Imagine the problem you had if you were a traveler in uncharted territory five hundred years ago. If you had a clock and you could see the sun, you could get a decent sense of direction. Or at night, if you could see the stars and you had some time, you could also get a sense of direction. But wouldn't it be great if you could pull a device out of your pocket and it would immediately tell you your direction of travel in an instant? A compass seems so simple today. Any kid can make one in five minutes with a sewing needle, a refrigerator magnet, a little piece of foam, and a bowl of water. Rub the needle on the magnet to magnctize the needle and float it on the foam in the bowl. The needle will rotate, and you'll instantly know where magnetic north is. But rewind a thousand years and it's not so easy. First you need an iron needle. Which means you need iron — no small thing given the technology required to sinelt the ore. Assuming you can find the ore and know what it means. Then you need the ability to shape the iron into a needle, which requires tools and some finesse. And then you need a magnet. Where will you get one of those? Electromagnets don't exist yet. There are naturally occurring magnets called lodestones, but they are rare and you need to find one. Everything came together in China. During the Song Dynasty around 1040, they began to produce iron, and iron needles, which they combined with lodestones to make the first compasses. They hung their needles on strands of silk rather than floating them in a bowl of water. From an engineering standpoint, compasses were incredibly important to early surveying efforts. If you needed to lay out a railroad, a canal, or the boundary lines on a piece of land, a good compass was essential. There was no other easy, accurate way to get your bearings in the middle of nowhere. All because the core of the earth is itself a magnet, and instrument makers used that fact to create quality direction-finding instruments. >The magnetic compass was developed during the Song era of China.