2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/84094We show that for an observer in translational, rotational or gravitational motion, a linearly polarized plane wave has two modes of propagation in a stationary, homogeneous and isotropic medium according to Hertz's version of Maxwell's theory. The first mode is characterized by polarization at right angles to the direction of propagation and has a phase velocity that is controlled by the material constants of the medium. The second mode is characterized by polarization along the propagation direction and has a phase velocity that is controlled by the motion of the observer. We outline some applications of the second mode in emerging technologies.20 pages, minor corrections and clarificationsGeneral PhysicsClassical PhysicsOpticstext