中国四大发明――指南针Four greatest inventions of ancient China--- compass

古时候，人们外出辨别方向，白天看太阳，晚上看星星，遇到阴天雨天就困难了。

传说，中国人的祖先黄帝制造了能指示方向的指南车，如果这个传说真实的话，那么，中国远在4000年以前就有能指示方向的工具了。不过，指南车是靠齿轮转动来指方向，它还不是我们要讲的指南针。

很早以前，中国劳动人民就发现了能吸铁的天然磁石。2000年前的战国时期，人们把天然磁铁做成一个勺子，放在光滑的铜盘上，转动勺子，等勺子停下来，勺把儿总是指向南方，这就是最早的指南工具，名字叫“司南”。

宋代，中国人发明了人工磁铁。人们把铁片做成鱼形，放在火里烧红，按南北方向放在地上，铁片受地磁感应带有了磁性，这就是“指南鱼”。不过，指南鱼的磁性很小。后来，人们又把钢针在天然磁铁上摩擦，使钢针带有磁性，这就是针形指南针。据记载，宋代有四种针形指南针，其中有一种水浮法指南针最早用在了航海事业上。不久，人们又把磁针与方位盘结合在一起，制造出了罗盘针。罗盘针的应用促进了航海事业的发展。明代著名航海家郑和七次西洋远航，用的就是罗盘针。

In ancient time，people tell direction by looking up at sun in daytime and star at night, but it became difficult when meets a bad weather.

According to the old tradition，yellow emperor, the ancestors of the Chinese people, made a kind of vehicle that can show the direction, people called it “southward pointing cart”. If the legend is true, it means China already invent the implement that can tell direction. But, southward pointing cart is not the compass that we are talking about.

Long before, Chinese people noticed the lodestones (a mineral composed of an iron oxide which aligns itself in a north-south direction). They designed the compass on a square slab which had markings for the cardinal points and the constellations. The pointing needle was a lodestone spoon-shaped device, with a handle that would always point south. it’s the earliest direction device, we called it “Sinan”.

In the Song Dynasty, Chinese invent artificial magnet, they made an iron as a fish form, burned it red in the fire, and put it on the ground according to the north and south direction, then, the sheet iron became with magnetism, it is the "guide fish", but the magnetism of this guide fish is too weak, so people improved it to be magnetized needles. Soon, people designed a compass by combining magnetized needles with azimuth card. Then compass used instead of the guide fish, and between 850 and 1050 they seem to have become common as navigational devices on ships.

The first person recorded to have used the compass as a navigational aid was Zheng He (1371-1435), from the Yunnan province in China, who made seven ocean voyages between 1405 and 1433.