9. In Application 55, page 228, if the rat had gnawed the wire in two while the electric iron was being used, would anything have happened to the rat? Would there have been any danger to the house? 10. Where a wire is screwed into an electric-light socket, what harm, if any, might result from not screwing it in tightly? 11. How can a wire be safely spliced? 12. Why is an electric arc in a circuit dangerous? INFERENCE EXERCISE Explain the following: 351. White objects look blue when seen through a blue glass. 352. When you pull the plug out of an electric iron, the iron cools. 353. People who do not hear well sometimes use speaking trumpets. 354. The sounding board of a piano is roughly triangular; the longest strings are the extreme left, and those to the right get shorter and shorter. 355. Birds can sit on live wires without getting a shock. 356. Deaf people can sometimes identify musical selections by holding their hands on the piano. 357. An electric toaster gets hot when a current passes through it. 358. The cord of an electric iron sometimes catches fire while the iron is in use, especially if the cord is old. 359. If a live wire touches the earth or anything connected with it, the current rushes into the earth. 360. When you stub your toe, you have to run forward to keep from falling. SECTION 39. _Short circuits and fuses._ Why does a fuse blow out? Sometimes during the evening when the lights are all on in your home, some one tinkers with a part of the electric circuit or turns on an electric heater or iron, and suddenly all the lights in that part of the house go out. A fuse has blown out. If you have no extra fuses on hand, it may be necessary to wait till the next day to replace the one that is blown out. It is always a good idea to keep a couple of extra fuses; they cost only 10 cents each. And if you do not happen to know how fuses work or how to replace them when they blow out, it will cost a dollar or so to get an electrician to put in a new fuse. The next three experiments will help you to understand fuses. [Illustration: FIG. 136. _A_, the "fuse gap" and _B_, the "nail plug."]