Some contemporary advances in physics — V

IN considering such topics as the flow of electricity through solids and the outflow of electricity across their boundaries, wc have to forego the assistance of the great system of laws, models, and word-pictures which constitutes the contemporary theory of the structure of the atom. This imposing and truly powerful theory, which nowadays seems to bulk larger than all of the rest of physics, is after all limited to certain restricted fields; it deals successfully with particular properties of isolated atoms, and also with certain qualities of atoms which seem to be localized in their inner regions; but it avails little or nothing in the study of the behavior of liquids and solids. Much of the present-day theory of electrical conduction in solids is based only on the very simplest assumptions as to the nature of the atoms of which they are built, some would even remain valid under the old-fashioned ideas of continuous electrical fluids; and profoundly as we may believe that solids are built of atoms resembling Bohr's famous model, it is highly doubtful whether that model has ever helped to interpret a single one of the phenomena of conduction or done more than to provide a new language for old ideas.