John Tyndall (1820-1893), Irish physicist. Born in County Carlow, Ireland, Tyndall was a surveyor and engineer before studying physics and becoming a professor at the Royal Institution, London, England, in 1854. He was one of the first scientists to recognise the Earth's natural greenhouse effect and in 1869 he discovered the Tyndall Effect - the diffusion of light by large colloidal particles in a solution. He realised that the sky is blue because molecules in the air scatter the shorter blue wavelengths of sunlight more than the longer red wavelengths.