Book vI chapter 6

On the cause of the definite time, of an entire rotation¹ of the Earth.

D iurnal motion is due to causes which have now to be sought, arising from magnetick vigour² and from the confederated bodies; that is to say, why the diurnal³ rotation of the Earth is completed in the space of twenty-four hours. For no curious art, whether of Clepsydras or of sand-clocks, or those contrivances of little toothed wheels which are set in motion by weights, or by the force of a bent⁴ steel band, can discover any degree of difference in the time. But as soon as the diurnal rotation has been gone through, it at once begins over again. But we would take as the day the absolute turning of a meridian⁵ of the Earth, from sun to sun. This is somewhat greater than one whole revolution of it; in this way the yearly course is completed in 365 and nearly ¼ turnings with respect to the sun. From this sure and regular motion of the Earth, the number and time of 365 days, 5 hours, 55 minutes, in solar tropical years is always certain and definite, except that there are some slight differences due to other causes. The Earth therefore revolves⁶ not fortuitously, or by chance, or precipitately⁷; but with a rather high intelligence, equably, and with a wondrous⁸ regularity⁹, in no other way than all the rest of the movable stars, which have definite periods belonging to their motions. For the Sun himself being the agent and incitor of the universe in motion, other wandering globes set within the range of his forces, when acted on and stirred, also regulate each its own proper courses by its own forces; and they are turned about in periods corresponding to the extent of their greater rotation, and the differences of their effused forces, and their intelligence for higher good. And for that cause Saturn¹⁰, having a wider orbit, is borne round it in a longer time, Jupiter a shorter, and Mars still less; while Venus takes nine months, Mercury 80 days, on the hypotheses of Copernicus; the Moon going round the Earth with respect to the Sun in 29 days, 12 hours, 44 minutes. We have asserted that the Earth moves circularly about its centre, completing a day by an entire revolution with respect to the Sun. The Moon revolves in a monthly course around the Earth, and, repeating a conjunction with the Sun after a former synodic conjunction, constitutes the month or Lunar day. The Moon's mean concentrick orbit, according to numerous observations of Copernicus and later astronomers¹¹, is found to be distant 29 and about 5/6 diameters of the Earth from the Earth's centre. The Moon's revolution with respect to the Sun takes place in 29½ days and 44 minutes of time. We reckon the motion with respect to the sun, not the periodic motion, just as a day is one entire revolution of the Earth with respect to the Sun, not one periodick revolution; because the Sun is the cause of lunar as of terrestrial motion: also, because (on the hypotheses of later observers) the synodical month is truly periodic, on account of the Earth's motion in a great orbit. The proportion of diameters to circumferences¹² is the same. And the concentrick orbit of the Moon contains twice over 29 and ½ great circles of the Earth & a little more. The Moon & the Earth, then, agree together in a double proportion of motion; & the Earth moves in the space of twenty-four hours, in its diurnal motion; because the Moon has a motion proportional to the Earth, but the Earth a motion agreeing with the lunar motion in a nearly double proportion. There is some difference in details, because the distances of the stars in details have not been examined sufficiently¹³ exactly, nor are mathematicians¹⁴ as yet agreed about them. The Earth therefore revolves in a space of 24 hours, as the Moon in her monthly course, by a magnetick confederation of both stars, the globes being forwarded in their movement by the Sun, according to the proportion of their orbits, as Aristotle allows, de Cœlo, bk. ii., chap. 10. "It happens" (he says) "that the motions are performed through a proportion existing between them severally, namely, at the same intervals¹⁵ in which some are swifter, others slower," But it is more agreeable to the relation between the Moon and the Earth, that that harmony of motion should be due to the fact that they are bodies rather near together, and very like each other in nature and substance, and that the Moon has more evident effects upon the Earth than the rest of the stars, the Sun excepted; also because the Moon alone of all the planets conducts her revolutions, directly (however diverse even), with reference to the Earth's centre, and is especially akin¹⁶ to the Earth, and bound to it as with chains. This, then, is the true symmetry and harmony between the motions of the Earth and the Moon; not that old oft-besung harmony of cœlestial motions, which assumes that the nearer any sphære is to the Primum Mobile and that fictitious¹⁷ and pretended rapidest Prime Motion, the less does it offer resistance thereto, and the slower it is borne by its own motion from west to east: but that the more remote it is, the greater is its velocity¹⁸, and the more freely does it complete its own movement; and therefore that the Moon (being at the greatest distance from the Primum Mobile) revolves the most swiftly. Those vain tales have been conceded in order that the Primum Mobile may be accepted, and be thought to have certain effects in retarding¹⁹ the motions of the lower heavens; as though the motion of the stars arose from retardation²⁰, and were not inherent and natural; and as though a furious force were perpetually driving the rest of the heaven (except only the Primum Mobile) with frenzied²¹ incitations. Much more likely is it that the stars are borne around symmetrically by their own forces, with a certain mutual²² concert and harmony.

1 rotation   

n.旋转；循环，轮流

参考例句：

• Crop rotation helps prevent soil erosion.农作物轮作有助于防止水土流失。
• The workers in this workshop do day and night shifts in weekly rotation.这个车间的工人上白班和上夜班每周轮换一次。

2 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。

3 diurnal   

adj.白天的，每日的

参考例句：

• Kangaroos are diurnal animals.袋鼠是日间活动的动物。
• Over water the diurnal change in refraction is likely to be small. 在水面上，折光的周日变化可能是很小的。

4 bent   

n.爱好，癖好；adj.弯的；决心的，一心的

参考例句：

• He was fully bent upon the project.他一心扑在这项计划上。
• We bent over backward to help them.我们尽了最大努力帮助他们。

5 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。

6 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》

7 precipitately   

adv.猛进地

参考例句：

• The number of civil wars continued to rise until about 1990 and then fell precipitately. 而国内战争的数量在1990年以前都有增加，1990年后则锐减。 来自互联网
• His wife and mistress, until an hour ago and inviolate were slipping precipitately from his control. 他的妻子和情妇，直到一小时前还是安安稳稳、不可侵犯的，现在却猛不防正从他的控制下溜走。 来自互联网

8 wondrous   

adj.令人惊奇的，奇妙的；adv.惊人地；异乎寻常地；令人惊叹地

参考例句：

• The internal structure of the Department is wondrous to behold.看一下国务院的内部结构是很有意思的。
• We were driven across this wondrous vast land of lakes and forests.我们乘车穿越这片有着湖泊及森林的广袤而神奇的土地。

9 regularity   

n.规律性，规则性；匀称，整齐

参考例句：

• The idea is to maintain the regularity of the heartbeat.问题就是要维持心跳的规律性。
• He exercised with a regularity that amazed us.他锻炼的规律程度令我们非常惊讶。

10 Saturn   

n.农神，土星

参考例句：

• 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。
• These comparisons suggested that Saturn is made of lighter materials.这些比较告诉我们，土星由较轻的物质构成。

11 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》

12 circumferences   

周围，圆周( circumference的名词复数 )

参考例句：

13 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。

14 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

15 intervals   

n.[军事]间隔( interval的名词复数 )；间隔时间；[数学]区间；（戏剧、电影或音乐会的）幕间休息

参考例句：

• The forecast said there would be sunny intervals and showers. 预报间晴，有阵雨。
• Meetings take place at fortnightly intervals. 每两周开一次会。

16 akin   

adj.同族的，类似的

参考例句：

• She painted flowers and birds pictures akin to those of earlier feminine painters.她画一些同早期女画家类似的花鸟画。
• Listening to his life story is akin to reading a good adventure novel.听他的人生故事犹如阅读一本精彩的冒险小说。

17 fictitious   

adj.虚构的，假设的；空头的

参考例句：

• She invented a fictitious boyfriend to put him off.她虚构出一个男朋友来拒绝他。
• The story my mother told me when I was young is fictitious.小时候妈妈对我讲的那个故事是虚构的。

18 velocity   

n.速度，速率

参考例句：

• Einstein's theory links energy with mass and velocity of light.爱因斯坦的理论把能量同质量和光速联系起来。
• The velocity of light is about 300000 kilometres per second.光速约为每秒300000公里。

19 retarding   

使减速( retard的现在分词 )； 妨碍； 阻止； 推迟

参考例句：

• There may be a need for retarding growth chemically to keep trees within bounds. 可能需要用化学剂抑制生长，使树冠保持在一定的范围内。
• In some instances, an aversion to debt is retarding growth. 在某些情况下，对债务的反感正阻碍经济增长。

20 retardation   

n.智力迟钝，精神发育迟缓

参考例句：

• Asbestos reinforcement confers excellent flame retardation properties on a composite. 石棉增强材料使复合材料具有优异的防火性能。
• The theory confirms the increase in the retardation effect with decrease in particle size. 理论证实，随着颗粒尺寸的减小，这一减速效应将增大。

21 frenzied   

a.激怒的；疯狂的

参考例句：

• Will this push him too far and lead to a frenzied attack? 这会不会逼他太甚，导致他进行疯狂的进攻？
• Two teenagers carried out a frenzied attack on a local shopkeeper. 两名十几岁的少年对当地的一个店主进行了疯狂的袭击。

22 mutual   

adj.相互的，彼此的；共同的，共有的

参考例句：

• We must pull together for mutual interest.我们必须为相互的利益而通力合作。
• Mutual interests tied us together.相互的利害关系把我们联系在一起。