Abstract
TELEPHONY by means of light is a particular case of wireless telephony. It differs from what is generally understood as wireless telephony in no essential respect. In both cases electromagnetic waves are used, but whereas in ordinary wireless the waves are very long, in the case of light they are very short. As a consequence, telephony by light is easily directed by means of lenses or mirrors, and constitutes a secret means of communication-a state of affairs not yet attained in what is popularly known as Marconi wireless transmission. At the same time, the use of light imposes definite limits on the possible range of light telephony. An uninterrupted straight line is essential between the sending and receiving stations, and the extreme range is therefore determined by the curvature of the earth and the altitudes of the stations.
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RANKINE, A. Telephoning by Light. Nature 104, 604–606 (1920). https://doi.org/10.1038/104604a0
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DOI: https://doi.org/10.1038/104604a0
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