305. Relate the accident which occurred at St. Petersburg. What is said of lightning-rods?
306. What was Sulzer's experiment? What were Galvani's observations?
307. What is said of the pile of Volta? What of his cup battery and of other batteries?
308. What difference is there between frictional and voltaic electricity?
CHAPTER XVI.
308. What are loadstones? Where do they abound? What is said of discoveries in magnetism? Whence come the terms magnetism and magnet?
309. What is said of the attraction of magnetism? What law is there in regard to it? What is said of the poles of a magnet? What of magnetism by induction?
310. What is said of attraction and repulsion in magnets? Explain the formation of the curves of iron filings in the experiment represented in Fig. 282.
311. How may artificial magnets be made? What is said of the horseshoe magnet and its armature?
312. What is said of the magnetic needle and the mariner's compass?