Fine-structure in spotty electron diffraction riiig patterns has previously been observed for specimens made up of MgO smoke particles of cubic morphology. This fine-structure was shown to arise from refraction effects in the small cubes (Sturkey & Frevel). We have recently observed a different type of fine structure in patterns from MgO films prepared by vacuum deposition (Fig. 1). This fine-structure consists of sets of regularly spaced fringes occurring at random orientations in the rings. The fringes may be seen in Fig. 2 which shows a segment of the (200) ring magnified 7x from the pattern in Fig. 1. It was considered possible that each set of fringes might arise from two superimposed diffraction’ spots from suitably situated crystallites in the specimen. Experiments have been conducted which clearly demonstrate that the fringes do in fact arise in this way.
