An electron microscope is described in which a range of magnifications between 1000 and 100,000 times can be covered continuously. This is achieved through the use of an intermediate projector lens.The principles of design are briefly discussed and the construction of the microscope and the high frequency‐operated 100‐kv power unit is dealt with in some detail. The instrument is provided with objective apertures to enhance image contrast and to permit operation with dark field illumination.Data is given relating to the electron optical system and it is shown how the instrument can be used to obtain electron diffraction patterns characteristic of small areas of a specimen under microscopic observation. The alignment procedure is briefly described and some typical micrographs are shown.