_APPLICATION 57._ A power company wanted to send large quantities of electricity down from a mountain. Should the company have obtained resistance wire or copper wire to carry it? Should the wire have been large or fine? _APPLICATION 58._ A firm was making electric toasters. In the experimental laboratory they tried various weights of resistance wire for the toasters. They tried a very fine wire, No. 30; a medium weight wire, No. 24; and a heavy wire, No. 18. One of these wires did not get hot enough, and it took so much electricity that it would have been too expensive to run; another got so hot that it soon burned out. One worked satisfactorily. Which of the three sizes burned out? Which was satisfactory? INFERENCE EXERCISE Explain the following: 341. If you attach one end of a wire to a water faucet and connect the other end to an electric lamp in place of one of the regular lighting wires, the lamp will light. 342. The needle of a sewing machine goes up and down many times to each stroke of the treadle. 343. Trolley wires are bare. 344. If you had rubbers on your feet, you could take hold of one live wire with perfect safety, provided you touched nothing else. 345. If you were on the moon, you would look up at the earth. 346. Toy balloons burst when they go high up where the air is thin. 347. You have to put on the brakes to stop a car quickly. 348. Telephone wires are strung on glass supporters. 349. If you pour boiling water into a drinking glass, frequently the glass will crack. 350. An asbestos mat tends to keep food from burning. [Illustration: FIG. 132. Pencils ready for making an arc light.] SECTION 38. _The electric arc._ How can electricity set a house on fire? THIS IS ONE OF THE MOST IMPORTANT SECTIONS IN THE BOOK. Do you know that you can make an arc light with two ordinary pencils? The next experiment, which should be done by the class with the help of the teacher, shows how to do it.