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Summary The elementary concepts of crystal dislocation theory—in particular the Burgers vector, perfect and imperfect dislocations, sessile dislocations, extended dislocations, twin and twinning dislocations—are defined in a manner independent of particular crystal lattices or models or special orientations of the dislocation : and it is shown how their essential properties arise, in so far as they are independent of the particular crystal in which they occur.
F. C. Frank (Wed,) studied this question.