Chap. xii.
A long piece of Iron, even though not excited by a loadstone, settles itself toward North and South.
E very good and perfect piece of iron, if drawn1 out in length, points North and South, just as the loadstone or iron rubbed with a magnetical body does; a thing that our famous philosophers have little understood, who have sweated in vain to set forth2 the magnetick virtues3 and the causes of the friendship of iron for the stone. You may experiment with either large or small iron works, and either in air or in water. A straight piece of iron six feet long of the thickness of your finger is suspended (in the way described in the foregoing chapter) in exact æquipoise by a strong and slender silken cord. But the cord should be cross-woven of several silk filaments4, not twisted simply in one way; and it should be in a small chamber5 with all doors and windows closed, that the wind may not enter, nor the air of the room be in any way disturbed; for which reason it is not expedient6 that the trial should be made on windy days, or while a storm is brewing7. For thus it freely follows its bent8, and slowly moves until at length, as it rests, it points with its ends North and South, just as iron touched with a loadstone does in shadow-clocks, and in compasses, and in the mariners9' compass. You will be able, if curious enough, to balance all at the same time by fine threads a number of small rods, or iron wires, or long pins with which women knit stockings; you will see that all of them at the same time are in accord, unless there be some error in this delicate operation: for unless you prepare everything fitly and skilfully10, the labour will be void. Make trial of this thing in water also, which is done both more certainly and more easily. Let an iron wire two or three digits11 long, more or less, be passed through a round cork12, so that it may just float upon water; and as soon as you have committed it to the waves, it turns upon its own centre, and one end tends to the North, the other to the South; the causes of which you will afterwards find in the laws of the direction. This too you should understand, and hold firmly in memory, that as a strong loadstone, and iron touched with the same, do not invariably point exactly to the true pole but to the point of the variation; so does a weaker loadstone, and so does the iron, which directs itself by its own forces only, not by those impressed by the stone; and so every ore of iron, and all bodies naturally endowed with something of the iron nature, and prepared, turn to the same point of the horizon, according to the place of the variation in that particular region (if there be any variation therein), and there abide13 and rest.
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1
drawn
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v.拖,拉,拔出;adj.憔悴的,紧张的 | |
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2
forth
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adv.向前;向外,往外 | |
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3
virtues
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美德( virtue的名词复数 ); 德行; 优点; 长处 | |
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4
filaments
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n.(电灯泡的)灯丝( filament的名词复数 );丝极;细丝;丝状物 | |
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5
chamber
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n.房间,寝室;会议厅;议院;会所 | |
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6
expedient
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adj.有用的,有利的;n.紧急的办法,权宜之计 | |
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7
brewing
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n. 酿造, 一次酿造的量 动词brew的现在分词形式 | |
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8
bent
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n.爱好,癖好;adj.弯的;决心的,一心的 | |
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9
mariners
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海员,水手(mariner的复数形式) | |
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10
skilfully
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adv. (美skillfully)熟练地 | |
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11
digits
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n.数字( digit的名词复数 );手指,足趾 | |
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12
cork
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n.软木,软木塞 | |
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13
abide
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vi.遵守;坚持;vt.忍受 | |
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