Short Wave Radio Echoes


    IT is now well-known that all long-distance radio communication takes place by means of electric waves reflected from one of the ionised regions of the atmosphere, the time of travel of the waves from the emitting station up to the reflecting layer and back to the earth being usually a small fraction of a second. Some six years ago, a Norwegian engineer, G. Hals, discovered the existence at certain times on short wave-lengths of wireless echoes received as long as three seconds after the cessation of the original signals (see NATURE, 122, 681, Nov. 3, 1928). These observations were afterwards confirmed by Prof. C. Stormer, and specially organised experiments by experts in different countries showed that echoes of up to 25 or 30 seconds' delay could be detected, although they were of rather rare and uncertain occurrence.

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