  If all space is occupied by a linear bianisotropic material--whether
homogeneous or not--then the concurrent replacements of the permittivity and
the impermeability tensors by the negatives of their respective complex
conjugates and of the magnetoelectric tensors by their respective complex
conjugates (in the Boys-Post representation) imply the conjugation of both E
and H, in the absence of externally impressed sources. This conjugation
symmetry in linear electromagnetism has observable consequences when the linear
bianisotropic material occupies a bounded region.
