John Tyndall. Engraving of John Tyndall (1820-93), giving an electricity lecture at the Royal Instit- ution in London, Britain, in 1870. He was a sur-

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John Tyndall. Engraving of John Tyndall (1820-93), giving an electricity lecture at the Royal Instit- ution in London, Britain, in 1870. He was a sur- veyor & engineer before studying physics & becom- ing a professor at the Royal Institution in 1854. He was 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 shorter wavelength (blue) components of sunlight more than the longer wavelength (red) components.

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Keywords: blue, effect, electricity, historical, history, john, lecture, light, physics, pioneer, portraits, proposer, scattering, sky, surname, tyndall