  After an overview of various citations relevant in the context of photon
propagation, the relativistic Doppler effect and the addition theorem of
velocities are first derived taking into account momentum and energy
conservation. Clocks and the aberration of light are treated next, before the
lengths of rods and the Lorentz transformations are discussed. The
Michelson-Morley experiment is described at rest and in motion with respect to
a preferred aether system, first under the assumption of an operation in
vacuum. It is concluded that the aether concept is fully consistent with the
formal application of the Special Theory of Relativity (STR). Whether a
determination of the speed of the laboratory system relative to the aether is
possible, is considered next either for an operation of the experiment in
vacuum or in a medium with an index of refraction not equal to one. In both
cases, the answer appears to be negative.
