(
课件网) Reading A compass consists of a small magnet balanced on a point so that it can move round in a circle. The magnet is generally called a needle because it is shaped like a needle. One end of the needle is often marked “N” for north, or coloured in some way to indicate that it points toward north. astrolabe The astrolabe measures the height and position of the sun. If you can measure this accurately, a sailor can tell how many degrees the boat is from the North Pole. From this he can tell where the boat is in the ocean. 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. quadrant nautical chart Zheng He’s Voyage Zheng He’s Voyage 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. Discuss 1. How do you think seamen found their way before modern accurate methods of navigation were invented? Kept close to the shore, used nature such as the sun, wind, birds, tide, etc, to help them, and used some of the instruments including a compass, astrolabe, etc. 2. Which do you think was easier to work out: latitude or longitude? Latitude, because it was used to measure how far you had traveled from land on a straight line. It was discovered a long time before longitude. 3. Can you identify these early navigational instruments seamen used and explain how they are used? 1) compass ( in ancient China) 2) astrolabe 3) sextant 4) sea / nautical / marine chart 4. Which ones do you think are still used today? Sea charts are still used today. Language points on P14 1. course n. 过程, 经过, 进程, 方针, 路线, 跑道, 课程, 一道菜 Tom made much noise in the course of discussion. 在讨论期间汤姆弄出了很大的响声。 The ship was blown off course. 那船被吹离了航向。 We made three courses: soup, meat and vegetables, and fruit. 我们有三道菜: 汤, 肉和蔬菜, 还有水果。 Phrases with “course” in course of 正在……过程中, 在……期间 in due course = at the proper or right time 在合适或正好的时间 of course ① in the natural or expected order of things; naturally. 按事物自然的或预期的顺序;自然地 2. aim n.目标, 目的, 瞄准 v ... ...
