Tyndall's ratio spectrophotometer. 19th-century diagram of the apparatus used in 1860 by British physicist John Tyndall (1820-1893) to measure the ability of gases such as nitrogen, oxygen, water vapour, carbon dioxide, ozone, and methane to absorb radiant heat. The gas being tested was in the long tube, with a thermopile (centre left) and galvanometer (lower centre) used to measure temperature difference. This was a key development in early climate science. Tyndall was a professor at the Royal Institution, London. Diagram published in Tyndall's 'Contributions to Molecular Physics in the Domain of Radiant Heat' (1872).