Lesson 23 Bird flight鸟的飞行方法First listen and then answer the following question.
What are the two main types of bird flight described by the author?
No two sorts of birds practise quite the same sort of flight; the varieties are infinite; but two classes may be roughly seen. Any shi that crosses the Pacific is accompanied for many days by the smaller albatross, Which may keep company with the vessel for an hour without visible or more than occasional movement of wing. The currents of air that the walls of the ship direct upwards, as well as in the line of its course, are enough to give the great bird with its immense wings sufficient sustenance and progress. The albatross is the king of the gliders, the class of fliers which harness the air to their purpose, but must yield to its opposition. In the contrary school, the duck is supreme. It comes nearer to the engines with which man has 'conquered' the air, as he boasts. Duck, and like them the pigeons, are endowed with such-like muscles, that are a good part of the weight of the bird, and these will ply the short wings with such irresistible power that they can bore for long distances through an opposing gale before exhaustion follows. Their humbler followers, such as partridges, have a like power of strong propulsion, but soon tire. You may pick them up in utter exhaustion, if wind over the sea has driven them to a long journey. The swallow shares the virtues of both schools in highest measure. It tires not, nor does it boast of its power; but belongs to the air, travelling it may be six thousand miles to and from its northern nesting home, feeding its flown young as it flies, and slipping through we no longer take omens from their flight on this side and that; and even the most superstitious villagers no longer take off their hats to the magpie and wish it good-morning.
没有任何两种鸟的飞行方式是相同的。鸟的飞行方式千差万别，但大体上可分为两类。任何一艘横度太平洋的轮船都会有一种小信天翁伴随飞行许多天。它们随船飞 行一小时也难得见其扇动一下翅膀。沿船体的上升的气流和沿航线向前的气流给这种巨翼大鸟以足够的浮力和推力。信天翁是滑翔飞行的鸟类之王，它能自如地驾驭 空气，但必须顺气流飞行。与滑翔鸟相对的另一类鸟中，数野鸭本领最高。它更近乎于人类自夸的“征服”了空气的发动机。野鸭及它们相似的鸽子有天赋的钢铁般 的肌肉，占了体重的很大一部分。这些肌肉以巨大的力量扇动短小的翅膀，使这类鸟能顶着大风飞行很远的路才会疲劳。次于野鸭和鸽子的鸟，如鹧鸪，有相似的巨 大推动力，但很快会疲劳。如果海风驱使它们飞行很长距离，你可以捡到一些因筋疲力尽而摔下来的鹧鸪。燕子充分兼有这两类鸟的长处，它既不疲劳，也不炫耀自 己的飞翔力；在空中十分自如，可以飞行6，000英里，可以飞往北方做窝的老家，再从老家飞回；一边飞一边喂养会飞的雏燕，甚至在顶风时也能在气流中滑 翔，似乎气流在帮它前进。这些鸟对我们是有益的，虽然我们不再从它们的飞翔姿态来占卜吉凶，连最迷信的村民也不再对喜鹊脱帽行礼，祝它早安了。
New words and expressions 生词和短语
Notes on the text课文注释
1 keep company with, 陪伴着...
2 The currents of air that the walls of the ship direct upwards,沿着船体上升的气流。
3 steel-like muscles , that are a good part of the weight of the bird,句中以that 引导的从句是一个非限定性定语从句，修饰muscles,但用that 引导非限定性定语从句是很罕见的。
4 in higest measure,最大程度地。
5 It tires not nor does it boast of its power,but belongs to the air,travelling it may be... adverse. 句中的tires not是古英语或诗歌中使用的句式。boast of 中的of = about;belong to the air的意思是：与天空融为一体。travelling it may be 是倒装语序，这是为了强调travelling的生动逼真，自然语序是it may be travelling...;nesting home意为home for nesting , flown young中的flown 意为已会飞的。a medium（媒介）指air。
Lesson 23 课后练习和答案Exercises and Answer