II. The Fracture of Homogeneous Media

Geologists are concerned with the origin and growth of worlds, in the evolution of which all the complex forces of Nature are involved. To elucidate the mystery of the earth’s creation and to piece together the fragments of its past, the geologist applies the detailed knowledge of these forces as they are disclosed by workers in any of the varied spheres of science. By the application, for example, of the recently acquired knowledge of radio-activity, the earlier conceptions of the age of the earth have been profoundly modified. Geology as a science has no boundaries, and the observations, therefore, of an optical engineer concerning the surface phenomena and fracture of homogeneous media may be of interest to the members of this Society. Homogeneity is a relative term. According to Lord Kelvin— “The perfect fulfilment of this condition without any limit as to the smallness of the parts, though conceivable, is not generally regarded as probable for any of the real solids or fluids known to us, however seemingly homogeneous. . . . In other words, the prevailing belief is that every kind of matter with which we are acquainted has a more or less coarse-grained texture . . . and in the meantime,” continues Lord Kelvin, “we need only say that the definition of homogeneous may be applied practically on a very large scale to masses of building or coarse-grained conglomerate rock, or on a more moderate scale to seemingly homogeneous metals, or on a scale of extreme undiscovered fineness This 250-word extract was created in the absence of an abstract