I made the electron bundle pass a bored-out spherical condenser with fine-meshed spherically shaped grids fixed over each end of the bore. With this arrangement I obtained laterally inverted images in the correct imaging scale. Somewhat later I found a solution which was unfortunately only theoretically correct. In analogy to the refraction of the light rays on their passage through the optical lens at their surfaces (“Grenzflächen), I wanted to use, for the electrical lens, the potential steps at corresponding surfaces, which are shaped like glasses lenses. Thus, the energy of the electron beams is temporarily changed-just like light beams on passage through optical lenses. For the realization of this idea, on each side of the lens two closely neighboured fine-meshed grids of the shape of optical lenses are required which must be kept on electrical potentials different from each other.First attempts confirmed the rightness of this idea, but at the same time also the practical inaptness of such grid lenses because of the too-strong absorption of the electron beam at the four grids and due to the field distribution by the wires.
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