Unit3 Section Ⅰ Reading，Listening and Thinking（教师用书word）-2022-2023学年新教材高中英语选择性必修第四册【精讲精练】人教版

当今航行技术达到前所未有的水平，那么你知道古代一些有关航海方面的仪器吗？ Sinan, the ancient Chinese compass It was invented by Zhang Heng in the Han dynasty.It is made up of a bronze foundation and magnetic spoon(磁勺) which is made of natural magnet, positioned right in the central of the foundation. The handle of the spoon points to the south, while the other side points to the north.When the Sinan is in the still, the handle of the spoon points to the south because of influence of the terrestrial magnetism(地磁). Astrolabe It has 17 stars listed as well as a map of the sky overhead (for 37 degrees) and the ecliptic(黄道).The time of day or night is on the outside edge with noon at the top of the Astrolabe and midnight at the bottom.It comes with a carrying chain, a pouch, and a book on its use.The reverse side has a sight for measuring the elevations of the heavenly bodies. Sextant The sextant is a navigational instrument for measuring the angle between the horizon and some object in the sky.First a sailor looks at the horizon through an eyepiece.At the same time he can see light from the sun or a star reflected off a small mirror on top of the instrument, onto a second mirror and into the eyepiece. The navigator can then see two images, the horizon and the sun side by side.He can then measure the angle between them on a scale at the bottom of the instrument.The scale goes from 0 to 120 degrees.An earlier instrument, called a quadrant, measured in angle in the same way but it could only measure angles from 0 to 90 degrees. Nautical chart Nautical charts are maps of the depth of the sea and the currents of the oceans.They provide modern sailors with routes through the seas, rather like roads through the countryside.The information began to be collected in the nineteenth century and has continued to be updated ever since.These charts were not available to Captain Bligh or Zheng He. 根据短文内容回答问题： 1．What is the theory of the Sinan invented by Zhang Heng?