Прочитайте текст и выберите утверждение соответствующее содержанию текста Real telegraphs were possi...: ответ на тест 438969 - Английский язык

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Real telegraphs were possible until it was proved that electricity and magnetism were connected. It was found that a needle of a compass moved when it was put near а wirе with a current flowing through it. A compass needle is a magnet. If a wire carrying a current could move it, then the wire must be a magnet too.

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Real telegraphs were possible until it was proved that electricity and magnetism were connected. It was found that a needle of a compass moved when it was put near а wirе with a current flowing through it. A compass needle is a magnet. If a wire carrying a current could move it, then the wire must be a magnet too.

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Only at the end of the 19th century electricity began to play its part in modern civilization. The man who achieved more in this field of practical engineering than any of his contemporaries was the American inventor, Thomas Alva Edison. He became interested in the problem of electric lighting. He knew what had been done in the field of electric lighting before his time, and he had seen some devices of his contemporaries, such as arc-lamp illuminations, which had been installed here and there. Two sticks of carbon, nearly touching, can be made to produce an electric arc which closes the circuit. Many scientists and inventors working in this field knew that only incandescent electric light - produced by some substance glowing in a vacuum so that it cannot burn up - could be used instead of gas lighting.

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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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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.

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For television fans who can’t make up their minds about which station to watch, a Taiwanese manufacturer has come up with a solution. The firm has introduced a three-screen television set. The unit features a 19-inch (47.5 cm), colour screen flanked on one side by a pair of 5-inch (12.5 cm), black-and-white screens mounted one above the other. Three channels can be watched at once, and using a remote control a viewer can rotate simultaneous broadcasts from one screen to another simply by pressing a button. One or both of the similar screens can also be hooked up to a closed-circuit camera, thus functioning as a security-surveillance monitor.