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.
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.
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.
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.
1 perpendicular | |
adj.垂直的,直立的;n.垂直线,垂直的位置 | |
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2 demonstrations | |
证明( demonstration的名词复数 ); 表明; 表达; 游行示威 | |
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3 rotation | |
n.旋转;循环,轮流 | |
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4 latitude | |
n.纬度,行动或言论的自由(范围),(pl.)地区 | |
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5 axis | |
n.轴,轴线,中心线;坐标轴,基准线 | |
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6 spherical | |
adj.球形的;球面的 | |
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7 depressed | |
adj.沮丧的,抑郁的,不景气的,萧条的 | |
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8 circumference | |
n.圆周,周长,圆周线 | |
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9 spikes | |
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 | |
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10 latitudes | |
纬度 | |
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11 meridian | |
adj.子午线的;全盛期的 | |
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12 virtue | |
n.德行,美德;贞操;优点;功效,效力 | |
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13 perpendicularly | |
adv. 垂直地, 笔直地, 纵向地 | |
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