The Development of the Theory of Conduction of Heat

Abstract

Fourier’s theory of the conduction of heat may be characterized as an ideal physical theory. It is founded, not upon a hypothesis but upon an observable fact according to which the velocity of equalization of small differences of temperature is proportional to these differences themselves. Such a fact can be more precisely established or corrected by finer observations; but it can, as such, enter neither directly nor in its correct mathematical deductions into conflict with other facts. This foundation of the theory, with the entire structure supported by it, remains secure — while a hypothesis like that of the kinetic theory of gases, for example, which assumes molecules with evanescent reciprocal action and moved with great velocities in all directions, must be prepared at any moment for contradiction by new facts, no matter how much it may have contributed to the survey of the properties of gases up to that time.