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Book V chapter 2
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Declinations of the magnetick needle.

Diagram of declinations of the magnetick needle, when excited, in the various portions of the sphere, and horizons of the earth, in which there is no variation of the declination.

As æquator let A B be taken, C the north pole, D the south, E G dipping-needles in the northern, H F in the southern part of the earth or of a terrella. In the diagram before us all the cusps have been touched by the true Arctick pole of the terrella.

Here we have the level position of the magnetick needle on the æquator of the earth and the stone, at A and B, and its perpendicular1 position at C, D, the poles; whilst at the places midway between, at a distance of 45 degrees, the crosses of the needle dip toward the south, but the cusps just as much toward the north. Of which thing the reason will become clear from the demonstrations2 that follow.

Declinations of the magnetick needle.

Diagram of the rotation3 and declination of a terrella conforming to the globe of the earth, for a latitude4 of 50 degrees north.

A is the boreal pole of the earth or of a rather large terrella, B the southern, C a smaller terrella, E the southern pole of the smaller terrella, dipping in the northern regions233. The centre C is placed on the surface of the larger terrella, because the smaller terrella shows some variation on account of the length of the axis5; inappreciable, however, on the earth. Just as a magnetick needle dips in a regional latitude of 50 degrees, so also the axis of a stone (of a spherical6 stone, of course) is depressed7 below the horizon, and its natural austral pole falls, and its boreal pole is raised on the south toward the Zenith. In the same way also a circular disc of iron behaves, which has been carefully touched at opposite parts on its circumference8; but the magnetical experiments are less clear on account of the feebler forces in round pieces of iron.

spikes9." alt="Variety in the declinations of iron spikes." src="https://ebooks.adelaide.edu.au/g/gilbert/william/on-the-magnet/figures/illo179.jpg" />

Variety in the declinations of iron spikes at various latitudes10 of a terrella.

The declination of a magnetick needle above a terrella is shown by means of several equal iron wires, of the length of a barleycorn, arranged along a meridian11. The wires on the æquator are directed by the virtue12 of the stone toward the poles, and lie down upon its body along the plane of its horizon. The nearer they are brought to the poles, the more they are raised up by their versatory nature. At the poles themselves they point perpendicularly13 toward the very centre. But iron spikes, if they are of more than a due length, are not raised straight up except on a vigorous stone.


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1 perpendicular GApy0     
adj.垂直的,直立的;n.垂直线,垂直的位置
参考例句:
  • The two lines of bones are set perpendicular to one another.这两排骨头相互垂直。
  • The wall is out of the perpendicular.这墙有些倾斜。
2 demonstrations 0922be6a2a3be4bdbebd28c620ab8f2d     
证明( demonstration的名词复数 ); 表明; 表达; 游行示威
参考例句:
  • Lectures will be interspersed with practical demonstrations. 讲课中将不时插入实际示范。
  • The new military government has banned strikes and demonstrations. 新的军人政府禁止罢工和示威活动。
3 rotation LXmxE     
n.旋转;循环,轮流
参考例句:
  • Crop rotation helps prevent soil erosion.农作物轮作有助于防止水土流失。
  • The workers in this workshop do day and night shifts in weekly rotation.这个车间的工人上白班和上夜班每周轮换一次。
4 latitude i23xV     
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。
5 axis sdXyz     
n.轴,轴线,中心线;坐标轴,基准线
参考例句:
  • The earth's axis is the line between the North and South Poles.地轴是南北极之间的线。
  • The axis of a circle is its diameter.圆的轴线是其直径。
6 spherical 7FqzQ     
adj.球形的;球面的
参考例句:
  • The Earth is a nearly spherical planet.地球是一个近似球体的行星。
  • Many engineers shy away from spherical projection methods.许多工程师对球面投影法有畏难情绪。
7 depressed xu8zp9     
adj.沮丧的,抑郁的,不景气的,萧条的
参考例句:
  • When he was depressed,he felt utterly divorced from reality.他心情沮丧时就感到完全脱离了现实。
  • His mother was depressed by the sad news.这个坏消息使他的母亲意志消沉。
8 circumference HOszh     
n.圆周,周长,圆周线
参考例句:
  • It's a mile round the circumference of the field.运动场周长一英里。
  • The diameter and the circumference of a circle correlate.圆的直径与圆周有相互关系。
9 spikes jhXzrc     
n.穗( spike的名词复数 );跑鞋;(防滑)鞋钉;尖状物v.加烈酒于( spike的第三人称单数 );偷偷地给某人的饮料加入(更多)酒精( 或药物);把尖状物钉入;打乱某人的计划
参考例句:
  • a row of iron spikes on a wall 墙头的一排尖铁
  • There is a row of spikes on top of the prison wall to prevent the prisoners escaping. 监狱墙头装有一排尖钉,以防犯人逃跑。 来自《简明英汉词典》
10 latitudes 90df39afd31b3508eb257043703bc0f3     
纬度
参考例句:
  • Latitudes are the lines that go from east to west. 纬线是从东到西的线。
  • It was the brief Indian Summer of the high latitudes. 这是高纬度地方的那种短暂的晚秋。
11 meridian f2xyT     
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。
12 virtue BpqyH     
n.德行,美德;贞操;优点;功效,效力
参考例句:
  • He was considered to be a paragon of virtue.他被认为是品德尽善尽美的典范。
  • You need to decorate your mind with virtue.你应该用德行美化心灵。
13 perpendicularly 914de916890a9aa3714fa26fe542c2df     
adv. 垂直地, 笔直地, 纵向地
参考例句:
  • Fray's forehead was wrinkled both perpendicularly and crosswise. 弗雷的前额上纹路纵横。
  • Automatic resquaring feature insures nozzle is perpendicularly to the part being cut. 自动垂直功能,可以确保刀头回到与工件完全垂直的位置去切割。


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