Temperature of the Sun through the 19th century

Estimates for the surface temperature of the Sun through the 19th century, derived from measurements of the solar radiation on Earth. Different colors are used for the adopted relations between the radiation and the temperature of the radiating body. Stefan's law (P~T^4) was adopted in 1879 and theoretically justified by Boltzmann in 1884. See 'A popular history of astronomy during the 19th century', Agnes M. Clerke, 4th edition, 1908, for full references.