发布时间 : 星期六 文章选修9 课文与翻译更新完毕开始阅读
Certain tides and currents could be used by skillful sailors to carry ships to their destination.These skills helped sailors explore the seas and discover new lands. They increased their ability to navigate new seas when they used instruments.
第一页：
借助大自然使船只沿海岸线行驶
这似乎是最早的、最有用的探险(exploration)方式,所冒的风险也最小。
利用天体(celestial bodies) ●北极星
在北极, 北极星是在天上的最高位置；而在赤道(equator)上，北极星却在地平线(horizon)上。因此，熟练的航海探险家就能够利用北极星来确定他们自己的位置。 ●太阳
在晴朗的日子里，特别是夏天，船员可以利用正午在头顶上(overhead)的太阳来导航。他们可以利用太阳的高度来计算出他们自己的位置。 ●云层
海上的船长观测岛上的云层。有一种特殊的云彩的形状表明附近有陆地。
利用野生动植物 ●海藻
海员常常看到海里的海藻，并能根据它的颜色和气味判断这种海藻在那儿有多久了。如果它颜色新鲜而且气味浓烈,那说明船只就离陆
地很近了。 ●鸟
在看不见陆地的时候, 可以用海鸟来指明通往陆地的去路。在夜晚的时候, 筑巢而居的鸟就要返回陆地鸟窝。因此, 即使在远离海岸的大洋上, 海员们也可以跟随这些鸟儿到达陆地。 利用天气 ●雾
正如雾气汇聚在溪流或江河上一样, 雾气也能汇聚在海洋上。当靠近陆地时, 海员们可以用雾气来帮助确定溪流或江河的位置。 ●风
聪明的海员常常利用风向来导航。风向可以使船只加快速度，也可以造成危险。于是，北欧的海盗们在出海或返航时都要观察风向。 利用大海
技术娴熟的海员可以利用大海的某些潮汐(tides)或浪潮把船送往他们的目的地。 Page 2:
Using navigational instruments to help Finding longitude
There was no secure method of measuring longitude until the 17th century when the British solved this theoretical problem. Nobody knew that the earth moved westwards 15 degrees every hour, but sailors did know an approximate method of calculating longitude using speed and time. An early method of measuring speed involved throwing a knotted rope tied to a
log over the side of the ship. The rope was tied to a log which was then thrown into the sea. As the ship advanced through the water the knots were counted as they passed through a seaman's hands. The number of knots that were counted during a fixed period of time gave the speed of the ship in nautical miles per hour. 第二页： 利用航海工具 找出经度
直到 17 世纪英国人解决了这个理论问题后,人们才有了测量经度的可靠方法 。以前没有人知道地球每小时向东转动约15度，然而海员们确实知道用速度和时间来计算经度的近似标准的方法。早期测量速度的方法是沿着船边拉一根打结的(knotted)绳子，把这根绳子系在一根圆木(log)上，然后把它抛入海里。当船只在水中前进时，这些绳结从海员的手中通过, 这时海员就记下绳结的数目。在一定时间内计算出有多少个结, 就可以算出船只每小时航行多少海里(nautical miles)的速度。
Later, when seamen began to use the compass in the 12th century they could calculate longitude using complicated mathematical tables. The compass has a special magnetic pointer which always indicates the North Pole, so it is used to help find the direction that the ship needs to go. In this way the ship could set a straight course even in the middle of the ocean. 后来, 当12世纪海员们开始使用指南针的时候, 他们就可以用复杂的数学表来计算出经度了。指南针有一个特殊的磁针(magnetic), 始终
指着北极。因此人们用它来帮助找出船只所要去的方向。这样, 即使在大海中船只也可以直线航行。 Finding latitude The Bearing Circle
It was the first instrument to measure the sun's position. A seaman would measure the sun's shadow and compare it with the height of the sun at midday. Then he could tell if he was sailing on his correct rather than a random course. 找出纬度(latitude)
●方位圆
这是最早用来测量太阳位置的工具。海员可以测量太阳的影子，并把它同太阳在正午时的高度作比较，这样就可以知道自己是在正确的航道上或是在随意行驶。 A Bearing Circle The Astrolabe
The astrolabe, quadrant and sextant are all connected. They are developments of one another. The earliest, the astrolabe, was a special all-in-one tool for telling the position of the ship in relation to the sun and various stars which covered the whole sky. This gave the seamen the local time and allowed them to find their latitude at sea. However, it was awkward to use as one of the points of reference was the moving ship itself. ●星盘
星盘、象限仪和六分仪相互都有联系。它们是在彼此的基础上发