A ball of cord, a pickax, a crowbar, some harness, a wooden wagon tongue, a whip, a piece of iron wire around a bale of hay (the wire was not long enough to stretch the whole distance between the two ends of the telegraph wire, even if you think he might have used it to patch the gap), a barrel with four iron hoops, and a rope. Which of these things could he have made use of in connecting the broken ends of the telegraph wire? [Illustration: FIG. 122. Which should he choose to connect the broken wires?] _APPLICATION 51._ A man was about to put in a new socket for an electric lamp in his home. He did not want to turn off the current for the whole house, as it was night and there was no gas to furnish light while he worked. "I've heard that if you keep your hands wet while you work, the film of water on them will keep you from getting a shock," his wife said. "Don't you wet your hands, Father," said his 12-year-old boy; "keep them dry, and handle the wires with your pliers, so that you won't have to touch it." "I advise you to put on your canvas gloves while you work; then you can't get a shock," added another member of the family. "That's a good idea," said the wife, "but wet the gloves, then you will have the double protection of the water and the cloth." The man laughed and went to work on the socket. He did not get a shock. Which advice, if any, do you think he followed? INFERENCE EXERCISE Explain the following: 311. A red postage stamp looks greenish gray in the green light of a mercury-vapor lamp. 312. Cracks are left between sections of the roadbed in cement auto highways. 313. Electricity goes up a mountain through a wire. 314. It is impossible to stand sidewise against a wall on one foot, when that foot touches the wall. 315. A charged storage battery will run an electric automobile. 316. An empty house is noisier to walk in and talk in than is a furnished one. 317. Lightning rods are made of metal. 318. It is harder to hold a frying pan by the end of the handle than by part of the handle close to the pan. 319. Diamonds flash many colors. 320. In swimming, if you have hold of a fastened rope and try to pull it toward you, you go toward it. SECTION 35. _Complete circuits._ Why does a doorbell ring when you push a button? Why is it that when you touch one electric wire you feel no shock, while if you touch two wires you sometimes get a shock? When a wire is broken in an electric light, why does it not light?