National Geographic : 1951 Dec
771 National Bureau of Standards Electric Bulbs, Burning until They Fail, Measure Their Life Span Accurately Samples of all the millions of lamps purchased annually by the Federal Government are checked by the Bureau. Bulbs of 40 and 60 watts have an average life of 1,000 hours; 100-watters, about 750. Fluorescent lamps burn approximately 7,500 hours. Such tests benefit the public, since most manufacturers make their lamps to meet Government standards (page 765). time benefits, too, for almost everything made wavelength this may not happen, and by today, from fine watches to locomotives, is shifting to it a station may still get its mes put together with nuts, bolts, and screws, sages through. Henceforth it will be far easier for mechanics Worst trouble comes when spots form on in one country to find spare parts and make the sun and streams of atomic particles shoot repairs for a machine manufactured in an- out from them toward the earth, badly dis other (page 762). rupting the ionosphere. Then radio messages may have to be rerouted over new paths half Forecasting "Radio Weather" a world away. NBS radio scientists keep a constant and Predicting these radio troubles is part of the wary eye on the sun because things that hap- job of the Bureau's radio men. They call it pen there interfere directly with life on earth, forecasting "radio weather." They regularly especially with radio, predict, three months ahead, what is the best Ultraviolet light speeding in from the sun wavelength to use between any two points on electrifies, or ionizes, layers of air 50 to 250 earth at any time of day or night, in order to miles aloft, creating what we call the iono- get a message through instead of having it lost sphere. Shortwave radio travels around the in space. They also forecast, a few weeks earth in big bounces between the ground and or days in advance, the day-to-day changes these layers, making long-distance radio com- in radio weather. munication possible.* Airlines, steamship lines, radio communica But the ionosphere is temperamental. tion companies, press wireless services, and Radio messages sent on a certain wavelength broadcasters all use these predictions. may bounce merrily along between earth and Sunspots cooperated with our armed forces sky to their destination in the morning, then * See New Frontier in the Sky," by F. Barrows * See "New Frontier in the Sky," by F. Barrows suddenly shoot right off through the ionosphere Colton, NATIONAL GEOGRAPHIC MAGAZINE, September, into outer space in the afternoon. On another 1946.