An electrostatic printing tube for electronic duplication

When the electron beam of a cathode-ray tube strikes the ends of a linear array of parallel wires passing through the faceplate, the wires begin to charge toward cathode potential. If a sheet of dielectric material backed by a ground plane is placed close to the other ends of the wires, a discharge will take place when a given wire has reached a critical value of voltage. The resulting spot of charge on the dielectric can be made visible by application of charged powder.