  In this paper the Planck function is derived in the frequency domain using
the method of oscillators. It is also presented in the wavelength domain and in
the wave number domain. The latter is mainly used in spectroscopy for studying
absorption and emission by gases. Also the power law of Stephan and Boltzmann
is derived for these various domains. It is shown that this power law is
generally independent of the domain in which the Planck function is presented.
A formula for the filtered spectrum is also given and expressed in the sense of
the power law of Stefan and Boltzmann. Furthermore, based on Wien's
displacement relationship, it is argued that the wavelength at which the
maximum of the Planck function presented in the wavelength domain occurs
differs from that of the maxima of the other domains by a factor of 1.76. As
Planck determined his elementary quantum of action, eventually called the
Planck constant, and the Boltzmann constant using Wien's displacement
relationship formulated for the wavelength domain, it is shown that the values
of these fundamental constants are not affected by the choice of domain in
which the Planck function is presented. Finally, the origin of the Planck
constant is discussed.
