July 24th
1843 William de Wiveleslie Abney was born. He investigated colour photography and colour vision; pioneered a method to measure the relative proportions of the primaries in a sample colour; first to take infra-red photographs, and study the solar infra-red spectrum; introduced hydroquinone (1880) as an effective photograph developing chemical; measured infra-red spectra of organic compounds (1885); studied how sunlight is altered in passing through the atmosphere and invented the abney level.