2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/116908The mass-energy relation E=mc2 has a dual origin, one grounded in the postulate of the existence of an aether made of "ultramondane particules" moving in space at the speed of light, c; the other, a consequence, first deduced by Henri Poincare, of John Poynting's electromagnetic Theorem.5 pagesGeneral Physicstext