PRECESSION OF THE EQUINOXES.

It was with no little impatience¹ that James had waited for the first appearance of the Southern Cross, the emblem² of Australia. He first noticed it when a long way north of the equator, and each evening afterwards bestowed³ a considerable attention upon it. As he made southing on his voyage the glorious constellation⁴ rose higher and higher in the heavens. Hour after hour would he sit, marking its progress, wondering much to see it more or less upright according to the time of night, and more or less declining from the perpendicular⁵ at the same returning hour of evening upon different days.

James could understand the Cross seeming to perform a circle round the south pole of the heavens, as he had seen the Bear round the north pole, from the rotundity of the earth and its daily motion.

It was quite natural, then, that the lad should be so enthusiastic when he spoke⁶ of the constellation to his father in these terms:

“O that pretty Southern Cross! I like it more and more as I get down to the south. I did feel sad to see the old Bear drop gradually, night after night, till it seemed to sink for ever in the northern Atlantic; but I have a new friend here, that keeps rising higher and higher[Pg 29] each night, as if to welcome us to our southern home. How it would please many boys in Europe to see the Cross!

But it was seen in Europe formerly⁷.

Another puzzle, dear father. Did it run away from the south pole to have a look at the north one?

It was not a run, but a gradual slide out of its place, and as gradual a slide back into it again.

What a queer trick! Is it on its rambles⁸ now, I wonder?

It is always on the move.

Yes; I know it describes a circle in the sky once in twenty-four hours, but that is owing to the world rolling over to get its daily light.

Yet it has another motion; not really its own any more than the other. And this leads it further away from the central point over our south pole, and then brings it to its place again.

Well, I am glad it is here now for me. Will there be time for my London cousins to catch a glance at it when it wanders northward¹⁰ again?

O no, no; it does not move quite so fast as that. But if Abraham had been sojourning in southern Europe, instead of Asia, he could have seen it, though it was then making its way back to the south.

How could the Cross slip away from the other southern stars to go on such migrations¹¹?

Not so. All the stars keep their places relatively[Pg 30] to each other, as you see them do in the nightly progress from east to west. In the daily motion none get before the other, nor did the Cross get before its neighbours.

Well, I am fairly done. That is a riddle¹².

Look at the question, boy. What makes the apparent daily motion of the stars?

The real daily motion of the earth.

And if, then, you observe any other peculiarity¹⁴ of movement among your bright friends up there, to what may you reasonably ascribe it?

I should imagine some peculiar¹³ twist, roll, or slipping of this world of ours.

True. And if there be seen among the polar stars, north as well as south, a slight but regular movement, a sort of a swing round, so that some stars get farther off the spot we call the south pole of the heavens, while others approached it nearer, and yet so swung round that at last all find their old places again, how could you get a motion of the earth to make up for all that?

Ah! I must contrive¹⁵ that the world should do three things. It must roll over once a day, roll round the sun once a year, and yet wriggle¹⁶ about in another way at the same time.—Stop a bit—I have it. My top turns round itself, and pretty quickly, too; it shifts about on the floor almost in a circle as it turns round; and I see it, especially when it is quietly spinning, have a slow roll of the head, like a sailor when walking ashore¹⁷, as if its head were a little giddy.

You have hit it exactly, my good fellow. The three motions of your top are much like[Pg 31] the three motions of the world. That top-heavy slow swinging of your top while it is spinning in full force is like a sort of head-rolling of the earth. The poles seem to have a roll of their own, independent of the regular roll.

Yes; and that would make the Polar stars seem as though they were swinging. But how long are they before they are in their regular places again?

Astronomers¹⁸ calculate 25,850 years.

But will not this changing make the star-charts of the ancients all wrong?

Indeed it does. Aries the Ram⁹, for instance, as a sign, is the first thirty degrees on the celestial¹⁹ globe; but as a constellation it has shifted to between the thirtieth and sixtieth degree on the ecliptic. This is called the precession of the Equinoxes.

How is that? I know when the equinoxes are—March 21st and September 23rd—when it is equal night all over the world.

The European vernal equinox took place at the first point of Aries. But by this precession, or more properly recession, or going backward of the stars, the Equinox takes place when the sun is in Taurus the Bull, two thousand years after it was in the Ram.

I see. The stars not only get earlier four minutes a-day to accommodate the earth in its annual motion, but make a change to accommodate the swinging of its pole.

Can you tell me, James, how much the stars slip back in a year?

[Pg 32]Let me calculate it. There are 360 degrees in a circle, and sixty times as many minutes; that is, 21,600. As it is 25,000 years in the circle, the stars would not shift one minute of distance, and the sun’s apparent size in the heavens is thirty minutes, or half-a-degree.

By this Precession a star comes to the same spot about twenty minutes later every year. It is, as it were, sliding back. In Europe, James, one effect has been to bring what we call the Polar star within one degree of the north pole of the heavens; whereas, a few thousand years ago it was twelve degrees off it. The bright star of the Lyre Constellation will some day be the North Polar star.

Ah, but in 25,000 years the present Polar star will be in its old place. The end of the little Bear’s tail seems now fastened on the north pole; but it must be a sort of greasy²⁰ pole for the stars to slip off it as soon as they get near it.”

1 impatience   

n.不耐烦，急躁

参考例句：

• He expressed impatience at the slow rate of progress.进展缓慢，他显得不耐烦。
• He gave a stamp of impatience.他不耐烦地跺脚。

2 emblem   

n.象征，标志；徽章

参考例句：

• Her shirt has the company emblem on it.她的衬衫印有公司的标记。
• The eagle was an emblem of strength and courage.鹰是力量和勇气的象征。

3 bestowed   

赠给，授予( bestow的过去式和过去分词 )

参考例句：

• It was a title bestowed upon him by the king. 那是国王赐给他的头衔。
• He considered himself unworthy of the honour they had bestowed on him. 他认为自己不配得到大家赋予他的荣誉。

4 constellation   

n.星座n.灿烂的一群

参考例句：

• A constellation is a pattern of stars as seen from the earth. 一个星座只是从地球上看到的某些恒星的一种样子。
• The Big Dipper is not by itself a constellation. 北斗七星本身不是一个星座。

5 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。

6 spoke   

n.（车轮的）辐条；轮辐；破坏某人的计划；阻挠某人的行动 v.讲，谈（speak的过去式）；说；演说；从某种观点来说

参考例句：

• They sourced the spoke nuts from our company.他们的轮辐螺帽是从我们公司获得的。
• The spokes of a wheel are the bars that connect the outer ring to the centre.辐条是轮子上连接外圈与中心的条棒。

7 formerly   

adv.从前，以前

参考例句：

• We now enjoy these comforts of which formerly we had only heard.我们现在享受到了过去只是听说过的那些舒适条件。
• This boat was formerly used on the rivers of China.这船从前航行在中国内河里。

8 rambles   

（无目的地）漫游( ramble的第三人称单数 )； （喻）漫谈； 扯淡； 长篇大论

参考例句：

• He rambles in his talk. 他谈话时漫无中心。
• You will have such nice rambles on the moors. 你可以在旷野里好好地溜达溜达。

9 ram   

(random access memory)随机存取存储器

参考例句：

• 512k RAM is recommended and 640k RAM is preferred.推荐配置为512K内存，640K内存则更佳。

10 northward   

adv.向北；n.北方的地区

参考例句：

• He pointed his boat northward.他将船驶向北方。
• I would have a chance to head northward quickly.我就很快有机会去北方了。

11 migrations   

n.迁移，移居( migration的名词复数 )

参考例句：

• It foundered during the turmoils accompanying the Great Migrations. 它在随着民族大迁徙而出现的混乱中崩溃。 来自辞典例句
• Birds also have built-in timepieces which send them off on fall and spring migrations. 鸟类也有天生的时间感应器指导它们秋春迁移。 来自互联网

12 riddle   

n.谜，谜语，粗筛；vt.解谜，给…出谜，筛，检查，鉴定，非难，充满于；vi.出谜

参考例句：

• The riddle couldn't be solved by the child.这个谜语孩子猜不出来。
• Her disappearance is a complete riddle.她的失踪完全是一个谜。

13 peculiar   

adj.古怪的，异常的；特殊的，特有的

参考例句：

• He walks in a peculiar fashion.他走路的样子很奇特。
• He looked at me with a very peculiar expression.他用一种很奇怪的表情看着我。

14 peculiarity   

n.独特性，特色；特殊的东西；怪癖

参考例句：

• Each country has its own peculiarity.每个国家都有自己的独特之处。
• The peculiarity of this shop is its day and nigth service.这家商店的特点是昼夜服务。

15 contrive   

vt.谋划，策划；设法做到；设计，想出

参考例句：

• Can you contrive to be here a little earlier?你能不能早一点来？
• How could you contrive to make such a mess of things?你怎么把事情弄得一团糟呢？

16 wriggle   

v./n.蠕动，扭动；蜿蜒

参考例句：

• I've got an appointment I can't wriggle out of.我有个推脱不掉的约会。
• Children wriggle themselves when they are bored.小孩子感到厌烦时就会扭动他们的身体。

17 ashore   

adv.在(向)岸上，上岸

参考例句：

• The children got ashore before the tide came in.涨潮前，孩子们就上岸了。
• He laid hold of the rope and pulled the boat ashore.他抓住绳子拉船靠岸。

18 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》

19 celestial   

adj.天体的；天上的

参考例句：

• The rosy light yet beamed like a celestial dawn.玫瑰色的红光依然象天上的朝霞一样绚丽。
• Gravity governs the motions of celestial bodies.万有引力控制着天体的运动。

20 greasy   

adj. 多脂的，油脂的

参考例句：

• He bought a heavy-duty cleanser to clean his greasy oven.昨天他买了强力清洁剂来清洗油污的炉子。
• You loathe the smell of greasy food when you are seasick.当你晕船时，你会厌恶油腻的气味。