Portrait of the British physicist John Tyndall, 1820-1893. After starting a career in surveying and engineering Tyndall studied physical sciences at Marburg in Germany. He worked on thermal conductivity in gases. His studies of the scattering of light by fine particles in the air and in liquids resulted in the discovery of the Tyndall effect, whereby a beam of light is made visible by such scattering. He also realised why the sky is blue: atmospheric dust particles (and density differences in the air) scatter shorter wavelength (blue) components of sunlight more than the longer wavelength (red) components.