By means of two coils connected in series placed on either side of the tube and normal to the two plates, it is possible to create a magnetic field perpendicular to the direction of the electric field and to that of the beam, which causes a deviation of the notch [???] on the screen, still in the direction perpendicular to the plates; by regulating the direction and intensity of the current in the coils it is possible to compensate exactly for the deviation produced by the magnetic field with the one produced by the magnetic field.
In such conditions a simple relation is found which binds the ratio between the charge and the mass of the electron to the intensities of the two fields, to the geometrical characteristics of the device and to the deviation of the luminous notch on the screen produced initially by the electric field.