In the above-quoted work, page 61, is a description of Wimshurst's influence machine, one of the most recent and most powerful, which we condense as follows: This machine was produced about 1883. It consists of two circular disks of thin glass fourteen and one-half inches in diameter in the sample described, attached at their centers to loose bosses, so as to be rotated by cords and pulleys operated by a handle, in opposite directions. The disks rotate parallel with each other and are not more than one-eighth of an inch apart, and have their surfaces well varnished; and attached by cement to their outer surfaces are twelve or more radial, sector-shaped plates of thin brass- or tin-foil, disposed around the disks at equal distances apart. These sectors take the place of the "inductors" of Holtz's instrument, and appear to act also as carriers, though the exact nature of their action is somewhat mysterious. It appears, however, probable that those acting for the time as carriers on the one disk act at the same time as inductors on the other. The two sectors on the same diameter of each disk, at opposite sides of the center, are twice in each revolution momentarily placed in metallic connection with one another by means of a pair of fine wire brushes attached to the ends of a bent metal rod loosely pivoted at the center of each disk, the metal sectors just grazing the tips of the wire brushes as they pass. There is one of these bent rods on the outside of each disk, and their position as pivoted on their center can be varied at will, both with reference to the one on the opposite side and to the position of the fixed collecting combs. The efficiency of the machine varies with their position, and the maximum appears to be generally when the brushes touch the disks on diameters crossing the position of the collecting combs at about forty-five degrees, and with the bent rods on opposite sides at right angles to each other. The collecting combs are simple forks with collecting points turned inward, which forks embrace the opposite sides of the disks outside, which freely rotate between them, and they are supported on insulated posts. These supports may be small Leyden jars or condensers, with discharging knobs, or may be connected with similar condensers at a distance, or arranged in batteries or otherwise. The presence of the collecting combs is not necessary to the operation of the machine, their sole function being to carry away the positive electricity as generated. The machine is self-exciting, and it is believed that the initial action must be due to friction in the layer of air contained between the plates, which, as above stated, are only about one-eighth of an inch apart. It is nearly independent of atmospheric conditions, and not liable to reverse its polarity, as are the Voss machines. The Voss machine uses a larger glass disk which does not rotate, but is fixed, and which has a central opening