The Radiation Scale of Temperature between 175 °C and 1063 °C

Comparative measurements of monochromatic black-body radiation in the infra-red (2 to 4 μm) over temperature ranges between 175 °C and 1063 °C have been made. Temperatures were measured on the International Practical Scale, and the differences between the thermodynamic and practical scales determined. Assuming a value of 419.58 °C for the freezing point of zinc, in conformity with recent gas thermometry, and a value of 0.014 388 m.deg for the constant c 2 in Planck's equation, agreement with gas thermometry is good up to 780 °C, but thereafter temperatures measured on the radiation scale are lower. Recent gas thermometer values for the gold point range from 1063.7 °C to 1064.5 °C, with a mean of 1064.2 °C, while the radiation measurements give 1063.7 °C, with limits of ± 0.6 deg calculated from the random errors. It is not thought that systematic errors add seriously to the uncertainty.