　　指南针的发明源于中国。　　2000多年前的战国时期，人们-名校题库网

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　　指南针的发明源于中国。

　　2000多年前的战国时期，人们利用磁铁在地球磁场中的南北指极性发明了指南针的雏形，称之为“司南”。它用天然磁石制成，样子像一把勺子，底部为圆形，可在平滑的“地盘”上自由旋转，待旋转的磁勺慢慢停止下来时，勺柄就指向南方。磁石的硬度为5.5—6.54。

　　900年前的北宋时期，人们把一片薄铁皮剪成约7厘米长，1.5厘米宽的鱼形，放在炭火中烧得通红，然后用鱼嵌夹着鱼头，让鱼尾正对着地球磁场方向。这样，铁鱼内部被烧得处于活动状态的磁畴就顺着地球磁场方向排列，再把磁化后的铁鱼迅速浸入冷水中，磁畴的规则排列就马上固定下来。这时，再把小鱼浮在水面平静的碗中，鱼头鱼尾就可以指南北了。在使用指南针的过程中，人们不断地改进，不断地摸索，使指向仪器在外形上终于成为最简便的针形。人们拿一根小钢针在磁石上反复摩擦，待钢针磁化后，便是指南针了。在此基础上，以后人们发明了更为先进的罗盘。

　　指南针首先是风水先生发明和使用的。北宋时期，指南针应用于航海事业中，使之有了经久不衰的生命力。北宋前，航海者是利用日月星辰的位置来判定方向。这种方法在天晴时尚可运用，一旦阴雨天，航海者的命运就难以把握了。

　　自从有了指南针，它为航海者带来极大的方便，成为航海家的必备之物。郑和七次下西洋，哥伦布对美洲大陆的发现和麦哲伦的环球航行，都与指南针的应用分不开。

正确答案及解析

正确答案

解析

The compass was invented in China.

　　Two thousand years ago, during the Warring States Period （475 B.C.—221 B.C.） in China, the Chinese invented “Sinan”, an embryonic form of compass, which made use of the magnet’s property that it always orients itself north and South in the magnetic field of the earth. It was made of natural magnetic lodestone and it looked like a spoon with a hardness of 5.5—6.5. Its bottom was round and so it could spin freely on the tray on which it was placed. When the revolving spoon slowed down and came to a stop, its handle pointed to the south.

　　Nine hundred years ago, in the Northern Song Dynasty （960 A.D.—1127 A.D.）, the Chinese made a thin iron sheet shaped like a fish, which was 7 cm in length and l.5 cm in breadth. It was heated red hot in a charcoal fire. The fish head was then gripped with a pair of tongs and the fish tail was turned to the direction of the magnetic field of the earth. The moving magnetic domain inside the hot fish was thus aligned in the same direction as the magnetic field of the earth. The magnetized fish was then put suddenly into cold water, thus fixing the magnetic field in the fish. Therefore, when the fish was floated on still water in a bowl, the head of the fish pointed to the south and the tail to the north. Over years, this fish-shaped device gradually evolved into the more simple and convenient form of an iron needle. To make it, a small needle was repeatedly rubbed on a piece of magnetite till it was magnetized. The more advanced compass was invented on the basis of it afterwards.

　　The compass was first invented and used by men who help people to determine whether the layout and the position of their homes and offices are in good relation to the environment. In the Northern Song Dynasty, it was used in navigation, therefore gaining a lasting life. Before that time, navigators determined directions by looking at the positions of the sun, the moon and the stars. This method was useful when the sky was clear. It was, however, difficult to ensure a navigator's destiny when the sky was overcast or rainy.

　　Ever since the use of the compass, navigation became much easier and for the navigators, it became indispensable. For example, Zheng He, the famous Chinese navigator in the Ming Dynasty, went seven times （1405 A.D.—1433 A.D.） to more than 30 countries in Asia and Africa by sea. Christopher Columbus discovered the Americas, and Ferdinand Magellan made a voyage around the world by sea. All of these voyages would not have been successful without making use of the compass.