THE COMPASS. One of these instruments was the compass, which the Chinese had long used, and which was known to the Arabs before the Europeans heard of it. If a boy will take a needle, rub its point with a magnet, and lay the needle on a cork floating in water, he will have a rough sort of compass. The point of the needle wherever it may be turned will swing back towards the north, thus guiding the sailors. [Illustration: MARINER'S COMPASS] The compass was known in Europe about 1200. There is a story that at first sailors thought its action due to magic and refused to sail under a captain who used it. But a century later it was in general use, and had been so much improved that even in the severest storms the needle remained level and pointed steadily towards the north. [Illustration: AN ASTROLABE] THE ASTROLABE. The other instrument, called the astrolabe, was a brass circle marked off into 360 degrees. To this circle were fastened two movable bars, at the ends of which were sights, or projecting pieces pierced by a hole. The astrolabe was hung on a mast in such a way that one bar was horizontal and the other could be moved until through its sights some known star could be seen. The number of degrees marked on the circle between the two bars told how high the star was above the horizon, and the sailors could reckon the latitude of the place where they were. In a similar way their longitude could be found out. The astrolabe was not so useful as the compass, for it could be used only on clear days or nights. With these two instruments it was possible to sail far out into the Atlantic. By the middle of the fourteenth century ships from Genoa and Portugal had visited the Madeira and the Canary Islands, and even the Azores which are a thousand miles from the mainland. WHAT MEN THOUGHT ABOUT A SEA ROUTE TO THE EAST. Men learned more about other strange lands through a Venetian traveler, Marco Polo, who wrote an account of his wonderful journey to the court of the Grand Khan, or Emperor of the Mongols, of his travels through China, and of his return to Persia by sea. Many men in the Middle Ages had believed that east of Asia was a great marsh, and that because of it even if they succeeded in sailing around Africa it would be impossible to reach the region of the spices and silks and jewels which they so much desired. They also thought that the heat in the tropics was so intense that at a certain distance down the coast of Africa they would find the water of the ocean boiling. These things and the tales of strange monsters that inhabited the deep sea had terrified them. The news which Marco Polo brought changed this feeling.