The polarization produced in elastic scattering of 1.51 MeV neutrons from 18 medium-heavy and heavy nuclei has been measured at a scattering angle of 51.5°. The Li7(p, n)Be7 reaction was used at an angle of 35° as a source of 26% polarized neutrons. A pulsed beam time-of-flight system was employed and a neutron-gamma ray discrimination circuit was used in conjunction with an organic liquid scintillator for neutron detection. The observed polarizations are found to vary smoothly with atomic weight. Comparison of the experimental results is made with the predictions of a square-well complex potential model. To the extent that square-well calculations quite generally reproduce the major features of the predictions based on more sophisticated potentials, it is concluded that an additional term proportional to neutron excess, (N-Z) A, is required in the optical potential in order to fit the data for both medium-heavy and heavy nuclei.