[al:新概念英语（四）] [ar:MP3 同步字幕版（美音）] [ti:Bird Flight] [by:更多学习内容，请到yingyu.chazidian.com搜索“新概念”] [00:01.00]Lesson 23 [00:02.98]Bird flight [00:10.52]What are the two main types of bird flight described by the author? [00:17.99]No two sorts of birds practise quite the same sort of flight; [00:23.47]the varieties are infinite; but two classes may be roughly seen. [00:29.45]Any ship that crosses the Pacific [00:31.59]is accompanied for many days by the smaller albatross, [00:36.85]which may keep company with the vessel for an hour [00:40.10]without visible or more than occasional movement of wing. [00:45.71]The currents of air that the walls of the ship direct upwards, [00:50.11]as well as in the line of its course, [00:53.78]are enough to give the great bird with its immense wings [00:57.45]sufficient sustenance and progress. [01:00.84]The albatross is the king of the gliders, [01:04.30]the class of fliers which harness the air to their purpose, [01:08.22]but must yield to its opposition. [01:11.61]In the contrary school, the duck is supreme. [01:16.22]It comes nearer to the engines with which man has 'conquered' the air, as he boasts. [01:22.79]Duck, and like them the pigeons, are endowed with steel-like muscles, [01:30.24]that are a good part of the weight of the bird, [01:33.32]and these will ply the short wings with such irresistible power [01:38.48]that they can bore for long distances through an opposing gale [01:43.04]before exhaustion follows. [01:45.74]Their humbler followers, such as partridges, [01:49.64]have a like power of strong propulsion, but soon tire. [01:54.30]You may pick them up in utter exhaustion, [01:57.52]if wind over the sea has driven them to a long journey. [02:01.78]The swallow shares the virtues of both schools in highest measure. [02:06.53]It tires not, nor does it boast of its power; but belongs to the air [02:13.01]travelling it may be six thousand miles to and from its northern nesting home, [02:18.95]feeding its flown young as it flies, and slipping through a medium [02:23.37]that seems to help its passage even when the wind is adverse. [02:28.78]Such birds do us good, [02:30.91]though we no longer take omens from their flight on this side and that; [02:36.29]and even the most superstitious villagers no longer take off their hats to the magpie and wish it good-morning.