Holtz (1836-1913) and by J. Robert Voss, a mechanician from Berlin. Voss devised this self-excitation model in 1880, perfecting a machine presented by Topler the previous year. The machine rests upon a footed walnut base. A column horizontally supports the axis of rotation. Two thin, shellacked, parallel glass disks in close proximity one to the other are vertically hinged to this axis. The larger of the two (the rear one), is a fixed disk and rests on the base along the groove of an ebonite insulation disk; the other (the front one), is a smaller mobile disk and rotates by means of a crank that controls a pair of pulleys connected by a cord. On its outer side, the fixed disk carries the inductors, two strips of tinfoil glued in the middle of two, broad paper shields placed diametrically, one beside the other. The mobile disk carries the Toepler-Voss self-excitation system consisting of six metallic buttons, each surrounded by a ring of tinfoil, placed equidistantly in a circle. Two small metal brushes rub against the buttons; the brushes are fixed to a curved conductor (covered with ebonite) that is clamped to the disks at opposite points and is in contact with the inductor’s tinfoil strips. In front of the buttons, fixed to the edge of the mobile disk towards the horizontal diameter, two brass collection combs, each having 10 points, are positioned in the direction of the disk. The combs are in contact with the inner shields of two Leiden jars, and with the arms of the spark-gap, two brass bars equipped with spherules and insulation handles, into which the sparks are released. The outer shields of the Leiden jars rest on two brass disks electrically connected by a metallic wire, which passes along the base. A second pair of collection combs, facing the mobile disk, each with eight points and a central metal brush that rubs against the buttons, comprises the so-called “diametrical conductor”. The “diametrical conductor” is inclined at 45° with respect to the horizontal diameter and allowed for the polarity of the linings to be maintained unaltered, especially when the exciting dynamos moved farther away than their normal explosive distance. Not even a weak initial charge is needed to start the machine; the self-excitation system automatically starts by turning the mobile disk clock-wise (when viewed from the front of the machine) using the special crank. The quantity