Вопрос № 223256 - Английский язык

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Through the years other machines were invented, both to receive and transmit messages. These machines are called teleprinters. They use a code called the International 5-unit teleprinter code instead of the Morse code. It is called a "5-unit" code because a letter or a figure is made up of five impulses of electrical current, either positive or negative - three positive, two negative; one positive, four negative; and so on. All the letters are the same length in time. This is quite different from the Morse code, where E is the shortest and "nought" the longest.

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A lot of people began to see how electro-magnets could be used to send messages. One of the most famous people of all in communication is Samuel Morse. He invented the Morse code. This code is still used in signaling all over the world. His idea was simple. He thought of using time, sending current along a wire for a long time or a short time. Combining different sets of these “impulses”, just using the long or short, he made a code for the whole alphabet, and the numbers from 0 to 9.

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A teleprinter is really a machine which sends a typewriter message over a telegraph circuit. In fact, it looks like a typewriter and has the same keyboard. Every time one of the keys on the keyboard is pressed it sends the five impulses that make one letter or figure. It also sends a "start" impulse. This sets the teleprinter (or any number of them that are connected) at a receiving station ready to print the letter that follows immediately. A "stop" impulse brings all the teleprinters to rest after each letter or figure.

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In the early days of the telegraph and the telephone, men observed that signals sometimes jumped across the space between wires running next to each other, so that messages sent to one person went to another. They realized that electricity could pass through the air as well as along a wire. Just as sound travels through the air in waves, so electricity travels through the air in what we call radio waves. A. S. Popov, a Russian inventor, had the idea of sending messages by radio waves, or "by wireless". He constructed a coherer detector for the study of lightning discharges and his receiver was described in 1895.

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Radio was invented in Russia. The world's first receiver was constructed in 1895 by the great Russian scientist Alexander Popov. There were no transmitters then, therefore his receiver could only pick up signals produced by lightning discharges during a thunderstorm. A. Popov demonstrated a device called a "storm indicator" at a meeting of the Russian Physico-Chemical Society in St. Petersburg on May 7, 1895. This day is marked now as Radio Day. Soon Alexander Popov found a way of transmitting Morse code signals. In 1897 he sent the world's first wireless telegram over a distance of 600 m and four years later the range of transmission was increased to 150 km. Nowadays radio communication has no limits.

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The first television invention that had practical consequences was the “electrical telescope”, patented by Paul Nipkow in 1884. At the heart of his camera was the now famous Nipkow disk. It had 24 holes equally spaced along a spiral near the periphery of the disk. The image to be transmitted was focussed on a small region at the disk’s periphery, and the disk was made to spin at 600 revolutions per minute. As the disk rotated, the sequence of holes scanned the image in a straight line. A lens behind the image region collected the sequential light samples and focussed them on a single selenium cell. The cell would then produce a succession of currents, each proportional to the intensity of the light on a different element of the image.