Tyndall, John (1820–1893)

Irish physicist who 1869 studied the scattering of light by invisibly small suspended particles in colloids. Known as the Tyndall effect, it was first observed with colloidal solutions, in which a beam of light is made visible when it is scattered by minute colloidal particles (whereas a pure solvent does not scatter light). Similar scattering of blue wavelengths of sunlight by particles in the atmosphere makes the sky look blue (beyond the atmosphere, the sky is black).

Tyndall was born in County Carlow and studied at Marburg, Germany. He became professor at the Royal Institution 1853 and was also professor at the Royal School of Mines 1859–68. As superintendent of the Royal Institution from 1867, he did much to popularize science in Britain and also in the USA, where he toured from 1872 to 1873.

Having established that there are dust particles suspended in the air, Tyndall was able to show that the air contains living micro-organisms. This confirmed the work of French chemist Louis Pasteur that rejected the spontaneous generation of life, and it also inspired Tyndall to develop methods of sterilizing by heat treatment.

Tyndall also carried out experimental work on the absorption and transmission of heat by gases, especially water vapour and atmospheric gases, which was important in the development of meteorology.