_APPLICATION 54._ Explain why only one wire is needed to telegraph between two stations; why you should not turn an electric light on or off while standing in a tub of water. _APPLICATION 55._ In a house in the country, the electric wires passed through a double wall. They were separated from each other and well covered with insulation, but they were not within an iron pipe, as is now required in many cities. The current was alternating. One night when the lights were out a rat in the wall gnawed through the insulation of the wire and also gnawed clear through one of the wires. Did he get a shock? The next morning, the woman of the house wanted to use the electric iron in the kitchen and it would not work. The kitchen had in it a gas stove, a sink with running water, a table, a couple of chairs, and the usual kitchen utensils. There was also a piece of wire about long enough to reach across the kitchen. The electrician could not come out for several hours, and the woman wanted very much to do her ironing. Figure 130 is a diagram of the wires and the kitchen. Show what the woman might have done in order to use her iron until the electrician arrived. [Illustration: FIG. 130. How can the electric iron be used after one wire has been cut?] _APPLICATION 56._ A man wanted to change the location of the wiring in his cement-floored garage. While he was working, would it have been best for him to stand on the bare cement floor, on a wire mat, on an old automobile tire, on a wet rug, or on some skid chains that were there? INFERENCE EXERCISE Explain the following: 331. An ungreased wheel squeaks. 332. Lightning rods extend into the earth. 333. A banjo player moves his fingers toward the drum end of the banjo when he plays high notes. 334. When the filament breaks, an electric lamp will no longer glow. 335. An inverted image is formed by the lens of a camera. 336. A blown-out fuse may be replaced temporarily with a hairpin or with a copper cent. 337. Sparks fly when a horse's shoe hits a stone. 338. A room requires less artificial light if the wall paper is light than if it is dark. 339. Phonographs usually have horns, either inside or outside. 340. An electric car needs only one wire to make it go. SECTION 37. _Resistance._ What makes an electric heater hot? Why does lightning kill people when it strikes them? What makes an electric light glow?