The Electric Machine is shown in the illustration (fig. 212). It consists of a large plate of glass fixed upon a glass stand, between wooden supports. The handle is of glass; two pairs of rubbers are fastened above and below; the plate is turned between them, and becomes “positively” electrified. The rubbers are covered with leather and stuffed with horsehair, DD, and press very tightly against the glass, so that the friction is constant. The rubbers are covered with an amalgam made of mercury, zinc, and tin, two parts of the first to one each of the others. A chain (of metal) connects the machine with the ground. The conductors, PP, are united by a cross-piece, Q, and sustained upon glass supports. At the end of the conductors are two curved rods, CC, which are provided with points to take the electricity from the plate, but do not touch it. [Illustration: Fig. 212.—The Electric Machine.] The electricity is thus stored in the insulated conductors as the machine is turned. The negative portion is carried into the ground by the chain from the rubbers, while the positive electricity is retained. The longer we turn the more we shall obtain, and the quantity is measured by an electric pendulum on one of the conductors, which flies out by degrees as the charge increases, and indicates its power by means of a needle it works upon an ivory index. It is not difficult to make an electric machine out of a glass bottle. This will furnish the glass cylinder. If a stick be run through it (for which purpose a hole must be drilled in the bottom of the bottle), a handle can be fixed, and the bottle mounted on a stand. A wash-leather cushion, stuffed, can be so arranged that it will press against the bottle as it is turned; a piece of silk should be permitted to hang from the cushion frame over the glass. A conductor may be made from a piece of wood neatly rounded and smoothed, and coated with tinfoil. The ends should be rounded like “knobs.” Stick pins in to collect the electricity (and it will be readily obtained). The cushion should of course be well smeared with amalgam. From this, as well as from the glass-plate machine, the “positive” electricity can be drawn off and stored in a Leyden jar, and then discharged by the “discharging rod,” which is represented on the cut. It may have one or two handles, and one knob is placed outside the jar, the other near the ball surmounting it. The glass being a non-conductor saves the operator, and some long sparks and loud reports may be obtained. [Illustration: Fig. 213.—Cylinder machine.] The Electric Machine is always assumed to give off _positive_ electricity.