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National Geographic : 1947 Mar
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The National Geographic Magazine Not long ago a man riding in an automobile in Washington, D. C., picked up a telephone on the dashboard and talked to his wife in England, learning, incidentally, that their grandson had had his first tooth. That was a demonstration of the new mobile radiotelephone service which is rapidly being put into use in large cities and on major high way routes in this country (Plate III). With this service you have in your car a telephone with its own number. If you are a salesman, for instance, out around town in your car, the boss may want to tell you right away about a new good pros pect for a sale. He merely calls your car telephone number, the call goes by wire to a radiotelephone station, then through the air to your car. A bell rings and a light flashes on your dashboard. You pick up the phone and carry on a conversation. Later, if you want to call the boss to tell him you put over the deal, you can call him direct from the car. If you're out on the road between New York and Philadelphia, the boss can get you by calling long distance, giving your car telephone number, and saying he thinks you're about 20 miles south of Newark. The toll operator routes the call through the radiotelephone station that is nearest to that locality. If you don't answer, she tries the next station on down the road. You can see this system's usefulness for salesmen, police, doctors, buses, newspapers, delivery trucks, and public utility repair crews. Telephoning to passengers or the engineer on a moving train also will be possible. Even tually, you may be able to talk this way from one train to another in different parts of the country or even of the world, and probably between passenger planes and the ground. Just delivering your voice anywhere you want it sent, over the existing maze of Ameri can telephone wires, is a big enough job. To transmit a human voice over the telephone, you need first to know how the voice works and what it can do, and to make it heard at the other end you need to know how the ear works and what it can and cannot hear. Alexander Graham Bell, in one of his early experiments, sang songs into a human ear obtained from a medical school. He attached a thin straw to the inner part of the ear, fixed so one end rested against a plate of smoked glass. When he sang into the ear, the sound waves set up by his voice vibrated the eardrum, and the straw made wavy lines on the smoked glass. In this way he obtained a picture of sound waves that helped in his invention of the telephone. You can still see those old glass plates with the wavy lines on them, preserved at the Bell Laboratories (page 281). Today Bell scientists are still experimenting with the human ear. Between 20 and 40 thou sand nerve fibers connect the ear to the brain. These nerves, telling the brain what the ear hears, form the last link in the process of transmitting the voice over the telephone. New knowledge of deafness and what to do about it also has come from these studies of the human ear. A device to measure the hear ing of a whole roomful of school children at once was developed by Bell scientists. The children listen to a series of numbers spoken with steadily diminishing loudness, and write them down as long as they can hear them. The last number written indicates the degree of the child's deafness, if any. These tests, now widely used in schools, have shown that one of every 15 American school children is handicapped in his school work by some degree of permanent or temporary deafness. One Person in 10 Is a Little Deaf The hearing of more than half a million peo ple was tested in the same way at the New York and San Francisco world's fairs of 1939-40, the first tests ever made of the hear ing of a large cross section of the population. Results showed that one in every 10 persons is deaf to some degree, but that some people have supernormal hearing. Speaking, of course, is just as important as hearing in the telephone system. It begins with the larynx, which contains the vocal cords. They really are not cords but two curtainlike membranes, in your throat behind your Adam's apple, that vibrate when you talk. Seeking to learn how the vocal cords work, to see if the telephone transmitter was prop erly designed to handle the sounds that the cords give out, Bell Laboratories scientists took the first high-speed movies ever made of the vocal cords in action (Plate II). People used to think that the cords vibrated like a banjo string, but the movies, run in slow motion, showed that they really have a sort of wavelike action, somewhat like clothes flapping on the line on a windy day. From the movies they learned, too, that sound comes from the vocal cords in puffs. Since the telephone was already designed to handle this type of energy properly, no changes were needed. The movies revealed that a person with a well-trained voice keeps his vocal cords closed until air pressure is built up in the chest and expelled strongly. In a person with an untrained voice the cords are open most of the time. 288
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