  The influence of the gravity acceleration on the regularized energy-momentum
tensor of the quantized electromagnetic field between two plane parallel
conducting plates is derived. We use Fermi coordinates and work to first order
in the constant acceleration parameter. A perturbative expansion, to this
order, of the Green functions involved and of the energy-momentum tensor is
derived by means of the covariant geodesic point splitting procedure. In
correspondence to the Green functions satisfying mixed and gauge-invariant
boundary conditions, and Ward identities, the energy-momentum tensor is
covariantly conserved and satisfies the expected relation between
gauge-breaking and ghost parts. A more systematic derivation is therefore
obtained of the theoretical prediction according to which the Casimir device in
a weak gravitational field will experience a tiny push in the upwards
direction.
