Book IV chapter 9

Whether the terrestrial longitude¹ can be found from the variation.

G rateful would be this work to seamen², and would bring the greatest advance to Geography. But B. Porta in chap. 38 of book 7 is mocked by a vain hope and fruitless opinion. For when he supposes that the magnetick needle would follow order and proportion in moving along meridians⁴, so that "the neerer it is to the east, the more it will decline from the Meridian³ line, toward the east; and the neerer it comes to the west, the point of the needle will decline the more to the west" (which is totally untrue), he thinks that he has discovered a true index of longitude. But he is mistaken. Nevertheless, admitting and assuming these things (as though they were perfectly⁵ true), he makes a large compass indicating degrees and minutes, by which these proportional changes of the versorium might be observed. But those very principles are false, and ill conceived, and very ill considered; for the versorium does not turn more to the east because a journey is made toward the east: and although the variation in the more westerly parts of Europe and the adjoining ocean is to the east and beyond the Azores is changed a little to the west, yet the variation is, in various ways, always uncertain, both on account of longitude and of latitude⁶, and because of the approach toward extensive tracts⁷ of land, and also because of the form of the dominant⁸ terrestrial eminences⁹; nor does it, as we have before demonstrated, follow the rule of any particular meridian. It is with the same vanity also that Livio Sanuto so greatly torments¹⁰ himself and his readers. As for the fact that the crowd of philosophizers and sailors suppose that the meridian passing through the Azores marks the limits of variation, so that on the other and opposite side of that meridian a magnetick body necessarily respects the poles exactly, which is also the opinion of Joannes Baptista Benedictus and of many other writers on navigation, it is by no means true. Stevinus (on the authority of Hugo Grotius) in his Havenfinding Art distinguishes the variation according to the meridians: "It may be seene in the Table of variations, that in Coruo the Magneticall needle pointeth due North: but after that, the more a man shal goe towards the East, so much the more also shall he see the needle varie towards the East [ἀνατολίζειν], till he come one mile to the Eastward¹¹ from Plimouth, where the variation comming to the greatest is 13 degr. 24 min. From hence the Northeasting [Anatolismus] beginneth to decrease, til you come to Helmshude (which place is Westward¹² from the North Cape¹³ of Finmark) where againe the needle pointeth due North. Now the longitude from Coruo to Helmshude is 60 degr. Which things being well weighed, it appeareth that the greatest variation [Chalyboclysis] 13 degr. 24 minutes at Plimmouth (the longitude whereof is 30 degr.) is in the midst betweene the places where the needle pointeth due North." But although this is in some part true in these places, yet it is by no means true that along the whole of the meridian of the island of Corvo the versorium looks truly to the north; nor on the meridian of Plymouth is the variation in other places 13 deg. 24 min. — nor again in other parts of the meridian of Helmshuda does it point to the true pole. For on the meridian passing through Plymouth in Latitude 60 degrees the North-easterly variation is greater: in Latitude 40 deg. much less; in Latitude 20 deg. very small indeed. On the meridian of Corvo, although there is no variation near the island, yet in Latitude 55 degrees the variation is about ½ a rumbe to the North-west; in Latitude 20 deg. the versorium inclines ¼ of a rumbe toward the East. Consequently the limits of variation are not conveniently determined¹⁴ by means of great circles and meridians, and much less are the ratios of the increment¹⁵ or decrement toward any part of the heavens properly investigated by them. Wherefore the rules of the abatement¹⁶ or augmentation of Northeasting or Northwesting, or of increasing or decreasing the magnetick deviation¹⁷, can by no means be discovered by such an artifice¹⁸. The rules which follow later for variation in southern parts of the earth investigated by the same method are altogether vain and absurd. They were put forth¹⁹ by certain Portuguese²⁰ mariners²¹, but they do not agree with the observations, and the observations themselves are admitted to be bad. But the method of haven-finding in long and distant voyages by carefully observed variation (such as was invented by Stevinus, and mentioned by Grotius) is of great moment, if only proper instruments are in readiness, by which the magnetick deviation can be ascertained²² with certainty at sea.

1 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。

2 seamen   

n.海员

参考例句：

• Experienced seamen will advise you about sailing in this weather. 有经验的海员会告诉你在这种天气下的航行情况。
• In the storm, many seamen wished they were on shore. 在暴风雨中，许多海员想，要是他们在陆地上就好了。

3 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。

4 meridians   

n.子午圈( meridian的名词复数 )；子午线；顶点；（权力，成就等的）全盛时期

参考例句：

• Meridians are great circles passing through both poles. 经线均为通过两极。 来自辞典例句
• The Cutaneous Regions are within the domains of the Twelve Regular Meridians. 十二皮部是十二经脉功能活动反映于体表的部位，也是络脉之气散布之所在。 来自互联网

5 perfectly   

adv.完美地，无可非议地，彻底地

参考例句：

• The witnesses were each perfectly certain of what they said.证人们个个对自己所说的话十分肯定。
• Everything that we're doing is all perfectly above board.我们做的每件事情都是光明正大的。

6 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。

7 tracts   

大片土地( tract的名词复数 )； 地带； （体内的）道； （尤指宣扬宗教、伦理或政治的）短文

参考例句：

• vast tracts of forest 大片大片的森林
• There are tracts of desert in Australia. 澳大利亚有大片沙漠。

8 dominant   

adj.支配的，统治的；占优势的；显性的；n.主因，要素，主要的人(或物)；显性基因

参考例句：

• The British were formerly dominant in India.英国人从前统治印度。
• She was a dominant figure in the French film industry.她在法国电影界是个举足轻重的人物。

9 eminences   

卓越( eminence的名词复数 )； 著名； 高地； 山丘

参考例句：

• Both are truly grey eminences who have become accustomed to the exercise of influence. 两个人都是真正的幕后操纵者，他们已习惯于用其影响进行幕后操纵。

10 torments   

（肉体或精神上的）折磨，痛苦( torment的名词复数 )； 造成痛苦的事物[人]

参考例句：

• He released me from my torments. 他解除了我的痛苦。
• He suffered torments from his aching teeth. 他牙痛得难受。

11 eastward   

adv.向东；adj.向东的；n.东方，东部

参考例句：

• The river here tends eastward.这条河从这里向东流。
• The crowd is heading eastward,believing that they can find gold there.人群正在向东移去，他们认为在那里可以找到黄金。

12 westward   

n.西方，西部；adj.西方的，向西的；adv.向西

参考例句：

• We live on the westward slope of the hill.我们住在这座山的西山坡。
• Explore westward or wherever.向西或到什么别的地方去勘探。

13 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。

14 determined   

adj.坚定的；有决心的

参考例句：

• I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
• He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。

15 increment   

n.增值，增价；提薪，增加工资

参考例句：

• Each increment of knowledge tells us more of our world.知识的点滴增长都会增进我们对世界的认知。
• She receives a salary increment each year.她每年得到加薪。

16 abatement   

n.减(免)税，打折扣，冲销

参考例句：

• A bag filter for dust abatement at the discharge point should be provided.在卸料地点应该装设袋滤器以消除粉尘。
• The abatement of the headache gave him a moment of rest.头痛减轻给他片刻的休息。

17 deviation   

n.背离，偏离；偏差，偏向；离题

参考例句：

• Deviation from this rule are very rare.很少有违反这条规则的。
• Any deviation from the party's faith is seen as betrayal.任何对党的信仰的偏离被视作背叛。

18 artifice   

n.妙计，高明的手段；狡诈，诡计

参考例句：

• The use of mirrors in a room is an artifice to make the room look larger.利用镜子装饰房间是使房间显得大一点的巧妙办法。
• He displayed a great deal of artifice in decorating his new house.他在布置新房子中表现出富有的技巧。

19 forth   

adv.向前；向外，往外

参考例句：

• The wind moved the trees gently back and forth.风吹得树轻轻地来回摇晃。
• He gave forth a series of works in rapid succession.他很快连续发表了一系列的作品。

20 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。

21 mariners   

海员，水手（mariner的复数形式）

参考例句：

• Mariners were also able to fix their latitude by using an instrument called astrolabe. 海员们还可使用星盘这种仪器确定纬度。
• The ancient mariners traversed the sea. 古代的海员漂洋过海。

22 ascertained   

v.弄清，确定，查明( ascertain的过去式和过去分词 )

参考例句：

• The previously unidentified objects have now been definitely ascertained as being satellites. 原来所说的不明飞行物现在已证实是卫星。 来自《简明英汉词典》
• I ascertained that she was dead. 我断定她已经死了。 来自《简明英汉词典》