This paper reports on results taken to validate the extension to the theory of the magnetomechanical effect reported recently. This theory is based on a “law of approach” but the underlying equations have been generalized to include linear and nonlinear terms which are analogous to those in the well-known Rayleigh law of magnetization. It is shown that the generalized theory can be applied to materials with negative magnetostriction, such as nickel, and that the stress dependent model parameters can be determined from experimental measurements. It has been found that the results show improved agreement with experimental observation compared with the more restricted previous exposition of the model.