On the verification of the universality of free fall by neutron gravity refractometry

Koester's method of verifying the universality of free fall from a comparison of the values of neutron scattering lengths measured in the presence and absence of significant gravitational interaction is analyzed and a number of conceptual errors are corrected. These errors are, however, trivial in the sense that they affect only the justification of the method and not its validity. An analysis of recent scattering-length data is shown to confirm the universality of free fall within a relative uncertainty of 3×${10}^{-4\mathrm{}}$. The importance of Koester's method in providing a necessary complement to the more precise torsion-balance methods is pointed out.