北师大版高中英语模块7--Unit 20 New Frontiers 2
[00:03.47]Gunpowder was invented by the Chinese
[00:05.73]in the eighth century AD.
[00:08.28]Early Chinese scientists discovered
[00:10.64]that they could make an explosive substance
[00:12.76]by mixing sulphur,charcoal and saltpeter.
[00:16.76]Gunpowder was used in warfare
[00:18.93]and led to the development of many different
[00:21.00]kinds of weapons.
[00:22.77]For example, rockets carrying an explosive
[00:25.28]shell of gunpowder could be launched
[00:27.98]at enemy soldiers from a bamboo tube.
[00:32.08]The Compass
[00:33.66]The ancient Chinese noticed
[00:34.96]that certain kinds of metals,
[00:36.95]like iron ore, usually aligned themselves
[00:39.39]in a north to south position.
[00:41.84]By the third century,
[00:43.17]they had started making the first,
[00:44.84]simple compassesby floating small pins
[00:47.92]of magnetic metal in bowls of water.
[00:50.74]By the eleventh century,
[00:52.11]the Chinese were using sophisticated
[00:54.05]compasses to navigate their ships at sea.
[00:57.90]In the West magnetism was not discovered
[01:00.42]until the fifteenth century.
[01:02.65]Until this time, European sailors
[01:04.83]were still navigating by the stars.
[01:06.56]
