We think about the problem of changes and conservations for a long while
The idea of conservation has led to the search for noticeable, measurable equilibria in changes as a basic method of scientific research. Naturally, the evolution of this idea also produced theories which were later refuted or substantially modified by science.
Such a superseded scientific theory was the phlogiston theory proposed for the changes of masses in combustion, whose refutation and explanation suggested to Lavoisier the role of Oxygen in combustion. Another similar theory was the theory of the aether which was thought to serve as a medium for the propagation of electromagnetic waves. This theory was refuted only by modern electro-dynamics and Einstein’s theory of relativity.
In the 19th century Robert Mayer laid the basics of thermodynamics in the relations of motion and heat, Maxwell the conceptual-mathematical coordination of electrodynamics in the equilibrium equations of motion, electricity and magnetism, and in the early 20th century Einstein presented his mass-energy equilibrium equation.