  We discuss a scaling theory of the lattice response in the vicinity of a
finite-temperature critical end point. The thermal expansivity is shown to be
more singular than the specific heat such that the Gr\"uneisen ratio diverges
as the critical point is approached, except for its immediate vicinity. More
generally, we express the thermal expansivity in terms of a scaling function
which we explicitly evaluate for the two-dimensional Ising universality class.
Recent thermal expansivity measurements on the layered organic conductor
kappa-(BEDT-TTF)_2 X close to the Mott transition are well described by our
theory.
