SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Cups and string. Engraving of a man and woman using a simple telephone system comprised of two cups and a length of string. When one person speaks into a cup, the notes in the voice will cause pressure waves in the air. If the string is held taut, these pressure waves will be transmitted along the string to the other cup. Another person can then hear the first person's voice. Image from the 19th century.
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