>57 Lighthouses
      The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony in 1716 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by "light dues" levied on ships, the original beacon was blown up in 1776. By then there were only a dozen or so true lighthouses in the colonies. Little over a century later, there were 700 lighthouses.
      The first light erected on the West Coast in the 1850's featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were built on rocky eminences, enormous towers were not the rule. Some were made of stone and brick, others of wood or metal. Some stood on pilings or stilts; some were fastened to rock with iron rods. Farther south, from Maryland through the Florida Keys, the coast was low and sandy. It was often necessary to build tall towers there - massive structures like the majestic Cape Hatteras, North Carolina, lighthouse, which was lit in 1870. At190 feet, it is the tallest brick lighthouse in the country.
      Notwithstanding differences in appearance and construction, most American lighthouses shared several features: a light, living quarters and sometimes a bell (or later, a foghorn).They also had something else in common: a keeper and, usually, the keeper's family. The keeper's essential task was trimming the lantern wick in order to maintain a steady, bright flame. The earliest keepers came from every walk of life - they were seamen, farmers, mechanics, rough mill hands - and appointments were often handed out by local customs commissioners as political plums. After the administration of lighthouses was taken over in 1852 by the United States Lighthouse Board, an agency of the Treasury Department, the keeper corps gradually became highly professional.

      灯塔
      在新大陆上，最初的航标灯要算那些挂在港湾入口的提灯了吧。 最初的灯塔是1716 年由马萨诸塞湾殖民地在波士顿港入口一个叫小布罗斯特的岛上建起的。 这最初的灯 塔是通过向船只征收"买光钱"来维持运作的，于 1776 年被炸毁。 那时，在各殖民地，真正 的灯塔仅有十几个。 但过了一个世纪多一点，灯塔就增至七百多个了。 1850 年，在西部 沿海建起的首座灯塔基本上沿袭了新英格兰灯塔的设计方案，即那种中心或周围升起塔楼的 典型的哥德角式房子。 新英格兰与其它一些地方的灯塔在建筑风格上是多样化的。 在东北 部，灯塔大都建在石质的高地上，因此塔身不需要太高。 它们有砖石结构的； 也有木材或 金属结构的，有的灯塔建在支架上，有的则用铁条固定在岩石上。 在更南方的地区，从马 里兰到弗罗里达礁群的海岸地势低平且多为沙质，因此高大的塔身就很必要了。 例如 1870 年在北卡罗来纳的哈特拉角建的宏伟的大灯塔，高达 190 英尺，是全美最高的砖结构灯塔。 虽然美国的灯塔在外观和结构上存在一些差异，但它们确有些共同之处，比如都有灯标、有 住房、有时还有钟(后来改用雾角)。 此外，还有一个相同之处，那就是都有守塔人，通常 是守塔人全家。 守塔人的基本工作就是修剪灯蕊，以便火焰明亮而稳定。 最早的守塔人来 自各种行业：海员、农民、技工和干粗活的。 这个职位通常是作为政治回报由地方海关官 员决定任命。 但在 1852 年后，财政部下属的美国灯塔管理委员会接管了所有灯塔，守塔人 这支队伍也逐渐趋向专业化了。
>58 Animals' Compasses
      Researchers have found that migrating animals use a variety of inner compasses to help them navigate. Some steer by the position of the Sun. Others navigate by the stars. Some use the Sun as their guide during the day and then switch to star navigation by night. One study shows that the homing pigeon uses the Earth's magnetic fields as a guide in finding its way home and there are indications that various other animals from insects to mollusks, can also make use of magnetic compasses. It is of course very useful for a migrating bird to be able to switch to a magnetic compass when clouds cover the Sun; otherwise it would just have to land and wait for the Sun to come out again.
Even with the Sun or stars to steer by, the problems of navigation are more complicated than they might seem at first. For example, a worker honeybee that has found a rich source of nectar and pollen flies rapidly home to the hive to report. A naturalist has discovered that the bee scout delivers her report through a complicated dance in the hive, in which she tells the other workers not only how far away the food is, but also what direction to fly in relation to the Sun. But the Sun does not stay in one place all day. As the workers start out to gather the food, the Sun may already have changed its position in the sky somewhat. In later trips during the day, the Sun will seem to move farther and farther toward the west. Yet the worker bees seem to have no trouble at all in finding the food source. Their inner clocks tell them just where the Sun will be and they change their course correspondingly.

      动物的罗盘
      研究人员已经发现迁徙性动物可以借助各种各样的体内罗盘来校正方向。 有些动物借 助太阳的位置辨别方向，有些则依靠星星。 还有的白天利用太阳，晚上利用星星。 有研究 发现信鸽以地磁场为向导来找到回家的路。 还有迹象表明许许多多其它生物，从昆虫到软 体动物，也能利用这种磁场罗盘。 具有这种磁场罗盘，对候鸟来说当然非常有用，因为如 果乌云遮日，它可以以磁场为向导继续飞行，否则它就只好着陆，等待太阳重新出现。 即 使是借助太阳或星星导航，其中的学问也比它表面看起来的要复杂得多。 例如，一只工蜂 找到了花圃蜜园，急忙飞回蜂房报信。博物学家发现这只蜂探在蜂房里跳了一段极为复杂的 舞，通过这段舞她不但告诉其它工蜂食物有多远，而且报告了以太阳为参照的飞行路线。 但 太阳不会呆在天上不动。 当蜂群出发采食时，太阳可能已经多少改变了它在天空中的位置。 出发得越迟，太阳就越偏西，可这似乎没给寻找食物源的工蜂们带来任何不便。 它们体内 的时钟告诉他们太阳应在的位置，据此它们相应地改变前进的方向。