The cathode consists of a small aluminium disk placed at the narrowest end of the tube, while the anode, consisting of a small aluminium rod, is placed laterally, in the widest part of the tube, at 14.5 cm from the cathode. Further on, at the same distance from the anode, an aluminium diaphragm with a small hole in the centre limits a thin beam of electrons which, on striking a screen of calcium tungstate placed at the widest end of the tube, generates a small, circular, luminous notch.
Between the diaphragm and the screen, where the tube has an intermediate width, two small rectangular aluminium plates facing and parallel to each other, create an electric field perpendicular to the direction of the beam when their potentials differ.
At that point the beam is deflected towards the positive plate and the consequent shift of the luminous notch on the screen, in the direction perpendicular to the plates, can be measured, since it is divided into millimetres. ...continues