Book IV chapter 15

The variation of the magnetick needle in the great Æthiopick and American sea, beyond the æquator.

D iscourse hath already been had of the mode and reason of the variation in the great Atlantick Ocean: but when one has advanced beyond the æquator off the east coast of Brazil the magnetick needle turns aside toward the mainland, namely, with that end of it which points to the south; so that with that end of the versorium it deviates¹ from the true meridian² toward the west; which navigators observe at the other end and suppose a variation to occur toward the east. But throughout the whole way from the first promontory³ on the east of Brazil, by Cape⁴ St. Augustine and thence to Cape Frio, and further still to the mouth of the Strait of Magellan, the variation is always from the south toward the west with that end of the versorium which tends toward the antarctick pole. For it is always with the accordant end that it turns toward a continent. The variation, however, occurs not only on the coast itself, but at some distance from land, such as a space of fifty or sixty German miles or even more. But when at length one has progressed far from land, then the arc begins to diminish: for the magnetick needle turns aside the less toward what is too far off, and is turned aside the less from what is present and at hand, since it enjoys what is present. In the Island of St. Helena (the longitude⁵ of which is less than is commonly marked on charts and globes) the versorium varies by one degree or nearly two. The Portuguese⁶ and others taught by them, who navigate⁷ beyond the Cape of Good Hope to the Indies, set a course toward the Islands of Tristan d'Acunha, in order that they may enjoy more favourable⁸ winds; in the former part of their course the change of variation is not great; but after they have approached the islands the variation increases; and close to the islands it is greater than anywhere else in the whole course. For the end of the versorium tending to the south (in which lies the greatest source of the variation) is caught and allured⁹ toward the south-west by the great promontory of the southern land. But when they proceed onward¹⁰ toward the Cape of Good Hope the variation diminishes the more they approach it. But on the prime meridian in the latitude¹¹ of 45 degrees, the versorium tends to the south-east: and one who navigates¹² near the coast from Manicongo to the tropick, and a little beyond, will perceive that the versorium tends from the south to the east, although not much. At the promontory of Agulhas it preserves slightly the variation which it showed near the islands of d'Acunha, which nevertheless is very much diminished because of the greater remoteness from the cause of variation, and consequently there the southern end of the versorium does not yet face exactly to the pole.

1 deviates   

v.偏离，越轨( deviate的第三人称单数 )

参考例句：

• The boy's behavior deviates from the usual pattern. 这个男孩子的举止与一般人不同。 来自《简明英汉词典》
• The limit occurs when the ordinate deviates appreciably from unity. 这个限度发生在纵坐标明显地从单位1偏离的时候。 来自辞典例句

2 meridian   

adj.子午线的；全盛期的

参考例句：

• All places on the same meridian have the same longitude.在同一子午线上的地方都有相同的经度。
• He is now at the meridian of his intellectual power.他现在正值智力全盛期。

3 promontory   

n.海角；岬

参考例句：

• Genius is a promontory jutting out of the infinite.天才是茫茫大地突出的岬角。
• On the map that promontory looks like a nose,naughtily turned up.从地图上面，那个海角就像一只调皮地翘起来的鼻子。

4 cape   

n.海角，岬；披肩，短披风

参考例句：

• I long for a trip to the Cape of Good Hope.我渴望到好望角去旅行。
• She was wearing a cape over her dress.她在外套上披着一件披肩。

5 longitude   

n.经线，经度

参考例句：

• The city is at longitude 21°east.这个城市位于东经21度。
• He noted the latitude and longitude,then made a mark on the admiralty chart.他记下纬度和经度，然后在航海图上做了个标记。

6 Portuguese   

n.葡萄牙人；葡萄牙语

参考例句：

• They styled their house in the Portuguese manner.他们仿照葡萄牙的风格设计自己的房子。
• Her family is Portuguese in origin.她的家族是葡萄牙血统。

7 navigate   

v.航行，飞行；导航，领航

参考例句：

• He was the first man to navigate the Atlantic by air.他是第一个飞越大西洋的人。
• Such boats can navigate on the Nile.这种船可以在尼罗河上航行。

8 favourable   

adj.赞成的，称赞的，有利的，良好的，顺利的

参考例句：

• The company will lend you money on very favourable terms.这家公司将以非常优惠的条件借钱给你。
• We found that most people are favourable to the idea.我们发现大多数人同意这个意见。

9 allured   

诱引，吸引( allure的过去式和过去分词 )

参考例句：

• They allured her into a snare. 他们诱她落入圈套。
• Many settlers were allured by promises of easy wealth. 很多安家落户的人都是受了诱惑，以为转眼就能发财而来的。

10 onward   

adj.向前的，前进的；adv.向前，前进，在先

参考例句：

• The Yellow River surges onward like ten thousand horses galloping.黄河以万马奔腾之势滚滚向前。
• He followed in the steps of forerunners and marched onward.他跟随着先辈的足迹前进。

11 latitude   

n.纬度，行动或言论的自由(范围)，(pl.)地区

参考例句：

• The latitude of the island is 20 degrees south.该岛的纬度是南纬20度。
• The two cities are at approximately the same latitude.这两个城市差不多位于同一纬度上。

12 navigates   

v.给（船舶、飞机等）引航，导航( navigate的第三人称单数 )；（从海上、空中等）横越；横渡；飞跃

参考例句：

• Dolpins also navigates by some kind of echo system. 原来海豚也是借助某种回声系统寻向的。 来自辞典例句
• Navigates in menus, lists, choice screens and into edited texts. 可以操纵菜单、列表、屏幕选项和进入编辑文本。 来自互联网