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Abstract
Under certain conditions favouring the growth of cubic grains, a small proportion are formed in which one half is rotated with respect to the other half about an axis normal to their common (100) plane. The projective areas of such grains are much larger than those of normal cubic grains in the same emulsion. Possible angles of rotation and their relative frequency are calculated on t/ie supposition that in the planes of contact of the two halves, some ions, at least, are in their normal positions with respect to their neighbours. Observed angles group closely around the calculated ones and there is broad agreement as regards the relative frequency of occurrence. This demonstrates that the grains are single entities. It is shown that grains possessing a rotation are of low surface-image and high internal-image sensitivity. This situation can be attributed to preferential electron-trapping on or near the plane of rotation or associated regions of lattice misfit.