Book III chapter 17

On the Use and Excellence¹ of Versoria: and how iron versoria used as pointers in sun-dials, and the fine needles of the mariners²' compass, are to be rubbed, that they may acquire stronger verticity.

V ersoria prepared by the loadstone subserve so many actions in human life that it will not be out of place to record a better method of touching³ them and exciting them magnetically, and a suitable manner of operating. Rich ores of iron and such as yield a greater proportion of metal are recognized by means of an iron needle suspended in æquilibrium and magnetically prepared; and magnetick stones, clays, and earths are distinguished⁴, whether crude or prepared. An iron needle (the soul of the mariners' compass), the marvellous director in voyages and finger of God, one might almost say, indicates the course, and has pointed⁵ out the whole way around the earth (unknown for so many ages). The Spaniards (as also the English) have frequently circumnavigated (by an immense circuit) the whole globe by aid of the mariners' compass. Those who travel about through the world or who sit at home have sun-dials. A magnetick pointer follows and searches out the veins⁶ of ore in mines. By its aid mines are driven in taking cities; catapults and engines of war are aimed by night; it has been of service for the topography of places, for marking off the areas and position of buildings, and for excavating⁷ aqueducts for water under ground. On it depend instruments designed to investigate its own dip and variation.

When iron is to be quickened by the stone, let it be clean and bright, disfigured by no rust⁸ or dirt, and of the best steel216. Let the stone itself be wiped dry, and let it not be damp with any moisture, but let it be filed gently with some smooth piece of iron. But the hitting of the stone with a hammer is of no advantage. By these means let their bare surfaces be joined, and let them be rubbed, so that they may come together more firmly; not so that the material substance of the stone being joined to the iron may cleave⁹ to it, but they are rubbed gently together with friction¹⁰, and

(useless parts being rubbed off) they are intimately united; whence a more notable virtue¹¹ arises in the iron that is excited. A is the best way of touching a versorium when the cusp touches the pole and faces it; B is a moderately good way, when, though facing it, it is a little way distant from the pole; also in like manner C is only moderately good on account of the cusp being turned away from the pole; D, which is farther distant, is hardly so good; F, which is prepared crosswise along a parallel, is bad; of no virtue and entirely¹² irresponsive and feeble is the magnetick index L, which is rubbed along the æquator; oblique¹³ and not pointing towards the pole as G, and oblique, not pointing toward but turned away from the pole as H, are bad. These have been placed so that they might indicate the distinct forces of a round stone. But mechanicians very often have a stone tending more to a cone¹⁴ shape, and more powerful on account of that shape since the pole, on which they rub their wires, is at the apex¹⁵ of the projecting part. Sometimes the stone has on the top and above its own pole an artificial acorn¹⁶ or snout made of steel for the sake of its power. Iron needles are rubbed on the top of this; wherefore they turn toward the same pole as if they had been prepared on that part of the stone with the acorn removed. Let the stone be large enough and strong; the needle, even if it be rather long, should be sufficiently¹⁷ thick, not very slender; with a moderate cusp, not too sharp, although the virtue is not in the cusp itself only, but in the whole piece of iron. A strong large stone is not unfit for rubbing all needles on, excepting that sometimes by its strength it occasions some dip and disturbance¹⁸ in the iron in the case of longer needles; so that one which, having been touched before, rested in equilibrium¹⁹ in the plane of the horizon, now when touched and excited dips at one end, as far as the upright pin on which it turns permits it. Wherefore in the case of longer versoria, the end which is going to be the Boreal, before it is rubbed, should be a little lighter²⁰, so that it may remain exactly in æquilibrio after it is touched. But a needle in this way prepared does its work worse the farther it is beyond the æquinoctial circle. Let the prepared needle be placed in its capsule, and let it not be touched by any other magneticks, nor remain in the near vicinity of them, lest by their opposing forces, whether powerful or sluggish²¹, it should become uncertain and dull. If you also rub the other end of the needle on the other pole of the stone, the needle will perform its functions more steadily²², especially if it be rather long. A piece of iron touched by a loadstone retains the magnetick virtue, excited in it even for ages²¹⁷, firm and strong, if it is placed according to nature meridionally and not along a parallel, and is not injured by rust or any external injury from the surrounding medium. Porta wrongly seeks for a proportion between the loadstone and the iron: because, he says, a little piece of iron will not be capable of holding much virtue; for it is consumed by the great force of the loadstone. A piece of iron receives its own virtue fully²³, even if it be only of the weight of one scruple²⁴, whilst the mass of the loadstone is a thousand pounds. It is also useless to make the needle rather flat at the end that is touched, so that it may be better and more perfectly²⁵ magnetick, and that it may best receive and hold certain magnetick particles; since hardly any part will stick on a sharp point; because he thought that it was by the adhesion of parts of the loadstone (as it were, hairs) that the influence is imparted and conserved²⁶, though those particles are merely rubbed off by the rubbing of the iron over the softer stone, and the iron none the less points toward the North and South, if after it is touched it be scoured²⁷ with sand or emery powder, or with any other material, even if by long rubbing of this kind the external parts of it are lessened²⁸ and worn away. When a needle is being rubbed, one should always leave off at the end; otherwise, if it is rubbed on the loadstone from the point toward the middle, less verticity is excited in the iron, sometimes none at all, or very little. For where the last contact is, there is the pole and goal of verticity. In order that a stronger verticity may be produced in the iron by rubbing on the loadstone, one ought in northern lands to turn the true northern pole of the loadstone toward the highest part of the sky; on this pole that end of the needle is going to be rubbed, which shall afterwards turn toward the north of the earth; whilst it will be an advantage for the other end of the needle to be rubbed on the southern pole of the terrella turned toward the earth, and this being so excited will incline toward the south. In southern regions beyond the æquator the plan is just the contrary. The reason of this dissimilarity is demonstrated, Book II., chap, xxxiv., in which it is shown (by a manifest combination of a terrella and the earth) why the poles of a loadstone, for different reasons, are one stronger than the other. If a needle be touched between the mutually accordant poles of two loadstones, equal in power, shape, and mass, no strength is acquired by the needle. A and B are two loadstones attracting one another, according to nature, at their dissimilar ends; C, the point of a needle touched by both at once, is not excited (even if those loadstones be connected according to nature), if they are equal; but if they are not equal, virtue is acquired from the stronger. When a needle is being excited by a loadstone, begin in the middle, and draw the needle toward its end; at the end let the application be continued with a very gentle rubbing around the end for some time; that is to say, for one or two minutes; do not repeat the motion from the middle to the end (as is frequently done) for in this way the verticity is injured. Some delay is desirable, for although the power is imparted instantly, and the iron excited, yet from the vicinity of the loadstone and a suitable delay, a more steady verticity arises, and one that is more firmly durable²⁹ in the iron. Although an armed stone raises a greater weight of iron than an unarmed one, yet a needle is not more strongly excited by an armed stone than by an unarmed one. Let there be two iron wires of the same length, wrought³⁰ from the same wire; let one be excited by an armed end, the other by an unarmed end; it is manifest that the same needles have a beginning of motion or a sensible inclination³¹ at equal distances from the same armed and unarmed loadstone; this is ascertained³² by measuring with a longish reed. But objects which are more powerfully excited move more quickly; those which are less powerfully excited, more feebly, and not unless brought rather close; the experiment is made on water with equal corks³³.

1 excellence   

n.优秀，杰出，(pl.)优点，美德

参考例句：

• His art has reached a high degree of excellence.他的艺术已达到炉火纯青的地步。
• My performance is far below excellence.我的表演离优秀还差得远呢。

2 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。

3 touching   

adj.动人的，使人感伤的

参考例句：

• It was a touching sight.这是一幅动人的景象。
• His letter was touching.他的信很感人。

4 distinguished   

adj.卓越的，杰出的，著名的

参考例句：

• Elephants are distinguished from other animals by their long noses.大象以其长长的鼻子显示出与其他动物的不同。
• A banquet was given in honor of the distinguished guests.宴会是为了向贵宾们致敬而举行的。

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 veins   

n.纹理；矿脉( vein的名词复数 )；静脉；叶脉；纹理

参考例句：

• The blood flows from the capillaries back into the veins. 血从毛细血管流回静脉。 来自《简明英汉词典》
• I felt a pleasant glow in all my veins from the wine. 喝过酒后我浑身的血都热烘烘的，感到很舒服。 来自《简明英汉词典》

7 excavating   

v.挖掘( excavate的现在分词 )；开凿；挖出；发掘

参考例句：

• A bulldozer was employed for excavating the foundations of the building. 推土机用来给楼房挖地基。 来自《简明英汉词典》
• A new Danish expedition is again excavating the site in annual summer digs. 一支新的丹麦探险队又在那个遗址上进行一年一度的夏季挖掘。 来自辞典例句

8 rust   

n.锈；v.生锈；(脑子)衰退

参考例句：

• She scraped the rust off the kitchen knife.她擦掉了菜刀上的锈。
• The rain will rust the iron roof.雨水会使铁皮屋顶生锈。

9 cleave   

v．(clave；cleaved)粘着，粘住；坚持；依恋

参考例句：

• It examines how the decision to quit gold or to cleave to it affected trade policies.论文分析了放弃或坚持金本位是如何影响贸易政策的。
• Those who cleave to the latter view include many conservative American politicians.坚持后一种观点的大多是美国的保守派政客。

10 friction   

n.摩擦，摩擦力

参考例句：

• When Joan returned to work,the friction between them increased.琼回来工作后，他们之间的摩擦加剧了。
• Friction acts on moving bodies and brings them to a stop.摩擦力作用于运动着的物体，并使其停止。

11 virtue   

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。

12 entirely   

ad.全部地，完整地；完全地，彻底地

参考例句：

• The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
• His life was entirely given up to the educational work. 他的一生统统献给了教育工作。

13 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。

14 cone   

n.圆锥体，圆锥形东西，球果

参考例句：

• Saw-dust piled up in a great cone.锯屑堆积如山。
• The police have sectioned off part of the road with traffic cone.警察用锥形路标把部分路面分隔开来。

15 apex   

n.顶点，最高点

参考例句：

• He reached the apex of power in the early 1930s.他在三十年代初达到了权力的顶峰。
• His election to the presidency was the apex of his career.当选总统是他一生事业的顶峰。

16 acorn   

n.橡实，橡子

参考例句：

• The oak is implicit in the acorn.橡树孕育于橡子之中。
• The tree grew from a small acorn.橡树从一粒小橡子生长而来。

17 sufficiently   

adv.足够地，充分地

参考例句：

• It turned out he had not insured the house sufficiently.原来他没有给房屋投足保险。
• The new policy was sufficiently elastic to accommodate both views.新政策充分灵活地适用两种观点。

18 disturbance   

n.动乱，骚动；打扰，干扰；(身心)失调

参考例句：

• He is suffering an emotional disturbance.他的情绪受到了困扰。
• You can work in here without any disturbance.在这儿你可不受任何干扰地工作。

19 equilibrium   

n.平衡，均衡，相称，均势，平静

参考例句：

• Change in the world around us disturbs our inner equilibrium.我们周围世界的变化扰乱了我们内心的平静。
• This is best expressed in the form of an equilibrium constant.这最好用平衡常数的形式来表示。

20 lighter   

n.打火机，点火器；驳船；v.用驳船运送；light的比较级

参考例句：

• The portrait was touched up so as to make it lighter.这张画经过润色，色调明朗了一些。
• The lighter works off the car battery.引燃器利用汽车蓄电池打火。

21 sluggish   

adj.懒惰的，迟钝的，无精打采的

参考例句：

• This humid heat makes you feel rather sluggish.这种湿热的天气使人感到懒洋洋的。
• Circulation is much more sluggish in the feet than in the hands.脚部的循环比手部的循环缓慢得多。

22 steadily   

adv.稳定地；不变地；持续地

参考例句：

• The scope of man's use of natural resources will steadily grow.人类利用自然资源的广度将日益扩大。
• Our educational reform was steadily led onto the correct path.我们的教学改革慢慢上轨道了。

23 fully   

adv.完全地，全部地，彻底地；充分地

参考例句：

• The doctor asked me to breathe in,then to breathe out fully.医生让我先吸气，然后全部呼出。
• They soon became fully integrated into the local community.他们很快就完全融入了当地人的圈子。

24 scruple   

n./v.顾忌，迟疑

参考例句：

• It'seemed to her now that she could marry him without the remnant of a scruple.她觉得现在她可以跟他成婚而不需要有任何顾忌。
• He makes no scruple to tell a lie.他说起谎来无所顾忌。

25 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。

26 conserved   

v.保护，保藏，保存( conserve的过去式和过去分词 )

参考例句：

• He conserved his energy for the game. 他为比赛而养精蓄锐。 来自《简明英汉词典》
• Under these conditions, the total mechanical energy remains constant, or is conserved. 在这种条件下，总机械能保持不变或机械能保存。 来自辞典例句

27 scoured   

走遍（某地）搜寻（人或物）( scour的过去式和过去分词 )； （用力）刷； 擦净； 擦亮

参考例句：

• We scoured the area for somewhere to pitch our tent. 我们四处查看，想找一个搭帐篷的地方。
• The torrents scoured out a channel down the hill side. 急流沿着山腰冲刷出一条水沟。

28 lessened   

减少的，减弱的

参考例句：

• Listening to the speech through an interpreter lessened its impact somewhat. 演讲辞通过翻译的嘴说出来，多少削弱了演讲的力量。
• The flight to suburbia lessened the number of middle-class families living within the city. 随着迁往郊外的风行，住在城内的中产家庭减少了。

29 durable   

adj.持久的，耐久的

参考例句：

• This raincoat is made of very durable material.这件雨衣是用非常耐用的料子做的。
• They frequently require more major durable purchases.他们经常需要购买耐用消费品。

30 wrought   

v.引起；以…原料制作；运转；adj.制造的

参考例句：

• Events in Paris wrought a change in British opinion towards France and Germany.巴黎发生的事件改变了英国对法国和德国的看法。
• It's a walking stick with a gold head wrought in the form of a flower.那是一个金质花形包头的拐杖。

31 inclination   

n.倾斜；点头；弯腰；斜坡；倾度；倾向；爱好

参考例句：

• She greeted us with a slight inclination of the head.她微微点头向我们致意。
• I did not feel the slightest inclination to hurry.我没有丝毫着急的意思。

32 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》

33 corks   

n.脐梅衣；软木( cork的名词复数 )；软木塞

参考例句：

• Champagne corks were popping throughout the celebrations. 庆祝会上开香槟酒瓶塞的砰砰声不绝於耳。 来自辞典例句
• Champagne corks popped, and on lace tablecloths seven-course dinners were laid. 桌上铺着带装饰图案的网织的桌布，上面是七道菜的晚餐。 来自飘（部分）