  As generally known, the speed of propagation of light in solid state bodies
can be different from the speed of light in vacuum. That the mere presence of
electric or magnetic fields in the vacuum can suffice to influence the speed of
light, is a hypothesis under discussion, which is based on considerations of
Quantumelectrodynamics.
  For a verification of this hypothesis, an interference-experiment might be
performed, of which the planning is given in this article.
