Abstract

The principle of conservation of energy tells us that ‘energy can neither be created nor destroyed but only transformed’. The validity of the principle is without question. The problem is the concept. Contemporary physicists have asserted that we do not know what energy is. We find, however, 19th century physicists, contemporary physicists and historians of science who converge on the point: Mayer and Joule discovered energy. Therefore, we do not know what energy is, but we know these authors discovered it. What did they then discover? What can we learn from this with regard to the energy concept problem? To deal with this issue, I will distinguish between what the authors did experimentally and what they said about the phenomena. This method of analysis makes the difference in relation to historical works on the subject. In a second step, I will consider the introduction of the energy concept, which is from 1850s, and the reification of the energy in 1880s. Finally, I will address the energy conservation principle and the concept of energy conveyed by this principle in contemporary textbooks. As we shall see, the conservation of a magnitude that we call energy nowadays was discovered by Mayer and Joule; an indestructible and transformable entity was not. Adopting the original conservation principle would be enough to avoid the energy concept problem.