We study the influence of the gravitational field of Friedmann geometries upon an electromagnetic potential, through the Proca electromagnetic theory in a Dirac aether. The results are compared with those as foreseen by the Maxwellian theory in curved spacetime. Our findings show that strong amplification effects of electromagnetic fields are a distinctive possibility. Thence we discuss some related topics. * E-mail: alexandr@ov.ufrj.br 541 Mod. Phys. Lett. A 2001.16:541-555. Downloaded from www.worldscientific.com by NORTHEASTERN UNIVERSITY on 02/02/15. For personal use only.