Radio age (Jan 1927-Jan 1928)

RADIO AGE /or January, 1927 The Magazine of the Hoar 61 Speed of Light Is Now Accurately Determined AT THE meeting of the National Academy of Sciences, at Philadelphia, November 8, Professor Albert A. Michelson, recognized dean of American physicists and professor at the University of Chicago, announced the most accurate figure ever obtained for the speed of light through space or in a vacuum. The figure previously accepted by scientists for this speed was 186,326 miles per second. As the result of a three-year investigation carried out on top of two mountains in California, Professor Michelson has corrected this figure slightly. The new figure for the speed of light is 186,284 miles per second. The final measurement of this value was accomplished by means of a rapidly-revolving sixteensided block having mirrors on each of its sixteen sides. A ray of light from a powerful arc lamp was focused on this revolving mirror-sided block, so that the succession of light flashes reflected as each mirror passed by was sent out of the laboratory on Mount Wilson and off toward another mountain top twenty-two miles away. On this other mountain top was a stationary mirror which reflected these light flashes back again to their original sources. While the light was on its journey to the distant mountain-top and return, the revolving set of mirrors at the source moved slightly, due to the rotation of the mirror-sided block. Accordingly the light flash returning from the distant mountain was not received on the same mirrorface from which it departed, but on the next face; this next face having been brought into line by the rotation of the mirror-faced block. The speed of rotation of this block could be altered by means of a throttle controlling the compressed air turbine which drove the block. By adjusting this speed so that the second mirror-face came to occupy for the returning light ray exactly the same position that the preceding mirror-face had occupied when the ray departed, it was possible for Professor Michelson to calculate the length of time (a little less than one four-thousandths of a second) that the light-flash had been on the way to the distant mountain-top and return. In order to make this calculation, the speed of rotation of the mirrorfaced block was measured accurately. Also, the United States Government engineers carried out a special and extremely accurate survey to determine the exact distance between the laboratory on Mount Wilson and the distant mirror. TO the layman, and even to some scientists, it may seem remarkable that so much labor and money should be expended on a single scientific experiment, especially when the only result expected from that experiment was the attaining of a slightly greater precision for a figure already known with a considerable accuracy. That the experiment was considered worth doing and important is due to the fact that the speed of light in space is felt by physicists to be the most fundamental of all of the constants of nature. This speed enters importantly into the calculations of the Einstein theory as well as into practically all modern theories of the nature of matter, of energy and of the universe. DEPENDABLE RADIO EQUIPMENT TRANSMITTING APPARATUS A Complete Stock at "CHIRAD" IN addition to our regular broadcast apparatus we carry a very good stock of transformers, chokes, grid leaks, high test condensers, etc., for transmitting purposes. 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