The prehistory of solid‐state physics

Prehistory implies the selection of a date when history begins. In solid‐state physics this is very recent, dating, perhaps, from Debye’s specific‐heat theory of 1913, but most of all from the famous diffraction experiment of Friedrich, Knipping, and Von Laue in March 1912. It was this tool of perfection which laid the ground for imperfection to become of interest to physicists. The growth of solid‐state physics marks, I think, a basic change in the attitude of physicists toward matter. Virtually all the development of mechanics, marvellous though it was, was based on a treatment of matter that was essentially structureless and whose measured elastic constants and densities gave the constants to put into equations that became ever more elaborate. When physicists at last paid attention to the structure of real crystals, they soon became aware of imperfections, both theoretically and experimentally, and the great flourishing of solid‐state physics in the last three decades has been mostly based on the elucidation of the role of mechanical, ionic, and electrical imperfections in a crystal, accompanied, of course, by a continued development of understanding of bonding and dynamics of the ideal lattice.