This work is a further development of the theory that explains electrostatic attractions and repulsions by the molecular vibration of objects acting on one another through the liquid aether that fills the vacuum and the interatomic spaces of substances. The 2000-year-old problem of a mechanical explanation of the laws of electrostatics is answered by the behavior of coupled oscillators. The physical origin of the electric field is that of a to-and-fro motion of the aether. Light and radio waves are shown to be longitudinal waves consisting of to-and-fro motions of the aether along the direction of wave propagation, which makes them essentially electric waves. Corroboration with results from previous works leads to the conclusion that the complete nature of light and radio waves is that of electro-gravitational waves. The 100-year-old problems of the photoelectric effect and of the wave-particle duality are solved by uncovering the direct link between voltage and frequency of vibration, by a new interpretation of de Broglie equation, and by advancing the new theory of light propagation in channels.