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38 经度线的探索及其对安全航海的作用
DATE=6-20-01
TITLE=EXPLORATIONS #1957 - Longitude1
BYLINE=Oliver Chanler
VOICE ONE:
This is Steve Ember.
VOICE TWO:
And this is Bob Doughty2 with the VOA Special English program EXPLORATIONS. Today, we tell about how people learned an important piece of information necessary for safely sailing on the oceans. It is called longitude.
(((THEME)))
VOICE ONE:
On a foggy October night in Seventeen-Oh-Seven, four English (1) navy ships hit rocks in the Atlantic Ocean and sank. Two-thousand men (2) drowned. The ships had been sailing in the thick fog for twelve days. There was no sure way to know where they were. The commander of the ships had been worried that they could hit rocks if they were not careful. He asked his (3) navigators for their opinion on their location in the ocean
. The navigators did not really know. They told the commander they thought they were west of a small island near the coast of northwestern France
. They were wrong. Instead, they sailed onto rocks near a small group of islands southwest of England's Atlantic coast. The navigators' lack of knowledge led to the loss of four ships and two-thousand lives.
VOICE TWO:
When people began sailing out of sight of land, sailors did not know how to tell where they were on the open sea. Land travelers can look at a mountain, a river, or an object that shows them where they are in relation to where they came from. On the ocean, however, there is no sign to tell a sailor where he is
. The most important device for knowing directions on the ocean is a (4) compass. A compass is a (5) device containing a metal object that points toward the (6) magnetic north pole. This shows navigators the direction of north, and therefore also south, east, and west. But sailors need more information to sail safely on the open sea.
VOICE ONE:
Most maps of the world show lines that are not on the Earth's surface. One line is the equator. It is an (7) imaginary line around the widest part of the Earth. There are similar lines both north and south of the (8) equator. These circles become smaller and smaller toward the north pole and the south pole.
These lines, or circles, are (9) parallel - meaning that they are equally distant from each other at any point around the world. These lines show what is called (10) latitude3.
A navigator can know the latitude of his ship by observing the location of stars, where the sun rises in the morning and sets in the evening, and what time of year it is. With this information he knows where his ship is in relation to the north or south pole and the equator.
VOICE TWO:
Still, there is one more important piece of information necessary for safely sailing the oceans. For many centuries, scientists, (11) astronomers5 and inventors searched for a way to tell longitude. The lines of (12) longitude go the other way from latitude lines. They stretch from the north pole to the south pole, and back again in great circles of the same size. All of the lines of longitude meet at the top and bottom of the world.
In her book, Longitude, writer Dava Sobel tells the story about longitude and how the problem of knowing it was solved
. ((MUSIC BRIDGE))
VOICE ONE:
For centuries, the great scientists of the world struggled to develop a way to learn longitude. To learn longitude at any place requires knowledge about time. A navigator needs to know what time it is on his ship and also the time at another place of known longitude - at the very same moment.
The Earth takes twenty-four hours to complete one full turn or (13) revolution of three-hundred-sixty degrees. One hour marks one twenty-fourth of a turn, or fifteen degrees. So each hour's time difference between the ship and the starting point marks a ship's progress of fifteen degrees of longitude to the east or west. Those fifteen degrees of longitude mark a distance traveled.
At the equator, where the Earth is widest, fifteen degrees (14) stretches about one-thousand-six-hundred kilometers. North or south of that line, however, the distance value of each degree (15) decreases. One degree of longitude equals four minutes of time all around the world. But in measuring distance, one degree (16) shrinks from about one-hundred-nine kilometers at the Equator to nothing at the north and south poles.
VOICE TWO:
For many centuries, navigators hoped they could find longitude by observing the movement of stars at night. During the day, the sun provided information about the time on a ship, and its direction. However, it did not provide necessary information about the time somewhere else. In the Sixteenth century, one astronomer4 suggested that navigators could observe the moon as it passed in front of different known stars to tell longitude. But, there was not enough information about the stars to use this method (17) effectively. Astronomers could not tell exactly where the moon would be from one night or day to the next.
Yet it seemed to those seeking to solve the longitude problem that the only solution was in the moon and stars.
((MUSIC BRIDGE))
VOICE ONE:
During the Seventeenth Century, English astronomers began a major effort to map the stars and their relationship to the moon as it passed across the sky. Royal Astronomer John Flamsteed worked at this task for forty years. The next Royal Astronomer, Edmund Halley, spent another forty years gathering6 information about the moon's (18) orbit.
After many years of gathering the necessary information, it became possible to learn longitude by observing the stars and the moon. In Seventeen-Sixty- Six, Royal Astronomer Nevil Maskelyne published the (19) Nautical7 Almanac and Astronomical8 (20) Ephemeris.
It contained all the necessary information about the moon and stars that sailors would need to help them learn their longitude.
This new method was not simple. A navigator had to use complex observing (21) instruments to note the position of the moon and stars. Then he had to seek the correct information in the Nautical Almanac about the moon and stars at that time of night or day. The final step in the process was to take the mathematical information from the book, link it to the current information and solve the resulting problem. This took an average of four hours to do. VOICE TWO:
While scientists were studying the stars and moon to solve the longitude problem, a man named John Harrison was working on another project. He was trying to build a clock that would help sailors learn longitude. His task also was difficult and complex. Mister Harrison had to develop a clock that was not affected9 by the movement of a ship on the ocean or changes in temperature or (22) atmospheric10 pressure.
He began developing his clock in Seventeen-Thirty. It took five years to complete. The complex device weighed thirty-four kilograms. Several years later, Mister Harrison built a second clock. It was smaller, but weighed more than the first. Mister Harrison was not satisfied and began work on another device.
Twenty years, later he completed a device that was smaller than the first two, and weighed less. But, still Mister Harrison was not satisfied.
Two years later, in Seventeen-Fifty-Seven, he produced a small clock that he could hold in his hand. The clock could tell the correct time in two places, meeting the requirements for learning longitude on the sea.
VOICE ONE:
For many years after Mister Harrison's work was completed, the idea of using a clock to learn longitude was rejected. However, that opinion changed when (23) manufacturers learned how to make better and less costly11 (24) versions of Mister Harrison's clocks. The clocks became known as (25) chronometers12. By Eighteen- Fifteen, five-thousand chronometers were in use on ships sailing the world's oceans. The complex documents and mathematical work were no longer necessary. Almost any sailor could tell what his longitude was by simply looking at a clock. The world had changed.
VOICE TWO:
John Harrison's clocks can be seen today at the Old Royal (26) Observatory13 in (27) Greenwich, England. The first three are still operating, showing the correct time. To look at them is to see the simple solution to a problem that worried people for many centuries. Today, the solution to the problem is so common that it is difficult to understand that there was a problem at all.
(((THEME)))
VOICE ONE:
This program was written by Oliver Chanler and produced by Paul Thompson. This is Steve Ember.
VOICE TWO:
And this is Bob Doughty. Join us again next week for EXPLORATIONS, a program in Special English on the Voice of America.
(1) navy [ `neivi] n.海军
(2) drown [draUn] vt.淹没
(3) navigator [`nAvigeit[] n.航海家
(4) compass [`kQmpEs] n.指南针
(5) device [di`vais] n. 设备
(6) magnetic north pole 磁北极
(7) imaginary [i`mAdVinEri] adj.假想的, 想象的, 虚构的
(8) equator [i`kweitE]n.赤道, 赤道似的圈.圆
(9) parallel [`pArElel] adj.平行的
(10) latitude [`lAtitjU:d] n.纬度, 范围, (用复数)地区, 行动或言论的自由(范围)
(11) astronomer [E`strRnEmE] n.天文学家
(12) longitude [`lRndVitjU:d] n.经度, 经线
(13) revolution [9rev[`lUF[n] n.旋转
(14) stretch [stretF] v.伸展, 伸长
(15) decrease [di:`kri:s] v.减少
(16) shrink [FriNk] v.收缩, (使)皱缩, 缩短
(17) effectively [i`fektivli] adv.有效地, 有力地
(18) orbit [ `C:bit] n.轨道
(19) nautical almanac 航海天文年历
(20) ephemeris [i`femEris] n.[天]星历表, 历书, 短命的东西
(21) instrument [`instrUm[nt] n.工具, 手段, 器械, 器具, 手段
(22) atmospheric pressure n.大气压力
(23) manufacturer [9mAnjU`fAktFErE] n.制造业者, 厂商
(24) version [ `v[:FEn] n.版本
(25) chronometer [krE`nRmit[] n.记时计
(26) observatory [Eb`zE:v[t[ri] n.天文台, 气象台
(27) Greenwich [`grinidV] n.格林威治(位于英国伦敦东南部,为本初子午线所经之地,原设有英国皇家格林威治天文台)
收听单词发音 |
1
longitude
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| n.经线，经度 | |
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2
doughty
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| adj.勇猛的，坚强的 | |
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3
latitude
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| n.纬度，行动或言论的自由(范围)，(pl.)地区 | |
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4
astronomer
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| n.天文学家 | |
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5
astronomers
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| n.天文学者，天文学家( astronomer的名词复数 ) | |
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6
gathering
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| n.集会，聚会，聚集 | |
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7
nautical
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| adj.海上的，航海的，船员的 | |
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8
astronomical
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| adj.天文学的，（数字）极大的 | |
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9
affected
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| adj.不自然的，假装的 | |
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10
atmospheric
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| adj.大气的，空气的；大气层的；大气所引起的 | |
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11
costly
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| adj.昂贵的，价值高的，豪华的 | |
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12
chronometers
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| n.精密计时器，航行表( chronometer的名词复数 ) | |
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13
observatory
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| n.天文台，气象台，瞭望台，观测台 | |
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