CHAPTER I MAGNETS AND MAGNETISM
Over two thousand years ago, in far-away Asia Minor, a shepherd guarding his flocks on the slope of Mount Ida suddenly found the iron-shod end of his staff adhering to a stone. Upon looking further around about him he found many other pieces of this peculiar hard black mineral, the smaller bits of which tended to cling to the nails and studs in the soles of his sandals.
This mineral, which was an ore of iron, consisting of iron and oxygen, was found in a district known as Magnesia, and in this way soon became widely known as the "Magnesstone," or magnet.
This is the story of the discovery of the magnet. It exists in legends in various forms. As more masses of this magnetic ore were discovered in various parts of the world, the stories of its attractive power became greatly exaggerated, especially during the Middle Ages. In fact, magnetic mountains which would pull the iron nails out of ships, or, later, move the compass needle far astray, did not lose their place among the terrors of the sea until nearly the eighteenth century.
For many hundreds of years the magnet-stone was of little use to mankind save as a curiosity which possessed the power of attracting small pieces of iron and steel and other magnets like itself. Then some one, no one knows who, discovered that if a magnet-stone were hung by a thread in a suitable manner it would always tend to point North and South; and so the "Magnes-stone" became also called the "lodestone," or "leading-stone."
These simple bits of lodestone suspended by a thread were the forerunners of the modern compass and were of great value to the ancient navigators, for they enabled them to steer ships in cloudy weather when the sun was obscured and on nights when the pole-star could not be seen.
The first real compasses were called gnomons, and consisted of a steel needle which had been rubbed upon a lodestone until it acquired its magnetic properties. Then it was thrust through a reed or short piece of wood which supported it on the surface of a vessel of water. If the needle was left in this receptacle, naturally it would move against the side and not point a true position. Therefore it was given a circular movement in the water, and as soon as it came to rest, the point on the horizon which the north end designated was carefully noted and the ship’s course laid accordingly.
The modern mariners’ compass is quite a different arrangement. It consists of three parts, the bowl, the card, and the needle. The bowl, which contains the card and needle, is usually a hemispherical brass receptacle, suspended in a pair of brass rings, called gimbals, in such a manner that the bowl will remain horizontal no matter how violently the ship may pitch and roll. The card, which is circular, is divided into 32 equal parts called the points of the compass. The needles, of which there are generally from two to four, are fastened to the bottom of the card.
