on the theory of aether, a hypothetical substance that at that time was believed to fill all space. As a result of his research on November 29, 1903, De Pretto published a 62-page paper in the Atti del Reale Istituto Veneto di Scienze, Lettere ed Arti, vol LXIII (Proceedings of the Royal Veneto Institute of Science, Letters and Arts) entitled "Ipotesi dell'Etere nella Vita dell'Universo" ("Hypothesis of Aether in the Life of the Universe"). The paper was endorsed by the famous astronomer Giovanni Schiaparelli. De Pretto's paper was later included in the proceedings of an Italian scientific institute The Royal Veneto Institute of Science. This theory was similar to Samuel Tolver Preston's 1875 hypothesis that matter and energy might be interchangeable. De Pretto's theory was based on his hypothesis that a mass traveling at velocity v has the potential energy (forza viva) proportional to mv2 (the exact formula is mv2). In the section of his paper headed Energy of the Ether and Potential Energy in Matter, De Pretto wrote: Matter uses and stores energy as inertia, just like a steam engine that uses the energy in steam and stores energy in inertia as potential energy[... ] All components of a body are animated by infinitesimal but rapid movements equal to perhaps the vibration of the ether. It must be concluded that the matter in any body contains the sum of the energy represented by the entire mass of that body if it could move through space with the speed of a single particle. By theorizing "vibration of the ether", De Pretto asserted that mass is vibrating energy and that mass and energy are therefore interchangeable. He then speculated that ordinary matter may be considered to be vibrating at the speed of light c. According to De Pretto, The matter of any body contains within it a sum of energy represented by the entire mass of the body[... ] Nobody will easily admit that, stored in a latent state, in any kilogram of matter, completely hidden to all our investigations, hides such a sum of energy, equivalent to the amount that can be extracted from [burning] millions and millions of kilograms of coal." ½mv² versus mc² De Pretto used the expression for the "vis viva" and the energy store within matter, where he identified v with the speed of light. According to Italian mathematician Umberto Bartocci, his formula precedes by two