  A non-minimal coupling of Weyl curvatures to electromagnetic fields is
considered in Brans-Dicke-Maxwell theory. The gravitational field equations are
formulated in a Riemannian spacetime where the spacetime torsion is constrained
to zero by the method of Lagrange multipliers in the language of exterior
differential forms. The significance and ramifications of non-minimal couplings
to gravity are examined in a pp-wave spacetime.
