But Papin died a few years afterwards without being able to carry out his great ideas beyond constructing a paddle-boat. He was one of the world’s greatest inventors, but the engineers of his time were not able to carry out his great inventions. Though his engine differs very greatly from the steam-engines now made, it certainly contained a piston working in a cylinder, and a safety valve, which are essential parts of a modern steam-engine. CHAPTER IX ELECTRIC SPARKS WHEN the ships of the Carthaginians sailed round the coast of Spain and France so far as Cornwall, to sell their purple cloth in exchange for tin, they sometimes brought home with them small pieces of a stone which had the colour of gold, but was transparent, and could be cut more easily than glass. This stone came from the shores of Germany, mostly from the Baltic Sea. It was not really a stone, but the hardened sap of a sort of pine tree, which had lain long underground; and it sometimes showed traces of forest life, such as bodies of insects, embedded in it. This stone, or “amber” as we call it now, was a source of wonder and delight to the ancient Greeks and Romans. It was thought to possess all kinds of magic properties. Besides looking very beautiful in a necklace it was supposed to have a kind of soul of its own; for it sometimes attracted little pieces of straw, or dust. The ancients could only imagine that this was the effect of some kind of will or desire possessed by the amber. They only knew of one other substance which showed similar power. This was the lodestone which attracted iron, and which the ancients therefore sometimes called “quick iron,” meaning “living iron,” just as the lively liquid mercury was called quicksilver. It was Dr. Gilbert of Colchester who first proved that these two powers are entirely different from each other. He called the power shown by amber “electric” power, and the power shown by lodestone he called “magnetic” power. Electric power, he said, had to be excited by rubbing the amber with a piece of cloth; but magnetic power could only be excited in a piece of iron by rubbing it with lodestone, or hanging it in a direction pointing to the North Pole. It was Dr. Gilbert also who invented a little instrument resembling a compass which showed electric attraction. It was a short piece of straw mounted on the point of a needle in the same way as a magnetic needle. Although Gilbert had proved that electric and magnetic forces are quite different, an event occurred in the year 1681 which showed that there is some kind of connection between the two. In that year a ship bound for Boston was struck by lightning. [Illustration: Fig. 46.--Gilbert’s Electric Needle.]