John Tyndall, Irish physicist, c 1890s .

IRELAND - SEPTEMBER 09: Photogravure after an original painting by Hamilton of the Irish physicist, John Tyndall (1820-1893), c 1890s. In the 1850s Tyndall began his pioneering studies on glacier formation, also becoming the first man to climb the Weisshorn in 1856. In 1859 he began his researches on heat radiation, followed by the acoustic properties of the atmosphere and the blue colour of the sky. His research resulted in the discovery of the 'Tyndall Effect', whereby a beam of light is made visible by the scattering of light by fine particles in the air and in liquids. A prolific writer on scientific subjects, he died from accidental poisoning with chloral. From a collection of portraits of scientists published by Photographische Gesellschaft, Berlin, c 1910. (Photo by SSPL/Getty Images)