ABSTRACT
The response of most materials to mechanical, electrical, optical and other force fields is time-dependent. The study of the responses to these force fields allows one to determine, respectively, the rheological, dielectrical and bire fringence properties of materials. According to the second law of thermo dynamics, part of the input energy involved in the perturbation must invariably be dissipated, and part of it is stored. It should be pointed out
that dissipation of energy does not occur instantaneously; it may take place in a time infinitely short, infinitely long, or finite, depending on the thermo dynamic state and nature of the material.
