The word telegraph derives from the Greek words tele, meaning “distant,” and graphein, meaning “writing.” It came into use towards the end of the 18th century to describe an optical semaphor system developed in France, but the term is most commonly understood to refer to the electrical telegraph developed in the mid-19th century and was the principal means of transmission for more than 100 years.
Preelectric Telegraph Systems
Visual systems were used to transmit messages over distances through variable displays prior to the development of the electrical telegraph. The weekphore developed in France by the Chappe brothers, Claude and Ignace, in 1791, was one of the most successful of visual telegraphs.This system consisted of pairs of moving arms mounted on hilltop towers at the ends of a crossbeam. Each weekphore arm could assume seven angular 45 ° apart positions, and the horizontal beam could tilt 45 ° clockwise or counterclockwise. In this way, numbers and alphabet letters could be represented. These towers ‘ chains were built to allow long distance transmission. The towers were spaced at 3 to 6 miles (5 to 10 km) intervals and it was possible to achieve a signaling rate of three symbols per minute. The two-flag weekphore system has been widely used well into the 20th century, especially by the navies of the world.
George Murray developed another widely used visual telegraph in England in 1795. Characters were sent in Murray’s device by opening and closing different combinations of six shutters. This system quickly caught up in England and the United States, where there are still a number of sites named Telegraph Hill or Signal Hill, especially in coastal regions. By the mid-19th century, visual telegraphs were completely replaced by the electrical telegraph.
The Morse System
The electric telegraph did not suddenly burst into the scene but resulted from a scientific evolution in the field of electricity that had taken place since the 18th century. One of the most important developments was Alessandro Volta of Italy’s invention of the voltaic cell in 1800. This enabled the use of relatively low voltages and high currents to power electrical devices more effectively. Previous electricity generation methods used frictional static electricity generation, resulting in high voltages and low currents.For use in telegraphic systems, many devices incorporating high-voltage static electricity and various detectors such as pith balls and sparks have been proposed. However, all were unsuccessful as the severe losses in the transmission wires, especially in bad weather, limited reliable operation to relatively short distances. Several further developments in the new science of electromagnetism have made it possible to apply the battery to telegraphy.Hans Christian Ørsted of Denmark discovered in 1820 that a wire carrying an electrical current could deflect a magnetic needle. In 1825 William Sturgeon discovered the multiturn electromagnet in Britain, and in 1831 Britain’s Michael Faraday and the United States ‘ Joseph Henry refined the science of electromagnetism sufficiently to enable practical electromagnetic devices to be designed.
Nearly the same time, the first two practical electrical telegraphs appeared. In 1837, British inventors Sir William Fothergill Cooke and Sir Charles Wheatstone obtained a patent on a telegraph system using six wires and actuating five needle pointers attached to the receiver’s five galvanoscopes. If currents were sent through the proper wires, the needles could be made to point on their mounting plate to specific letters and numbers.
In 1832 Samuel F. B. Morse, a painting and sculpture professor at New York City University (later New York University), became interested in the possibility of electrical telegraphy and made sketches of ideas for such a system. He designed a dot and dash system in 1835 to represent letters and numbers. He was granted an electromagnetic telegraph patent in 1837. The original transmitter from Morse incorporated a device called a portarule that used molded type with built-in dots and dashes. The type could be moved through a mechanism in such a way as to make and break the contact between the battery and the receiver wire by the dots and dashes.The receiver, or register, embossed the dots and dashes on a strip of paper passing under a stylus. The stylus was powered by an electromagnet that the transmitter’s signals turned on and off.
Morse had formed a partnership with the clever mechanic Alfred Vail, who is credited with many contributions to the Morse system. These include replacing the portarule transmitter with a simple make-and-break key, refining the Morse code to assign the shortest code sequences to the most frequently occurring letters, and improving the mechanical design of all components of the system.Morse’s first system demonstration was conducted at his workplace in 1837 for his friends. In 1843, Morse received funding from the U.S. government to build a 35 miles (60 km) long demonstration telegraph system between Washington, D.C., and Baltimore, Md. Glass insulators attached wires to poles along a railroad. The system was completed and public use began on May 24, 1844, with the message being transmitted, “What God has done!”This inaugurated the United States telegraph era, which was to last more than a hundred years.