| GWD-26-Q32-Q35 中国人改进了英国人测量珠峰高度的方法 |
|
| In 1975 Chinese survey teams |
| remeasured Mount Everest, the highest |
| of the Himalayan mountains. Like the |
|
| Line British in 1852, they used the age-old |
| (5) technique of “carrying in” sea level: |
| surveyors marched inland from the |
| coast for thousands of miles, stopping |
| at increments of as little as a few feet |
| to measure their elevation, and mark- |
| (10) ing each increment with two poles. |
| To measure the difference in elevation |
| between poles, surveyors used an |
| optical level—a telescope on a level |
| base—placed halfway between the |
| (15) poles. They sighted each pole, read- |
| ing off measurements that were then |
| used to calculate the change in eleva- |
| tion over each increment. In sight of |
| the peaks the used theodolitesn.经纬仪— |
| (20) telescopes for measuring vertical and |
| horizontal angles—to determine the |
| elevation of the summit. |
| The Chinese, however, made |
| efforts to correct for the errors that |
| (25) had plagued the British. One source |
| of error is refraction折射, the bending of |
| light beams as they pass through air |
| layers of different temperature and |
| pressure. Because light traveling. |
| (30) down from a summit passes through |
| many such layers, a surveyor could |
| sight a mirage rather than the peak |
| itself. To reduce refraction errors, the |
| Chinese team carried in sea level to |
| (35) within five to twelve miles of Everest’s |
| summit, decreasing the amount of air |
| that light passed through on its way to |
| their theodolites. The Chinese also |
| launched weather balloons near their |
| (40) theodolites to measure atmospheric |
| temperature and pressure changes |
| to better estimate refraction errors. |
| Another hurdle is the peak’s shape. |
| When surveyors sight the summit. |
| (45) there is a risk they might not all |
| measure the same point. In 1975 |
| the Chinese installed the first survey |
| beacon灯塔 on Everest, a red reflector |
| visible through a theodolite for ten |
| (50) miles, as a reference point. One |
| more source of error is the uneven- |
| ness of sea level. The British |
| assumed that carrying in sea level |
| would extend an imaginary line from |
| (55) the shore along Earth’s curve to a |
| point beneath the Himalaya. In |
| reality, sea level varies according |
| to the irregular interior of the planet. |
| The Chinese used a gravity meter to |
| correct for local deviations in sea level. |
| ------------------------------------------------------------- |
| Q32 |
| It can be inferred from the passage that refraction would be most likely to cause errors in measurements of a mountain’s elevation under which of the following conditions? |
| A. When there are local variations in sea level |
| B. When light passes through humid air |
| C. When theodolites are used relatively far from the mountain peak. |
| D. When weather balloons indicate low air temperature and pressure. |
|
| E. When sea level has been carried in to within five to twelve miles of the summit. |
GWD的答案是：D |
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发表于 2007-11-6 20:57:00
