A telegraph is any system that transmits encoded information by signal across a distance. Although the word telegraph is usually associated with sending messages by means of an electric current, it was used originally to describe a visual system for sending coded messages.
Until the telephone became a workable system, the telegraph was the standard means of communication between and within metropolitan areas in both Europe and the United States. Telephones did not make the telegraph obsolete but rather complemented its use for many decades.
Today, telegrams and telexes still use telegraphy (the sending of messages by telegraph) but are rapidly being replaced by facsimile (fax) transmissions through telephone lines. Satellite transmission and high-frequency radio bands are used for international telegraphy.
The earliest forms of sending messages over distances were probably both visual and auditory. Smoke signals by day and beacon fires by night were used by the ancient people of China, Egypt, and Greece. Drum-beats extended the range of the human voice and are known to have been used to send messages, as have reed pipes and the ram's horn.
Words to Know
Battery: A device for converting chemical energy into electrical energy.
Code: A system in which some group of symbols is used to represent words.
Electromagnet: A temporary magnet whose effect is caused by an electric current.
Semaphore: A signaling device that uses moving arms, human or mechanical, whose position indicates letters or numbers.
In 1791, French engineer Claude Chappe (1763–1805) and his brother Ignace (1760–1829) invented the semaphore. The semaphore is an optical telegraph system that can be used to relay messages from hilltop to hilltop. The Chappes built a series of two-arm towers between cities. Each tower was equipped with telescopes pointing in either direction and a cross at its top with extended arms that could assume seven easily seen angular positions. Together, they could signal all the letters of the French alphabet as well as some numbers. Their system was successful and soon was duplicated elsewhere in Europe. It was Claude Chappe who coined the word telegraph. He combined the Greek words tele meaning "distant" and graphien meaning "to write," to define it as "writing at a distance." The shortcomings of Chappe's system, however, were its dependence on good weather and its need for a large operating staff. Advances in electricity soon put this system out of business.
It was the invention of the battery—a source of electricity for a telegraph—by Italian physicist Alessandro Volta (1745–1827) in 1800 that made Chappe's system obsolete. The telegraph provided a means for sending messages across wires at the speed of light. Several researchers in different countries attempted to exploit the communications aspects of this discovery. The first successful device, however, was invented by two Englishmen, William Fothergill Cooke (1806–1879) and Charles Wheatstone (1802–1875). Cooke and Wheatstone designed a telegraph system in 1837 that used five needles to point to letters of the alphabet and numbers that were arranged on a panel. Their electric telegraph was immediately put to use on the British railway system.
The modern telegraph
Although Cooke and Wheatstone built the first successful telegraph, it was an American artist and inventor, Samuel F. B. Morse (1791–1872), who devised a telegraphic method that eventually was adopted worldwide. Morse made use of ideas and suggestions provided by other scientists and inventors, including those of American physicist Joseph Henry (1797–1878) and a young mechanic named Alfred Vail (1807–1859). His first public demonstration was made at Vail's shop in Morristown, New Jersey, in 1837.
The commercial success of Morse's invention was assured in 1843 when the U.S. government appropriated funds to build a pole line from Baltimore, Maryland, to Washington, D.C. On May 24,1844, Morse sent the first telegraphic message along that system: "What hath God wrought?" The system became popular very quickly at least partly because skilled operators discovered that they could "read" a message by simply listening to the sound of the telegraph's clicking.
Operation of the telegraph
Morse's telegraph consists essentially of a source of electricity (such as a battery), an electromagnet, and an electric switch known as the key. To send a message, the operator presses down on the key. As the key comes into contact with a metal plate beneath it, an electric circuit is completed. Electricity flows out of the telegraph, into external electrical wires, to waiting receivers in other parts of the world.
At the receiver's end of the system, current flows from external wires into the receiving telegraph system. The electrical current flows through the electromagnet, creating a magnetic field. The magnetic field causes the receiver's key to be attracted to the plate beneath it. As the key comes into contact with the plate, it makes a click sound. The message received consists, therefore, of a series of clicks.
The same clicks are produced when the sender transmits the message. Each time the key is pushed down onto the plate beneath it, it makes the same click. The sender can vary the sound of the click by holding the key down for a shorter or a longer period of time. The same kind of short and long clicks are then picked up at the receiver's end.
The Morse code. In order to use the system just described, Morse needed to have some kind of code in which short clicks (dots) and long clicks (dashes) could be used to represent letters and numbers. The code he developed is one of the most famous in the world. It consists of various combinations of dots and dashes representing letters, numbers, and symbols. For example, the combination - · represents the letter a; the combination - ··· represents the letter b; and the combination - - - - - represents the number zero.
The invention of the telegraph could in some ways be seen as the real beginning of our modern age. For the first time, it was possible for messages to be transmitted throughout the world. Almost coincidental with the telegraph's birth was the emergence of a new kind of journalism that depended on providing up-to-the-minute information. Reporting events as they occurred began to take precedence over a newspaper's traditional editorial role. In addition, corporations became larger and more far-flung, and nations became necessarily more interdependent. With the telegraph, information—in all its aspects and forms—began to assume the critical role it plays today.