高中英语 Sailing the oceans-Reading课件 新人教版选修9 课件VIP免费

ReadingThe four basic instruments for navigation: Sinan, Inch Astrolabe, Sextant and nautical map.Sinan, the ancient Chinese compass. It was invented by Zhang Heng in the Han dynasty. It is made up of a bronze foundation ( 青铜地盘 ) and magnetic spoon( 磁勺 ) which is made of natural magnet, positioned right in the central of the foundation. It was invented by Zhang Heng in the Han dynasty. It is made up of a bronze foundation ( 青铜地盘 ) 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 ). 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.astrolabeastrolabesextantThe 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 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 ...