A Study of the behaviour of a glass as a function of the temperature shows the existence of a zone of temperature, below the softening point, where the structure of the glass varies. For every temperature of this "region of transformation" there exists an exact state of the glass which i not attained instantly. A study of the speed with which the glass reached equilibrium in this region shows that (1) the initial speed decreases with decrease in temperature and (2) as contain temperature the speed of transformation is a decreasing function of the time. For all temperatures below the lower limit if the region of transformation the glass is found in a single identical state of equilibrium and remains in that state as long as the temperature is not raised higher than the lower limit of the region of transformation. Knowledge of the law of transformation permits an explanation of the defects of tempered glass such as aging and heterogeneity and the estimation of the relative importance of these defects for different uses of the glass.
