The Telegraph and Beyond - pages 1 & 2
(Located at http://library.advanced.org/27887/gather/history/telegraphy.shtml)
Telegraphy is the first and most important system of long distance communication. It has been utilized for ages and is still used today. There are different kinds of telegraphspre-electric and electric telegraphy.
Telegraphy (derives from the Greek tele, "far", graphein, "to write") is a branch of telecommunications that consists in the sequential transmission of messages or dispatches by signs (alphabetic letters, numerals, punctuation, or symbols) or sounds. The telegraph is a department of telegraphy; it is a system of electric telegraphy. It is a communication system that requires electrical instruments to transfer, or transmit, and receive signals, or coded messages, through electrical pulses.
This type of telegraphy refers to the long distance communication system used during the ancient days, when electricity did not exist. It can divide itself into three subcategories: non-literal, literal and visual telegraphy.
Non-literal telegraphy is a pattern that involves transmitting non-alphabetic messages at an extensive distance. As we remember back in the pre-historic era, man was unfamiliarized with words and was incapable of speaking. The only known means of communication that could be produced were sounds or gestures. Just as we, in the present age, use gestures or body signals to tell others what we want or express to others our feelings, back then, man also employed them. Another method of producing sounds was by beating objects. Pre-historic man learned to beat on resounding tree trunks or any piece of wood with a stick, like a drum, creating rhythmic sequential sounds.
Other non-literal communication systems that were used in ancient times were smoke and fire signals. Ancient people of Egypt, China, Greece, and Assyria practiced fire signalling by night and smoke signaling by day to establish sight of locations.
This type of pre-electric telegraphy requires alphabetic signaling. By 300 BC, a method of signaling the 24 letter Greek alphabet was invented. This technique consisted of placing alphabet letters in five rows and five columns on an iron frame in a way that the first letter of the alphabet, alpha, lies on the first row on the first column; and in a way that the last letter of the alphabet, omega, lies on the last row of the fourth column. All that was required was ten vases and two low walls in a row separated from one another by a few feet. The wall on the left represented the row; the wall on the right, the column. For example, to signal alpha, one vase was placed in front of the left wall, while another vase, in the front of the right. To signal omega, five vases were placed in front of the right wall; four vases were placed in front of the right one. Medieval prisoners practiced this same system of communication.
Another system of telegraphy was created optical telegraphy. A Frenchman, Claude Chappe, and an Englishman, George Murray, invented optical instruments and semaphores. These apparatus consisted in the transmission of messages from "hilltop to hilltop" with the help of a telescope. Chappe invented a system that used a "vertical beam holding a movable crossbar with indicators at each end that could assume various configurations". The second instrument, Murrays apparatus, was composed of "a large tower-mounted box with six panels that opened and closed in different combinations according to a code".
During the beginnings of the 19th century a modernized version of telegraphy emerged the electric telegraphy. It involved the employment of electricity. This type of telegraphy can divide itself into two groups: wire and wireless telegraphy.
This branch of telegraphy involves electric impulses that transmitted signals in a wire. One of the firsts discoveries made was the one of Hans Christian Orsted in 1819. It was based on electric current causing a magnetic needle or pointer to turn. Another discovery similar to Hans was later made in 1837. It was known as "Cooke and Wheatstones five needle telegraph", which utilized a panel, which was inscribed with letters and numbers.
Telegraphy systems were improving notably throughout the 20th century. In these systems wires were substituted for the use of microwave radio links, which carry up to 1,800 channels in a single circuit. This extensive development was due to business and government demands for machines that were easier to use. As a result, radiotelegraph companies expanded their bandwidth offerings. These improved developments included: microwave radio, waveguides, satellites, and lasers.
For international telegraphy, satellite transmissions were employed for their high-frequency radio bands. Nowadays, some teleprinters can print entire lines simultaneously at a rate of up to 1,000 per minute. Digital computers are also highly used for coding and decoding the transmission of signals at very high speeds.
As we can see, modern telegraphy offered society systems of communication with greater speed, efficiency, and more flexibility than those of the 19th century.
The Invention of the Telegraph
Morse and his partner, Alfred Vail, invented the "operator key" (like a single typewriter key). By depressing the operator key, a signal would be sent to a distant receiver. This key projected a series of dots and dashes on a paper roll. However, in 1856 everything changed.
A sounding key was developed as shown in figure 1-1. This apparatus allowed operators to listen to what the key "said" and typed the messages directly, after 1878. As the spread of telegraph systems increased, many associations in the United States and Europe, such as the Western Union Telegraph Company, were establishing (1856).
Later, in Germany, a duplex circuit was created, which made it possible for messages to travel at the same time, in opposite directions on the same line; after that, a quadruplex circuit was invented which permitted four messages to travel at once.
The most revolutionary discovery was Jean-Maurice-Emile Baudots "time division multiplex", in 1872. Her instrument contained a copper ring that was divided into equal sectors and a brush would travel around it to pick up coded numbers from each sector. The more sectors an apparatus had, the more messages that could be sent simultaneously.
"The world was crisscrossed by telegraph lines by the end of the XIX century " Between 1924 and 1928, teleprinters (transmitted page form telegrams) were developed and used for business communications. In 1933, these instruments were capable of printing only up to 500 characters per minute; by 1964 improved versions produced up to 900 characters per minute.