ABSTRACT
This chapter presents a critical review of the state of knowledge about the constant of nature that relates the quantity of radiant heat and light to the temperature of the radiant object. Studies of this issue at the beginning of the 20th century ultimately led to the discovery of quantum mechanics, the keystone of modern physics. The continuity of this work at National Institute of Standards and Technology (NIST) for the remainder of the century also led to fundamental changes in the way that optical metrology is carried out. Samuel Wesley Stratton observed that a number of the national laboratories in Europe were expending considerable effort in measuring the radiation constants for describing the spectral distribution and total radiation from blackbody sources. The spectral distribution of blackbody radiation, that is, its radiance at different wavelengths, is determined by its temperature.
