Book vI chapter 8

On the Præcession of the Æquinoxes, from the magnetick motion of the poles of the Earth, in the Arctick and Antarctick circle of the Zodiack.

P rimitive mathematicians¹, since they did not pay attention to the inequælities of the years, made no distinction between the æquinoctial, or solstitial revolving² year, and that which is taken from some one of the fixed³ stars. Even the Olympick years, which they used to reckon from the rising of the dogstar, they thought to be the same as those counted from the solstice. Hipparchus of Rhodes was the first to call attention to the fact that these differ from each other, and discovered that the year was longer when measured by the fixed stars than by the æquinox or solstice: whence he supposed that there was in the fixed stars also some motion in a common sequence; but very slow, and not at once perceptible. After him Menelaus, a Roman geometer, then Ptolemy, and long afterward⁴ Mahometes Aractensis, and several more, in all their literary memoirs⁵, perceived that the fixed stars and the whole firmament⁶ proceeded in an orderly sequence, regarding as they did the heaven, not the earth, and not understanding the magnetical inclinations⁷. But we shall demomstrate that it proceeds rather from a certain rotatory motion of the Earth's axis⁹, than that that eighth sphære (so called) the firmament, or non-moving empyrean, revolves¹¹ studded with innumerable globes and stars, whose distances from the Earth have never been proved by anyone, nor can be proved (the whole universe gliding¹², as it were). And surely it should seem much more likely that the appearances in the heavens should be clearly accounted for by a certain inflection and inclination⁸ of the comparatively small body of the Earth, than by the setting in motion of the whole system of the universe; especially if this motion is to be regarded as ordained¹³ solely¹⁴ for the Earth's advantage: While for the fixed stars, or for the planets, it is of no use at all. For this motion the rising and settings of stars in every Horizon, as well as their culminations¹⁵ at the height of the heavens, are shifted so much that the stars which once were vertical¹⁶ are now some degrees distant from the zenith. For nature has taken care, through the Earth's soul or magnetick vigour¹⁷, that, just as it was needful in tempering, receiving, and warding¹⁸ off the sun's rays and light, by suitable seasons, that the points toward which the Earth's pole is directed should be 23 degrees and more from the poles of the Ecliptick250: so now for moderating and for receiving the luminous¹⁹ rays of the fixed stars in due turn and succession, the Earth's poles should revolve¹⁰ at the same distance from the Ecliptick at the Ecliptick's arctick circle; or rather that they should creep at a gentle pace, that the actions of the stars should not always remain at the same parallel circles, but should have a rather slow mutation²⁰. For the influences of the stars are not so forceful as that a swifter course should be desired. Slowly, then, is the Earth's axis inflected; and the stars' rays, falling upon the face of the Earth, shift only in so long a time as a diameter of the arctick or polar circle is extended: whence the star at the extremity²¹ of the tail of the Cynosure²², which once was 12 degrees 24 minutes (namely, in the time of Hipparchus) distant from the pole of the universe, or from that point which the pole of the Earth used to face, is now only 2 degrees and 52 minutes distant from the same point; whence from its nearness it is called by the moderns Polaris. Some time it will be only ½ degree away from the pole: afterward it will begin to recede²³ from the pole until it will be 48 degrees distant; and this, according to the Prutenical tables, will be in Anno Domini 15000. Thus Lucida Lyræ (which to us southern Britons now almost culminates) will some time approach to the pole of the world, to about the fifth degree. So all the stars shift their rays of light at the surface of the Earth, through this wonderful magnetical inflection of the Earth's axis. Hence come new varieties of the seasons of the year, and lands become more fruitful or more barren; hence the characters and manners of nations are changed; kingdoms and laws are altered, in accordance with the virtue²⁵ of the fixed stars as they culminate²⁴, and the strength thence received or lost in accordance with the singular and specifick nature of each; or on account of new configurations²⁶ with the planets in other places of the Zodiack; on account also of risings and settings, and of new concurrences²⁷ at the meridian²⁸. The Præcession of the æquinoxes arising from the aequable motion of the Earth's pole in the arctick circle of the Zodiack is here demonstrated. Let A B C D be the Ecliptick line; I E G the arctic circle of the Zodiack. Then if the Earth's pole look to E, the æquinoxes are at D, C. Let this be at the time of Metho, when the horns of Aries were in the æquinoctial colure. Now if the Earth's pole have advanced to I; then the æquinoxes will be at K, L; and the stars in the ecliptick C will seem to have progressed, in the order of the signs, along the whole arc K C: L will be moved on by the præcession, against the order of the signs, along the arc D L. But this would occur in the contrary order, if the point G were to face the poles of the earth, and the motion were from E to G: for then the æquinoxes would be M N, and the fixed stars would anticipate the same at
C and D, counter to the order of the signs.

1 mathematicians   

数学家( mathematician的名词复数 )

参考例句：

• Do you suppose our mathematicians are unequal to that? 你以为我们的数学家做不到这一点吗？ 来自英汉文学
• Mathematicians can solve problems with two variables. 数学家们可以用两个变数来解决问题。 来自哲学部分

2 revolving   

adj.旋转的，轮转式的；循环的v.（使）旋转( revolve的现在分词 )；细想

参考例句：

• The theatre has a revolving stage. 剧院有一个旋转舞台。
• The company became a revolving-door workplace. 这家公司成了工作的中转站。

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 afterward   

adv.后来；以后

参考例句：

• Let's go to the theatre first and eat afterward. 让我们先去看戏，然后吃饭。
• Afterward,the boy became a very famous artist.后来，这男孩成为一个很有名的艺术家。

5 memoirs   

n.回忆录；回忆录传( mem,自oir的名词复数)

参考例句：

• Her memoirs were ghostwritten. 她的回忆录是由别人代写的。
• I watched a trailer for the screenplay of his memoirs. 我看过以他的回忆录改编成电影的预告片。 来自《简明英汉词典》

6 firmament   

n.苍穹；最高层

参考例句：

• There are no stars in the firmament.天空没有一颗星星。
• He was rich,and a rising star in the political firmament.他十分富有，并且是政治高层一颗冉冉升起的新星。

7 inclinations   

倾向( inclination的名词复数 )； 倾斜； 爱好； 斜坡

参考例句：

• She has artistic inclinations. 她有艺术爱好。
• I've no inclinations towards life as a doctor. 我的志趣不是行医。

8 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。

9 axis   

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。

10 revolve   

vi.(使)旋转；循环出现

参考例句：

• The planets revolve around the sun.行星绕着太阳运转。
• The wheels began to revolve slowly.车轮开始慢慢转动。

11 revolves   

v.（使）旋转( revolve的第三人称单数 )；细想

参考例句：

• The earth revolves both round the sun and on its own axis. 地球既公转又自转。 来自《现代汉英综合大词典》
• Thus a wheel revolves on its axle. 于是，轮子在轴上旋转。 来自《简明英汉词典》

12 gliding   

v. 滑翔 adj. 滑动的

参考例句：

• Swans went gliding past. 天鹅滑行而过。
• The weather forecast has put a question mark against the chance of doing any gliding tomorrow. 天气预报对明天是否能举行滑翔表示怀疑。

13 ordained   

v.任命（某人）为牧师( ordain的过去式和过去分词 )；授予（某人）圣职；（上帝、法律等）命令；判定

参考例句：

• He was ordained in 1984. 他在一九八四年被任命为牧师。 来自《简明英汉词典》
• He was ordained priest. 他被任命为牧师。 来自辞典例句

14 solely   

adv.仅仅，唯一地

参考例句：

• Success should not be measured solely by educational achievement.成功与否不应只用学业成绩来衡量。
• The town depends almost solely on the tourist trade.这座城市几乎完全靠旅游业维持。

15 culminations   

n.顶点，极点（culmination的复数形式）

参考例句：

• For some stars both culminations take place above the horizon. 有些星星两个中天都出现在地平之上。 来自辞典例句

16 vertical   

adj.垂直的，顶点的，纵向的；n.垂直物，垂直的位置

参考例句：

• The northern side of the mountain is almost vertical.这座山的北坡几乎是垂直的。
• Vertical air motions are not measured by this system.垂直气流的运动不用这种系统来测量。

17 vigour   

（=vigor）n.智力，体力，精力

参考例句：

• She is full of vigour and enthusiasm.她有热情，有朝气。
• At 40,he was in his prime and full of vigour.他40岁时正年富力强。

18 warding   

监护，守护（ward的现在分词形式）

参考例句：

• Magina channels a powerful warding magic damping the negative effects of spells. 敌法师用守护魔法来抵御负面法术的攻击。
• Indeed, warding off disruption is the principal property of complex systems. 的确，避免破损解体是复杂系统主要的属性。

19 luminous   

adj.发光的，发亮的；光明的；明白易懂的；有启发的

参考例句：

• There are luminous knobs on all the doors in my house.我家所有门上都安有夜光把手。
• Most clocks and watches in this shop are in luminous paint.这家商店出售的大多数钟表都涂了发光漆。

20 mutation   

n.变化，变异，转变

参考例句：

• People who have this mutation need less sleep than others.有这种突变的人需要的睡眠比其他人少。
• So far the discussion has centered entirely around mutation in the strict sense.到目前为止，严格来讲，讨论完全集中于围绕突变问题上。

21 extremity   

n.末端，尽头；尽力；终极；极度

参考例句：

• I hope you will help them in their extremity.我希望你能帮助在穷途末路的他们。
• What shall we do in this extremity?在这种极其困难的情况下我们该怎么办呢？

22 cynosure   

n.焦点

参考例句：

• Let faith be your cynosure to walk by.让信仰成为你生活中的灯塔。
• The princess,dressed head to foot in gold,was the cynosure of all eyes.公主全身上下披金戴银，是众目注视的焦点。

23 recede   

vi.退(去)，渐渐远去；向后倾斜，缩进

参考例句：

• The colleges would recede in importance.大学的重要性会降低。
• He saw that the dirty water had begun to recede.他发现那污浊的水开始往下退了。

24 culminate   

v.到绝顶，达于极点，达到高潮

参考例句：

• The celebration of the centenary will culminate with a dinner.百年庆典活动将以宴会作为高潮。
• Everyone feared that the boundary dispute between these two countries would culminate in a war.人人都担心,这两国间的边境争端将以一场战争到达顶点。

25 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。

26 configurations   

n.[化学]结构( configuration的名词复数 )；构造；（计算机的）配置；构形（原子在分子中的相对空间位置）

参考例句：

• Such configurations, obtained theoretically by calculation, are called models of a star. 通过理论计算得到的恒星结构称为恒星模型。 来自辞典例句
• The other two configurations have overriding advantages for special applications. 其它两种接法对特殊应用具有突出的优点。 来自辞典例句

27 concurrences   

n.同意，一致( concurrence的名词复数 )；同时发生或出现

参考例句：

28 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。