Study of the time dependence of physical properties in the transformation range of glass is complicated by the "memory effect" and the inherent nonlinearity which are characteristic of structural relaxation. A multiparameter model of structural relaxation is presented that differs from earlier models in that it takes account of both these effects. The model fits avilable experimental data well; these data were obtained for the most part by observing the evolution of properties (such as density or refractive index) following a step change in temperature. This model also permits prediction of the physical properties of glass subjected to arbitrary and more complex temperture-time histories. It should, therefore, also be useful in the rational design of heat treating processes such as annealing.
