to reduce the cost per message by reducing hand-work, or
increasing the sending rate.[citation needed] There were many experiments with moving pointers, and
various electrical encodings. However, most systems were too complicated and unreliable. A
successful expedient to reduce the cost per message was the development of telegraphese.
The first system that didn't require skilled technicians to operate, was Charles Wheatstone's ABC
system in 1840 where the letters of the alphabet were arranged around a clock-face, and the
signal caused a needle to indicate the letter. This early system required the receiver to be present
in real time to record the message and it reached speeds of up to 15 words a minute.
In 1846, Alexander Bain patented a chemical telegraph in Edinburgh. The signal current moved
an iron pen across a moving paper tape soaked in a mixture of ammonium nitrate and potassium
ferrocyanide, decomposing the chemical and producing readable blue marks in Morse code. The
speed of the printing telegraph was 1000 words per minute, but messages still required
translation into English by live copyists. Chemical telegraphy came to an end in the US in 1851,
when the Morse group defeated the Bain patent in the US District Court.[31]
For a brief period, starting with the New York-Boston line in 1848, some telegraph networks
began to employ sound operators, who were trained to understand Morse code aurally.
Gradually, the use of sound operators eliminated the need for telegraph receivers to include
register and tape. Instead, the receiving instrument was developed into a "sounder," an
electromagnet that was energized by a current and attracted a small iron lever. When the
sounding key was opened or closed, the sounder lever struck an anvil. The Morse operator
distinguished a dot and a dash by the short or long interval between the two clicks. The message
was then written out in long-hand.[32]
Royal Earl House developed and patented a letter-printing telegraph system in 1846 which
employed an alphabetic keyboard for the transmitter and automatically printed the letters on
paper at the receiver,[33] and followed this up with a steam-powered version in 1852.[34]
Advocates of printing telegraphy said it would eliminate Morse operators' errors. The House
machine was used on four main American telegraph lines by 1852. The speed of the House
machine was announced as 2600 words an hour.[35]
A Baudot keyboard, 1884
David Edward Hughes invented the printing telegraph in 1855; it used a keyboard of 26 keys for
the alphabet and a spinning type wheel that determined the letter being transmitted by the length
of time that had elapsed since the previous transmission. The system allowed for automatic
recording on the receiving end. The system was very stable and accurate and became the
accepted around the world.[36]
The next improvement was the Baudot code of 1874. French engineer mile Baudot patented a
printing telegraph in which the signals were translated automatically into typographic characters.
Each character was assigned a five-bit code, mechanically interpreted from the state of five
on/off switches. Operators had to maintain a steady rhythm, and the usual speed of operation was
30 words per minute.[37]
By this point reception had been automated, but the speed and accuracy of the transmission was
still limited to the skill of the human operator. The first practical automated system was patented
by Charles Wheatstone, the original inventor of the telegraph. The message (in Morse code) was
typed onto a piece of perforated tape using a keyboard-like device called the 'Stick Punch'. The
transmitter automatically ran the tape through and transmitted the message at the then
exceptionally high speed of 70 words per minute.
