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.
Fig. 213.—Cylinder machine.
The Electric Machine is always assumed to give off positive electricity.
Sir William Armstrong’s Electric Machine is a mode of obtaining electricity by moist steam. The design is Armstrong’s, and Professor Faraday subsequently went into all the conditions to produce the “fluid” by the friction of steam. The machine was something like a small boiler supported on glass legs. A row of nozzles was fixed upon the escape pipe so as to create a great velocity and friction in the escaping steam. Round the nozzles was a box of cold water, for that fluid was found necessary for the production of electricity as demonstrated by Professor Faraday. The steam rushed against a row of points attached to the prime conductor of an electric machine, and the electricity of the steam was thus given off to the conductor. There are many other forms of electric machines, but it will serve no purpose to detail them.
Fig. 214.—Discharging rod.