  We propose a transform method from a force curve obtained by a surface force
apparatus (SFA) to a density distribution of a liquid on a surface of the SFA
probe. (We emphasize that the transform method is a theory for the experiment.)
In the method, two-body potential between the SFA probe and the solvent sphere
is modeled as the soft attractive potential with rigid wall. The model
potential is more realistic compared with the rigid potential applied in our
earlier work. The introduction of the model potential is the improved point of
the present transform method. The transform method is derived based on the
statistical mechanics of a simple liquid where the simple liquid is an ensemble
of small spheres. To derive the transform method, Kirkwood superposition
approximation is used. It is found that the transformation can be done by a
sequential computation. It is considered that the solvation structure can be
obtained more precisely by using the improved transform method.
