  We point out that current textbooks of modern physics are a century
out-of-date in their treatment of blackbody radiation within classical physics.
Relativistic classical electrodynamics including classical electromagnetic
zero-point radiation gives the Planck spectrum with zero-point radiation as the
blackbody radiation spectrum. In contrast, nonrelativistic mechanics cannot
support the idea of zero-point energy; therefore if nonrelativistic classical
statistical mechanics or nonrelativistic mechanical scatterers are invoked for
radiation equilibrium, one arrives at only the low-frequency Rayleigh-Jeans
part of the spectrum which involves no zero-point energy, and does not include
the high-frequency part of the spectrum involving relativistically-invariant
classical zero-point radiation. Here we first discuss the correct understanding
of blackbody radiation within relativistic classical physics, and then we
review the historical treatment. Finally, we point out how the presence of
Lorentz-invariant classical zero-point radiation and the use of relativistic
particle interactions transform the previous historical arguments so as now to
give the Planck spectrum including classical zero-point radiation. Within
relativistic classical electromagnetic theory, Planck's constant h appears as
the scale of source-free zero-point radiation.
