没有两种鸟类的飞行方式是完全相同的；飞行形式无穷无尽；但大致可以看出两个类别。
No two sorts of birds practise quite the same sort of flight; the varieties are infinite; but two classes may be roughly seen.
任何横渡太平洋的船只都会被体型较小的信天翁伴飞许多天，这种鸟有时能跟随船只长达一小时，翅膀却没有可见的或超过偶尔一动的动作。
Any ship 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.
船体侧壁引导向上偏转的气流，以及沿航线方向的气流，足以为这只翼展宽大的巨鸟提供充足的支撑力和前进动力。
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.
信天翁是滑翔者中的王者，是那类能够驾驭气流为己所用、却又不得不向气流的阻力屈服的飞行者的代表。
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.
在另一个截然相反的流派中，鸭子是至高无上的。
In the contrary school, the duck is supreme.
它更接近于那种人类——依照他自己的夸口——已经"征服"了空中的发动机。
It comes nearer to the engines with which man has 'conquered' the air, as he boasts.
鸭子，以及与它们相似的鸽子，天生具有钢铁般的肌肉，这些肌肉占鸟体重的相当大一部分，它们将以如此不可阻挡的力量拍打那短小的翅膀，以至于这些鸟能在筋疲力尽之前，穿越对面扑来的狂风飞行很远的距离。
Duck, and like them the pigeons, are endowed with steel-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.
它们（鸭子和鸽子）更为低微的追随者，例如鹌鹑之类的鸟，具有同样强劲的推进力，但很快就会疲惫。
Their humbler followers, such as partridges, have a like power of strong propulsion, but soon tire.
如果海上的风迫使它们踏上一段漫长的旅程，你可以将它们（从地上）拾起，因为它们已精疲力竭到了极点。
You may pick them up in utter exhaustion, if wind over the sea has driven them to a long journey.
燕子在最高程度上兼具两个流派的优点。
The swallow shares the virtues of both schools in highest measure.
它从不疲倦，也不夸耀自己的能力；而是属于天空的，在往返北方筑巢之家的可能长达六千英里的旅程中飞翔，在飞翔时哺育已学会飞翔的幼鸟，悄然穿越一种似乎在帮助它前行的介质，即便逆风也不例外。
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 a medium that seems to help its passage even when the wind is adverse.
这样的鸟对我们大有裨益，尽管我们不再从它们忽左忽右的飞行中占卜吉凶；甚至连最迷信的村民也不再向喜鹊脱帽致意、道声早安了。
Such birds do us good, though 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.