An electron‐diffraction unit incorporating a rotating sector has been developed which makes possible the accurate and objective measurement of the intensity of electrons diffracted by free atoms and molecules. The diffraction data afforded are sufficiently precise to permit the calculation of the distribution of electrons in atoms and the amplitude of vibration of atoms in molecules, as well as interatomic distances that are comparable in accuracy in suitable cases to those obtained by microwave spectroscopy. A description of the essential components of the unit is given together with some data on performance and discussion of the use of the apparatus.