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The object of the research was to study the spot patterns produced when an electron beam of homogeneous velocity ~ 30 kV is transmitted through a thin crystalline film. Such spot patterns were first reported by Kikuchi, and their importance lies in the fact that they are regarded as being due to single crystals of matter; the study of the diffraction of electrons by single crystals must necessarily precede the exact explanation of the Debye-Scherrer patterns obtained when random aggregates are employed. The results described below have a direct bearing on the latter problem. Electron diffraction spot patterns due to the transmission of 30 kV electrons have been studied by Thomson, Kirchner, Trillat and Hirsch, Lassen. But the interpretations of these pseudo-two-dimensional effects has remained uncertain.

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A spectrophotometer is described by means of which the spectral distribution of radiation from the sun and sky, or the sky alone, may be conveniently measured if the sky is either completely clear or completely overcast. The instrument is calibrated using a standard lamp, whose spectral energy distribution is known in the region 0.4 micron to 0.7 micron. A “fatigue-correcting” lamp, included in the optical system, enables the results to be expressed in energy units. Possible errors are discussed.