Book III chapter 9

Figures illustrating¹ direction and showing varieties of rotations².

Versorium on loadstone.

P assing from the probable cause of motion toward fixed³ points (according to magnetick laws and principles), it remains⁴ for us to indicate those motions. Above a round loadstone (whose poles are A, B) let a versatory needle be placed whose cusp has been excited by the pole A; that cusp is certainly directed toward A, and is strongly attracted by A; because, having been touched by A, it is in true harmony with A, and combines with it; and yet it is called contrary, because when the versorium is separated from the stone, it is seen to be moved toward the opposite part of the earth to that toward which the pole A of the loadstone is moved.

For if A be the northern pole of the terrella, the cusp is the southern end of the needle, of which the other end (namely, the cross) is pointed⁵ to B; so B is the southern pole of the loadstone, but the cross is the northern end of the versorium. So also the cusp is attracted by E, F, G, H, and by every part of a meridian⁶, from the æquator toward the pole, by the faculty⁷ disponent; and when the versorium is on the same parts of the meridian, the cusp is directed toward A. For it is not the point A that turns the versorium toward it, but the whole loadstone; as also the whole earth does, in the turning of loadstones to the earth.

Figures illustrating magnetick directions in a right sphere²⁰⁸ of stone, and in the right sphere of the earth, as well as the polar directions to the perpendicular⁸ of the poles. All these cusps have been touched by the pole A; all the cusps are turned toward A, excepting that one which is repelled⁹ by B.

 

oblique¹¹ loadstone." alt="Directions above the body of an oblique loadstone." src="https://ebooks.adelaide.edu.au/g/gilbert/william/on-the-magnet/figures/illo119.jpg" />

Figures illustrating horizontal directions above the body of a loadstone. All the cusps that have been made southern by rubbing on the boreal pole, or some place round the northern pole A, turn toward the pole A, and turn away from the southern pole B, toward which all the crosses look. I call the direction horizontal, because it is arranged along the plane of the horizon; for nautical¹⁰ and horological instruments are so constructed that the iron hangs or is supported in æquilibrium on the point of a sharp pin, which prevents the dipping of the versorium, about which we intend to speak later. And in this way it is of the greatest use to man, indicating and distinguishing all the points of the horizon and the winds. Otherwise on every oblique sphere (whether of stone or the earth) versoria and all magnetick substances would have a dip by their own nature below the horizon; and at the poles the directions would be perpendicular, which appears in our discussion On Declination.

A round stone (or terrella) cut in two at the æquator; and all the cusps have been touched by the pole A. The points at the centre of the earth, and between the two parts of the terrella which has been cut in two through the plane of the æquator, are directed as in the present²⁰⁹ diagram. This would also happen in the same way if the division of the stone were through the plane of a tropick, and the mutual¹² separation of the divided parts and the interval¹³ between them were the same as before, when the loadstone was divided through the plane of the æquator, and the parts separated. For the cusps are repelled by C, are attracted by D; and the versoria are parallel, the poles or the verticity in both ends mutually requiring it.

Half a terrella by itself and its directions, unlike the directions of the two parts close to one another as shown in the figure above. All the cusps have been touched by A; all the crosses below except the middle one tend toward the loadstone, not straight, but obliquely¹⁴; because the pole is in the middle of the plane which before was the plane of the æquator. All cusps touched by places distant from the pole move toward the pole (exactly the same as if they had been rubbed upon the pole itself), not toward the place where they were rubbed, wherever that may have been in the undivided stone in some latitude¹⁵ between the pole and the æquator. And for this reason there are only two distinctions of regions, northern and southern, in the terrella, just as in the general terrestrial globe, and there is no eastern nor western place; nor are there any eastern or western regions, rightly speaking; but they are names used in respect of one another toward the eastern or western part of the sky. Wherefore it does not appear that Ptolemy did rightly in his Quadripartitum, making eastern and western districts and provinces, with which he improperly¹⁶ connects the planets, whom the common crowd of philosophizers and the superstitious¹⁷ soothsayers follow.

1 illustrating   

给…加插图( illustrate的现在分词 )； 说明； 表明； （用示例、图画等）说明

参考例句：

• He upstaged the other speakers by illustrating his talk with slides. 他演讲中配上幻灯片，比其他演讲人更吸引听众。
• Material illustrating detailed structure of graptolites has been etched from limestone by means of hydrofluoric acid. 表明笔石详细构造的物质是利用氢氟酸从石灰岩中侵蚀出来。

2 rotations   

旋转( rotation的名词复数 )； 转动； 轮流； 轮换

参考例句：

• Farmers traditionally used long-term rotations of hay, pasture, and corn. 农民以往长期实行干草、牧草和玉米轮作。
• The crankshaft makes three rotations for each rotation of the rotor. 转子每转一周，曲轴转3周。

3 fixed   

adj.固定的，不变的，准备好的；(计算机)固定的

参考例句：

• Have you two fixed on a date for the wedding yet?你们俩选定婚期了吗？
• Once the aim is fixed,we should not change it arbitrarily.目标一旦确定，我们就不应该随意改变。

4 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

5 pointed   

adj.尖的，直截了当的

参考例句：

• He gave me a very sharp pointed pencil.他给我一支削得非常尖的铅笔。
• She wished to show Mrs.John Dashwood by this pointed invitation to her brother.她想通过对达茨伍德夫人提出直截了当的邀请向她的哥哥表示出来。

6 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。

7 faculty   

n.才能；学院，系；(学院或系的)全体教学人员

参考例句：

• He has a great faculty for learning foreign languages.他有学习外语的天赋。
• He has the faculty of saying the right thing at the right time.他有在恰当的时候说恰当的话的才智。

8 perpendicular   

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。

9 repelled   

v.击退( repel的过去式和过去分词 )；使厌恶；排斥；推开

参考例句：

• They repelled the enemy. 他们击退了敌军。 来自《简明英汉词典》
• The minister tremulously, but decidedly, repelled the old man's arm. 而丁梅斯代尔牧师却哆里哆嗦地断然推开了那老人的胳臂。 来自英汉文学 - 红字

10 nautical   

adj.海上的，航海的，船员的

参考例句：

• A nautical mile is 1,852 meters.一海里等于1852米。
• It is 206 nautical miles from our present location.距离我们现在的位置有206海里。

11 oblique   

adj.斜的，倾斜的，无诚意的，不坦率的

参考例句：

• He made oblique references to her lack of experience.他拐弯抹角地说她缺乏经验。
• She gave an oblique look to one side.她向旁边斜看了一眼。

12 mutual   

adj.相互的，彼此的；共同的，共有的

参考例句：

• We must pull together for mutual interest.我们必须为相互的利益而通力合作。
• Mutual interests tied us together.相互的利害关系把我们联系在一起。

13 interval   

n.间隔，间距；幕间休息，中场休息

参考例句：

• The interval between the two trees measures 40 feet.这两棵树的间隔是40英尺。
• There was a long interval before he anwsered the telephone.隔了好久他才回了电话。

14 obliquely   

adv.斜； 倾斜； 间接； 不光明正大

参考例句：

• From the gateway two paths led obliquely across the court. 从门口那儿，有两条小路斜越过院子。 来自辞典例句
• He was receding obliquely with a curious hurrying gait. 他歪着身子，古怪而急促地迈着步子，往后退去。 来自辞典例句

15 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。

16 improperly   

不正确地，不适当地

参考例句：

• Of course it was acting improperly. 这样做就是不对嘛！
• He is trying to improperly influence a witness. 他在试图误导证人。

17 superstitious   

adj.迷信的

参考例句：

• They aim to deliver the people who are in bondage to superstitious belief.他们的目的在于解脱那些受迷信束缚的人。
• These superstitious practices should be abolished as soon as possible.这些迷信做法应尽早取消。