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National Geographic : 1947 Sep
Contents
Split-second Time Runs Today's World standard frequencies broadcast by the Bu reau of Standards. In some types of radio receivers, quartz crystals vibrating at different frequencies separate the wave lengths of different sta tions, so you can tune to the one you wish to hear without interfer ence from the others. In the telephone sys tem, where many con versations travel to gether over the same wire or cable, each at its own frequency, crys tals vibrating at these different frequencies separate out the differ ent conversations on the receiving end so you hear only the one you want. Vibrations of those crystals are timed by standard fre quencies.* When a radio pro gramisputonana tional network, clocks in all the stations from coast to coast must agree, so that all will receive and send out the program exactly on the second. Shutters of some cameras are timed down to 1/1000 of a second or less. One high-speed camera used in photographing the human vocal cords in Rewound in Reverse, This Mainspring Will Increase in Strength After being coiled in one direction and heat-treated, mainsprings made of a new alloy used in Elgin watches (pages 414 and 428) are rewound in the oppo site direction on this machine, to improve their strength, or torque. The new alloy, containing eight different substances, is declared to be nonmagnetic and more resistant to stress than steel. action takes as many as 8,000 pictures in one second. X-ray pictures taken in one-millionth of a second are now possible, to reveal what is happening inside machines operating at very high speed. A ship captain, steering toward a strange coast after losing his bearings in the fog, sees a lighthouse flashing its beam at regular in tervals. Timing the flashes, he notes that they come, say, every five seconds, and that the beam revolves in 120. This tells him at once what light it is. Many lighthouses all over the world thus identify themselves with codes keyed to time. Radar sets depend on very accurate timing to show the distance of an object which the radar beam picks up. The fraction of a second it takes for the radar pulse to flash out and echo back from a ship, a plane, or an iceberg indicates how far away that object is. Measuring Millionths of a Second In war the range of guns can be set by radar. It takes only 1/10,000,000 of a second for a radar wave to travel to an object 50 feet * See, in the NATIONAL GEOGRAPHIC MAGAZINE, "Miracle of Talking by Telephone," October, 1937, and "Miracle Men of the Telephone," March, 1947, both by F. Barrows Colton; and "Prehistoric Tele phone Days," by Alexander Graham Bell, March, 1922. 403
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