ABSTRACT
The scaling theory includes the classical theory as a special case, but does not require the free energy to be analytic at the critical point. The units to use are appropriate combinations of the critical temperature, critical density, and critical pressure for a fluid and the analogous variables for magnetic systems. The scaling form has the additional feature that symmetries can be expressed simply in terms of the scaled, reduced variables. A very important task involved the critical evaluation of existing data on many different fluids and magnetic systems. This was needed to determine how the universal behavior is reflected in the thermodynamics of the critical point. It is one thing to postulate a form for the equation of state and the chemical potential in terms of scaled variables, and quite another thing to demonstrate that the form is useful over a significant range of the variables.
