You will remember why sailors dared not venture far out upon the ocean and search for a water route to the Eastern countries and islands. The time was soon coming, however, when they would dare to do so, and two wonderful inventions helped navigators very much. One came from the finding of the loadstone, or natural magnet. This is a stone which has the power of attracting iron. A steel needle rubbed on it becomes magnetized, as we say, and, when suspended by the center and allowed to move freely, always swings around until it points north and south. Hung on a pivot and inclosed in a box, this instrument is called the mariners' compass. It was of great importance to sailors, because it always told them which way was north. On cloudy days, and during dark, stormy nights, when the sun and stars could not be seen, the sailors could now keep on their way, far from land, and still know in which direction they were going. [Illustration: Mariners' Compass.] The other invention was that of the astrolabe. This was an instrument by means of which sailors measured the height of the sun above the horizon at noon, and could thus tell the distance of the ship from the equator. It is in use on all the ships at the present time, but it has been greatly improved, and is now called the quadrant. The compass and the astrolabe, together with improved maps and charts, made it possible for navigators to tell where their ship was when out of sight of land or in the midst of storm and darkness. This made them more courageous, and they ventured a little farther from the coast, but still no one dared to sail far out upon the Sea of Darkness. COLUMBUS. One day a man appeared in Portugal, who said he was certain that the earth was round, and that he could reach India by sailing westward. Every one laughed at him and asked him how he would like to try. He answered that he would sail round the earth, if any one would provide him with ships. [Illustration: Christopher Columbus.] People jeered and scoffed. "If the earth is a sphere," they said, "in order to sail round it you must sail uphill! Who ever heard of a ship sailing uphill?" But this man, whose name was Christopher Columbus, remained firm in his belief. When a boy, Columbus had listened eagerly to the stories the sailors told about strange lands and wonderful islands beyond the water. He was in the habit of sitting on the wharves and watching the ships. Often he would say, "I wish, oh, how I wish I could be a sailor!" At last his father, who was a wool comber, said to him, "My son, if you really wish to become a sailor, I will send you to a school where you will be taught navigation." Columbus was delighted at this, and told his father that he would study diligently. He was sent to the University of Pavia, where he learned all the geography that was then known, as well as how to draw maps and charts. He became a skillful penman, and also studied astronomy, geometry, and Latin.