From the history of telegraph

1. Any system that can transmit encoded information by signal across a distance may be called a telegraph. The word was coined in about 1792 from the Greek words tele, “far,” and graphein, “to write,” but the principle is much older. The earliest forms of telegraphy were probably smoke, fire, and drum signals. By about 300 BC Greeks had devised a method of alphabetic signaling using large vases visible from a distance. Letters were signified according to the positions of vases in a grid of rows and columns. A similar system was used by medieval prisoners tapping signals between cells, using grids.

2. In the late 18th century optical telegraphs were invented by Claude Chappe in France and by George Murray in England. Called semaphores, they relayed messages from hilltop to hilltop with the aid of telescopes. Chappe's system used a vertical timber holding a movable crossbar with indicators at each end that could assume various configurations like a signalman with flags. Murray's system used a large tower-mounted box with six panels that opened and closed in different coded combinations.

3. Rapid development of telegraph systems came with the discovery that electric impulses could be used to transmit signals along a wire. Among the many electric systems devised was the needle telegraph. This was based on Hans Christian Oersted's discovery in 1819 that an electric current in a wire caused a magnetized needle next to the wire to deflect. The five-needle telegraph - patented by William Fothergill Cooke and Charles Wheatstone in London in 1837—utilized this principle with a panel imprinted with letters and numerals to which the five needles pointed singly or in pairs. It was widely used in Great Britain, especially for railroad signaling.

4. The development of the electromagnet about that time provided Samuel F.B. Morse with a way to transmit and receive electric signals. Together with Alfred Vail, his partner from 1837, Morse developed the simple operator key—something like a single typewriter key—which when depressed completed an electric circuit and sent an electric pulse to a distant receiver. This was originally a device that embossed a series of dots and dashes on a paper roll. About 1856 a sounding key was developed; skilled operators could listen to what the key “said” and write the messages directly. Telegraph systems quickly spread across Europe and the United States and soon resulted in mergers and associations such as the Western Union Telegraph Company in 1856.

5. With growing telegraph traffic, refinements were necessary. The duplex circuit, developed in Germany, made it possible for messages to travel simultaneously in opposite directions on the same line. Thomas Edison devised a quadruplex system in 1874 that permitted four messages to travel at once, two going in each direction. The most revolutionary system was invented by Jean-Maurice-Émile Baudot. His time-division multiplex, invented in 1872, consisted of a brush arm that traveled around a copper ring divided into equal sectors. In each sector there were five segments capable of receiving electric impulses and corresponding to a five-level code. As the brush arm moved in its circle, it picked up a code number from one sector and then the next and so on. As many messages as there were sectors could be sent simultaneously. The Baudot code is still used in some modern teletype machines.

6. By the end of the 19th century, the world was crisscrossed by telegraph lines, including numerous cables across the Atlantic Ocean. Some early telegraphs using keyboards and type wheels could produce tapes of printed messages, which were long used in stock-exchange tickers. In 1903 Donald Murray of England combined Baudot's time-division multiplex system and its five-level code with a system for punching tape devised by Wheatstone to produce a system that transmitted page-form telegrams.The invention of the telephone made a new range of technology available to telegraphy, particularly in the field of high-speed information transmission. Other significant developments in telegraphy include the use of microwave radio links to carry up to 1,800 channels in a single circuit. Satellite transmission is now widely used for international telegraphy, as are the high-frequency radio bands. Many modern telegraph terminals consist of tele-printers using the American Standard Code for Information Interchange (ASCII), a seven-pulse code capable of producing 128 alphabet, number, and control signals.

Notes:

grid - сетка

deflect - отклоняться

emboss - выбивать

refinement - усовершенствование

duplex – дуплексная (связь)

quadruplex – квадраплексный

time-division multiplex – временное уплотнение

stock-exchange tickers – телеграфный аппарат, автоматически печатающий на ленте последние биржевые новости

II. Read the text and answer the questions:

1. What system can be called a telegraph?

2. Who invented optical telegraphs?

3. What discovery contributed to the rapid development of telegraph systems in the 19thcentury?

4. What principle was used in the five-needle telegraph patented by W. Cooke and Ch. Wheatstone?

5. Whose code is still used in some modern teletype machines?

6. Who produced a system that transmitted page-form telegrams?

III. Explain the origin of the word “telegraph”.

IV. Find the information about the earliest telegraph systems used.

V. Describe how A. Vail and S. Morse's simple operator key worked.

VI. Name refinements that were necessary for the development of telegraph in the 19thcentury.

VII. In paragraph 5 find the place about Baudot system.

VIII. Which paragraph contains information about the significant developments used in telegraphy nowadays.

IX. Give the main points of the text in 5-6 sentences.

UNIT 4

Part A

Date: 2015-12-13; view: 535; Нарушение авторских прав