Liquid phase

The critical point

Gas phase

Kuhn’s Historiographic Interpretation:

Boltzmann’s work

Planck’s Black Body law

Einstein’s paper on quanta

A “phase transition” of the idea of a number of discrete cells; it originates in the framework of the continuum and then it is applied to a discrete reality

Boltzmann’s partition of the continuum in a number of finite cells

Boltzmann’s finitistic idea is used by Planck, being unaware of the new physical reality

Einstein’s evidence for quanta