The volume presented here to the reader is a series of partly interrelated monographs, bearing on several applications of X-ray diffraction. As is well known, the first application of X-ray diffraction was the investigation of the structure of crystals. Thi application has been and still is of paramount importance in physics, chemistry and mineralogy. It is based primarily on the concept of an ideal lattice structure, though corrections have to be made for the deviations of this structure occurring in real crystals.