has always been important to mankind, and a lack of communication
in the past has resulted in terrible wars and tragedies. It could be said that
the reason that we have had world peace for so long is more to do with global
communications, than it has to do with diplomacy.
The Greek philosopher
Thales appears to have been the first to document the observations of electrical
force. For this he noted that on rubbing a piece of amber with fur caused it to
attracted feathers. It is interesting that the Greek name for amber was elektron
and the name has since been used in electrical engineering.
concept in electrical systems is that electrical energy is undoubtedly tied to
magnetic energy. Thus when there is an electric force, there is an associated
magnetic force. The growth in understanding of electrics and magnetics began during
the 1600s when the court physician of Queen Elizabeth I, William Gilbert, investigated
magnets and found that the Earth had a magnetic field. From this he found that
a freely suspended magnetic tends to align itself with the magnetic field lines
of the Earth. From then on, travelers around the world could easily plot their
course because they knew which way was North.
of the early research in magnetics and electrics was conducted in the Old World,
mainly in England, France and Germany. However, in 1752, Benjamin Franklin put
the USA on the scientific map when he flew a kite in an electrical storm and discovered
the flow of electrical current. This experiment is not recommended and resulted
in the untimely deaths of several scientists.
In 1785, the French scientist
Charles Coulomb showed that the force of attraction and repulsion of electrical
charges varied inversely with the square of the distance between them. He also
went on to show that two similar charges repel each other, while two dissimilar
Two scientists who would be commemorated by electrical
units made must of there major findings in the 1820s. The French scientist André
Ampère was studying electrical current in wires and the forces between
them, and then, in 1827, the German scientist Georg Ohm studied the resistance
to electrical flow. From this, he determined that resistance in a conductor was
equal to the voltage across the material divided by current through it. Soon after
this, English scientist Michael Faraday produced an electric generator when he
found that the motion of a wire through an electric field generated electricity.
From this, he mathematically expressed the link between magnetism and electricity.
root of modern communication can be traced back to the work of Henry, Maxwell,
Hertz, Bell, Marconi and Watt. American Joseph Henry produced the first electromagnet
when he wrapped a coil of insulated electrical wire around a metal inner. Henry,
un-fortunately, like many other great scientists, did not patent his discovery.
If he had he would have enjoyed his retirement years as a very wealthy man, rather
than on his poor pension. The first application of the electromagnet was in telegraphy,
which was the beginning of the communications industry. Henry sent coded electrical
pulses over telegraph wires to an electromagnet at the other end. It was a great
success, but it was left to the artist Samuel Morse (the American Leonardo, according
to one of his biographers) to take much of the credit. Morse, of-course developed
Morse Code, which is a code of dots and dashes. He used Henry's system and installed
it in a telegraph system from Washington to Baltimore. The first transmitted message
was "What hath God wrought." It received excellent publicity
and after eight years there were over 23000miles (37000km) of telegraph wires
in the USA. Several of the first companies to develop telegraph systems went on
to become very large corporations, such as the Mississippi Valley Printing Telegraph
Company which later be-came the Western Union. One of the first non-commercial
uses of telegraph was in the Crimean War and the American Civil War, where a communications
line from New York to San Francisco was an important mechanism for transmitting
information to and from troops.
important developers of telegraph systems around the world were P.L. Shilling
in Russia, Gauss and Weber in Germany, and Cooke and Wheatstone in Britain. In
1839 Cooke and Wheatstone opened telegraph system alongside the main railway route
running west from London.
One of the all time greats was the James
Clerk Maxwell, who was born in Edinburgh in 1831. He rates amongst the greatest
of all the human beings who have walked on this planet and his importance
to science puts him on par with Isaac Newton, Albert Einstein, James Watt and
Michael Faraday. Maxwell's most famous formulation was a set of four equations
that define the basic laws of electricity and magnetism (Maxwell's equations).
Before Maxwell's work, many scientists had observed the relationship between electricity
and magnetism. However, it was Maxwell, who finally derived the mathematical link
between these forces. His four short equations described exactly the behavior
and interaction of electric and magnetic fields. From this work, he also proved
that all electromagnetic waves, in a vacuum, travel at 300000 km per second (or
186000 miles per second). This, Maxwell recognized, was equal to the speed of
light and from this, he deduced that light was also an electromagnetic wave. He
then reasoned that the electromagnetic wave spectrum must contain many invisible
waves, each with its own wavelength and characteristic. Other practical scientists,
such as Hertz and Marconi soon discovered these 'unseen' waves. The electromagnetic
spectrum was soon filled with infrared waves, ultraviolet, gamma ray, X-rays and
radio waves (and some even proposed waves which did not even exist).
Maxwell is probably the second greatest scientist ever (Isaac
Newton would obviously be in first place). Maxwell's four equations which define
the propagation of every electromagnetic wave:
While Maxwell would provide a foundation for the transmission of electrical
signals, another Scot, Alexander Graham Bell, would provide a mechanism for the
transmission and reception of sound: the telephone. From his time in Scotland
he has always had a great in-terest in the study of speech and elocution. In the
USA, he fully developed his interest and opened the Boston School for the Deaf.
His other interest was in multiple telegraphy and he worked on a device which
he called a harmonic telegraph, which he used to aid the teaching of speech to
deaf people. In 1876, out of this research he produced the first telephone with
an electromagnet for the mouthpiece and the receiver. Alexander Graham Bell actually
made the telephone call to his assistant with the words "Mr Watson, come
here, I want you". Unlike many other great inventions it got good press
coverage. "It talks" was one of the headline (it has not stopped since).
Even the great Maxwell was even amazed that anything so simple could reproduce
the human voice and, in 1877, Queen Victoria acquired a telephone. Edison then
enhanced it by using carbon powder in the diaphragm, to create a basic microphone.
This produced an increased amount of electrical current. To fully commercial-ize
his invention, Bell along with several others formed the Bell Telephone Company
which fully developed the telephone so that, by 1915, long-distance telephone
calls were possible. Bell's patent number 174465 is the most lucrative ever issued.
At the time, a reporter wrote, about the telephone, "It is an interesting
toy . but it can never be of any practical value."
Around 1851, the
brothers Jacob and John Watkins Brett laid a cable across the English Channel
between Dover and Cape Griz Nez. It was the first use of electrical communica-tions
between England and France (unfortunately a French fisherman mistook it for a
sea monster and trawled it up). The British maintained a monopoly on submarine
cables and laid cables across the Thames, Scotland to Ireland, England to Holland,
as well as cables under the Black Sea, the Mississippi River and the Gulf of St
Lawrence. Submarine cables have since been placed under most of the major seas
and oceans around the world.
Around 1888, German Heinrich Hertz detected
radio waves (as predicted by Maxwell) when he found that a spark produced an electrical
current in a wire on the other side of the room. Then, Guglielmo Marconi, in 1896,
succeeded in transmitting radio waves over a dis-tance of two miles. From this
humble start, he soon managed to transmit a radio wave across the Atlantic Ocean.
Scot Robert Watson-Watt made RADAR (radio detection and ranging) practicable
in 1935, by transmitting microwave electromagnetic pulses which where reflected
by metal objects (normally planes or ships) and were detected by a receiver. Today
it is used in many applications from detect missiles and planes, to detecting
rain clouds and detecting the speed of motor cars. Microwave signals have been
important in the development of satellite communications.
of modern communications
The main developments of modern communications
Automated telephone switching. After the telephone's initial development,
call switching was achieved by using operators. This tended to limit the range
of the calls, and was particularly unreliable (and not very secure, as operators
would often listen to the tele-phone conversation). However, in 1889, Almon Strowger,
a Kansas City undertaker, patented an automatic switching system. In one of the
least catchy advertising slogans, it was advertised as "a girl-less, cuss-less,
out-of-orderless, wait-less telephone system". His motivation for the invention
was to prevent his calls being diverted to a business competitor by his local
operator. It used a pawl-and-ratchet system to move a wiper over a set of electrical
contacts. This led to the development of the Strowger exchange, which was used
extensively until the 1970s. Another important improvement came with the crossbar,
which allowed many inputs to connect to many outputs, simply by ad-dressing the
required connection. The first inventor is claimed to be J.N Reynolds of Bell
Systems, but it is normally given to G.A. Betulander.
Radio transmission. One of the few benefits of war (whether it be a
real war or a cold war) is the rapid development of science and technology. Radio
transmission benefited from this over World War I. A by-product of this work was
frequency modulation (FM) and amplitude modulation (AM). In these, signals to
be carried on (modulated) high frequency carrier waves which traveled through
the air better than unmodulated waves. Another by-product of the war effort was
frequency division multiplexing (FDM) which allowed many signals to be transmitted
over the same channel, but with a different car-rier frequency.
Trans-continental cables. After the Second World War, the first telephone
cable across the Atlantic was laid from Oban, in Scotland to Clarenville in Newfoundland.
Previ-ously, in 1902, the first Pacific Ocean cable was laid. A cable, laid in
1963, stretches from Australia to Canada. These trans-continental cables are now
important trunk routes for the global Internet. Their capacity has increased over
the years, especially with the in-troduction of fiber optic cables.
Satellites. The first artificial satellite was Sputnik 1, which was
launched by the USSR in 1957. This was closed followed in the following year by
the US satellite, Explorer 1. The great revolution can when the ATT-owned Telstar
satellite started communicating over large distances using microwave signals.
It used microwave signals which could propa-gate through rain and clouds and bounce
off the satellite. The amount of information that can be transmitted varies with
the bandwidth of the system, and is normally lim-ited by the transmission system.
A satellite system can carry as much as 10 times the amount of information that
a radio wave can carry. This allows several TV channels to be transmitted simultaneously
and/or thousands of telephone calls. Satellite TV sta-tions have been popular
in transmitting TV stations over large areas.
Digital transmission and coding. Most information transmitted is now
transmitted in the form of digital pulses. A standard code for this transmission,
called Pulse code modulation (PCM), was invented by A.H. Reeves in the 1930s,
but not used until the 1960s. A major problem in the past with computers systems
was that they used different codes to transmit text. To overcome this Baudot developed
a 5-unit standard code for telegraph systems. Unfortunately, it had a limited
alphabet of upper-case letters and had only a few punctuation symbols. In 1966,
ANSI defined a new standard code called ASCII. This has since become the standard
coding system for text-based communica-tions. It has only recently been upgraded
with Unicode (which uses 16 bits). In its standard form it uses 7 bits and can
thus only represent up to 128 characters. It has since been modified to support
an 8-bit code (called Extended ASCII).
Fiber optic transmissions. Satellite communications increased the amount
of data that could be transmitted over a channel, but in 1965 Charles Kao laid
down the future of high-capacity communication with the proof that data could
be carried using optical fibers. Optical fibers now provide the backbone to many
networks, including the Inter-net. Satellites supported the transmission of many
hundreds of bits per second, but fiber optics could support billions of bits per
second over a single fiber. They are reliable, and have excellent capacity for
future upgrading with a new transfer rate.
Chapter 7, Mastering Computing, W.Buchanan, Palgrave.
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