a triboelectric device in which electrical charges are obtained by a rolling process between two rigid dielectric surfaces of appropriate materials , one of which may be planar . there exists therein no injection of electrical charges originating from outside . the separation of the charges with the concomitant generation of electrical potentials is effected by the movement of the parts by triboelectrification . such devices are useful in the construction of electrostatic generators for teaching , research or industry and as an essential supply for fixed or portable ignition devices for boilers , cookers and gas burners .