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John Tyndall (1820-1893), Irish physicist. Tyndall was a surveyor and engineer before studying physics and becoming a professor at the Royal Institution, London, in 1854. A prolific writer on a number of subjects, he studied light beams passing through various substances. In 1869 he discovered the Tyndall Effect in which light scattering by colloidal particles in a solution makes the light beam visible from the side. He realised that the sky is blue because dust particles in the air scatter blue wavelengths more than red wavelengths. Artwork from the 13th volume (first period of 1894) of the French popular science weekly 'La Science Illustree'.
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