A Note on the Diffraction of Cathode Rays by Single Crystals

The black and white line parabolas and circles observed in the diffraction patterns of electrons are shown to be a kind of envelope of the family of Kikuchi lines due to a set of co-zonal planes. That the parabolas appear isolated from the generating Kikuchi lines is due to an effect similar to that which in the case of x-rays accounts for the reduction in density observed at the intersection of two lines in the diffraction pattern. The circle is in fact the envelope of a family of parabolas, its appearance isolated from the generating lines being accounted for in the manner mentioned above. It is shown that the circle is the boundary of a region within which occur no Kikuchi lines of a certain set.