Some theoretical problems concerning the solid state

This paper contains a discussion of some of the unsolved theoretical problems connected with the solid state of matter. One of these is the occurrence of small crystallites even in the most perfect crystals. Reasons are given for attributing such imperfections in crystals to the conditions of growth from the melt. It is pointed out that a study of the conditions prevailing at the boundaries between crystallites might throw light on slip and on the appearance of slip bands - properties of crystals which have not yet been adequately explained. The nature of melting and the converse process of solidification require further study. Local melting may occur in crystals owing to slip and be a factor in producing strain hardening. A method is given of evaluating the relation between stress and strain outside the usual elastic limits and at temperatures approaching the melting temperature.