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Loudspeaker apparatus, as constructed in the laboratory of the French physicist Henri Becquerel (1852-1908). This apparatus includes a Ruhmkorff coil (induction coil, top) and was constructed by Becquerel's demonstrator Peignot. It was intended for the amplification of voices in amphitheatres and lecture halls, and was known in French as a 'telephone a haute voix' (speaking aloud telephone). Artwork from the seventh volume (first period of 1891) of the French popular science weekly 'La Science Illustree'.
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