Abstract
The present paper contains an extension and generalization of results in a previous paper on the basis of the master equation for the approach to equilibrium of a system of interest. The concept of quasi-equilibrium of the system of interest associated with a time-dependent temperature is introduced and is then applied to a description of the processes of longitudinal and transverse relaxation in magnetic resonance and to a discussion of the law of entropy variation. Systems of interest of "size" comparable to their surroundings are consistently included in the treatment.