The spectral emissivity of iron and cobalt has been determined as a function of the temperature. Sharp, definite changes in the emissivity have been observed in iron at the $A_3$ and $A_4$ point and at the Curie temperature for cobalt. A gradual change takes place in cobalt in the region where, presumably, the cobalt structure changes from hexagonal to cubic. A decrease in the neighborhood of 1370°K has been observed for iron.

• Received 2 June 1948

DOI:https://doi.org/10.1103/PhysRev.74.687