APPLICATIONS of the sealed-off cathode-ray XX tube to the field of radio have been previously well treated, so the author gains by concentrating on other applications, which are shown to be wide and valuable. Controlling electron beams in'cathode-ray tubes, electron diffraction tubes, and electron micro scopes exhibits many common features, and the author brings these and related topics up to date in book-form. He also shows that the sealed-off glass tubes and the metal continuously evacuated tubes have their separate fields of application and are not always competitors. He gives some of the latest electron microscope photographs, and shows how essential this new instrument is in many fields of research. It is unfortunate that the War has further retarded the development of electron microscopes in Great Britain, an opportunity which even private generosity has neglected. The text is well produced considering the present conditions, and includes the essential references. The Cathode Ray Oscillograph in Industry By Dr. W. Wilson Pp. xii + 150 + 42 plates. (London: Chapman and Hall, Ltd., 1943.) 12s. 6d. net.