With the modern machines large sparks are produced by merely turning a crank, enough electricity being produced to imitate a small thunderstorm. The sparks of home-made lightning will jump several inches.
Do not think that electricity is generated in a commercial way by static electric machines. The practical uses of static electricity are very few when compared with those of current electricity from batteries and dynamos.
15. Condensation of Static Electricity. By means of apparatus called condensers, a terrific charge of static electricity may be stored. Fig. 11 shows the most common form of condenser, known as the Leyden jar. It consists of a glass jar with an inside and outside coating of tin-foil.
| Fig. 11. | Fig. 12. |
To charge the jar it is held in the hand so that the outside coating shall be connected with the earth, the sparks from an electric machine being passed to the knob at the top, which is connected by a chain to the inside coating.
To discharge the jar, Fig. 12, a conductor with an insulating handle is placed against the outside coat; when the other end of the conductor is swung over towards the knob, a bright spark passes between them. This device is called a discharger. Fig. 13 shows a discharge through ether which the spark ignites.
Fig. 13.
16. The Leyden Battery, Fig. 14, consists of several jars connected in such a way that the area of the inner and outer coatings is greatly increased. The battery has a larger capacity than one of its jars. (For Experiments in Condensation, see "Study," Chapter X.)