Specific Heat near the Critical Point

A theory is given for the specific heat of a simple fluid in the critical region in the homogeneous phase above Tc. The excess heat capacity is related to the long-wavelength contribution to the mean-square fluctuation of internal energy. The derivation is based on the assumption that the Planck function of a fluid system in thermal equilibrium in a nonuniform state above the critical point is an analytic functional of the density distribution. The result obtained agrees with the predictions of the scaling laws. A discussion of the relationships between our theory and some recently published works is also included.