=170. Central Stations=, as the word implies, are places where, for example, electricity is generated for the incandescent or arc lights used in a certain neighborhood; where telephone or telegraph messages are sent to be resent to some other station; where operators are kept to switch different lines together, so that those on one line can talk to those on another, etc., etc. There are many kinds of central stations, each requiring a large amount of special apparatus to carry on the work. Fig. 249 gives a hint in regard to the way car lines get their power from a central power station. As a large part of the apparatus required in ordinary central stations has already been described, it is not necessary to go into the details of such stations. [Illustration: Fig. 249.] In lighting stations, for example, we have three principal kinds of apparatus. Boilers produce the steam that runs the steam engines, and these run the dynamos that give the current. Besides these there are many other things needed. The electrical energy that goes over the wires to furnish light, heat, and power, really comes indirectly from the coal that is used to boil water and convert it into steam. The various parts of the central station merely aid in this transformation of energy. [Illustration: Fig. 250.] [Illustration: Fig. 251.] The dynamos are connected to the engines by belts, or they are direct connected. Figs. 250, 251, show dynamos connected to engines without belts. The current from the dynamos is led to large switchboards which contain switches, voltmeters, ammeters, lightning arresters, and various other apparatus for the proper control and measurement of the current. From the switchboard it is allowed to pass through the various street mains, from which it is finally led to lamps, motors, etc. Water-power is frequently used to drive the dynamos instead of steam engines. The water turns some form of water-wheel which is connected to the dynamos. At Niagara Falls, for example, immense quantities of current are generated for light, heat, power, and industrial purposes. [Illustration] CHAPTER XXVII. MISCELLANEOUS USES OF ELECTRICITY. =171. The Many Uses= to which the electric current is put are almost numberless. New uses are being found for it every day. Some of the common applications are given below. =172. Automatic Electric Program Clocks=, Fig. 252, are largely used in all sorts of establishments, schools, etc., for ringing bells at certain stated periods. The lower dial shown has many contact-points that can be inserted to correspond to given times. As this revolves, the circuits are closed, one after the other, and it may be so set that bells will be rung in different parts of the house every five minutes, if desired. [Illustration: Fig. 252.] [Illustration: Fig. 253.]