The chief object of the investigation was to obtain quantitative information on the effect of screens, of which the dimensions are small compared with the wave-length of the waves they are intended to screen. Some preliminary experiments are described, in the first of which the screening effect of a totally closed iron tank was investigated by an operator inside it with a frame coil receiver; and in the second an investigation was made on the effect of screening a square frame receiving coil by totally enclosing each of its four sides in a metallic envelope. A description is then given of the method employed in subsequent experiments of measuring the effect of screens based upon the employment of two receiving coils connected in opposition. This is followed by an account of measurements made by this method on some specially constructed screens of straight wires, open and closed loops, and wire-netting, etc. These measurements demonstrate the important part played by closed circuits in screening the magnetic field of radio waves, and show that an effective screen may be constructed of wire-netting. In this connection a description is given of the screening of the interior of a hut with this material to protect direction-finding apparatus within it from “direct pick-up.”Further experiments, in which the effect of screens on the electric field of the waves is measured, are then described. Three types of screen investigated were shown to reduce substantially the electric field without affecting the magnetic field, while, later in the paper, it is shown that a fourth type will screen the magnetic field but not the electric field. A cage of the former type is then described which is now in practical use as a means of eliminating “antenna” effect from a single-coil direction-finder contained within it.A discussion of the experiments follows, some explanation of the various effects being given, and conclusions are drawn as to the general principles of screening and as to the essential points to be attended to in the design of efficient screens for various purposes.