登陆注册
4615700000009

第9章 PTOLEMY.(6)

These movements were wholly incompatible with the supposition that the journeys of Venus were described by a single motion of the kind regarded as perfect. It was obvious that the movement was connected in some strange manner with the revolution of the sun, and here was the ingenious method by which Ptolemy sought to render account of it. Imagine a fixed arm to extend from the earth to the sun, as shown in the accompanying figure (Fig. 1), then this arm will move round uniformly, in consequence of the sun's movement. At a point Pon this arm let a small circle be described. Venus is supposed to revolve uniformly in this small circle, while the circle itself is carried round continuously by the movement of the sun. In this way it was possible to account for the chief peculiarities in the movement of Venus. It will be seen that, in consequence of the revolution around P, the spectator on the earth will sometimes see Venus on one side of the sun, and sometimes on the other side, so that the planet always remains in the sun's vicinity. By properly proportioning the movements, this little contrivance simulated the transitions from the morning star to the evening star. Thus the changes of Venus could be accounted for by a Combination of the "perfect" movement of P in the circle which it described uniformly round the earth, combined with the "perfect" motion of Venus in the circle which it described uniformly around the moving centre.

In a precisely similar manner Ptolemy rendered an explanation of the fitful apparitions of Mercury. Now just on one side of the sun, and now just on the other, this rarely-seen planet moved like Venus on a circle whereof the centre was also carried by the line joining the sun and the earth. The circle, however, in which Mercury actually revolved had to be smaller than that of Venus, in order to account for the fact that Mercury lies always much closer to the sun than the better-known planet.

[FIG. 2. PTOLEMY'S THEORY OF THE MOVEMENT OF MARS.]

The explanation of the movement of an outer planet like Mars could also be deduced from the joint effect of two perfect motions. The changes through which Mars goes are, however, so different from the movements of Venus that quite a different disposition of the circles is necessary. For consider the facts which characterise the movements of an outer planet such as Mars. In the first place, Mars accomplishes an entire circuit of the heaven. In this respect, no doubt, it may be said to resemble the sun or the moon. A little attention will, however, show that there are extraordinary irregularities in the movement of the planet. Generally speaking, it speeds its way from west to east among the stars, but sometimes the attentive observer will note that the speed with which the planet advances is slackening, and then it will seem to become stationary.

Some days later the direction of the planet's movement will be reversed, and it will be found moving from the east towards the west. At first it proceeds slowly and then quickens its pace, until a certain speed is attained, which afterwards declines until a second stationary position is reached. After a due pause the original motion from west to east is resumed, and is continued until a similar cycle of changes again commences. Such movements as these were obviously quite at variance with any perfect movement in a single circle round the earth. Here, again, the geometrical sagacity of Ptolemy provided him with the means of representing the apparent movements of Mars, and, at the same time, restricting the explanation to those perfect movements which he deemed so essential. In Fig. 2we exhibit Ptolemy's theory as to the movement of Mars. We have, as before, the earth at the centre, and the sun describing its circular orbit around that centre. The path of Mars is to be taken as exterior to that of the sun. We are to suppose that at a point marked M there is a fictitious planet, which revolves around the earth uniformly, in a circle called the DEFERENT. This point M, which is thus animated by a perfect movement, is the centre of a circle which is carried onwards with M, and around the circumference of which Mars revolves uniformly. It is easy to show that the combined effect of these two perfect movements is to produce exactly that displacement of Mars in the heavens which observation discloses. In the position represented in the figure, Mars is obviously pursuing a course which will appear to the observer as a movement from west to east. When, however, the planet gets round to such a position as R, it is then moving from east to west in consequence of its revolution in the moving circle, as indicated by the arrowhead. On the other hand, the whole circle is carried forward in the opposite direction. If the latter movement be less rapid than the former, then we shall have the backward movement of Mars on the heavens which it was desired to explain. By a proper adjustment of the relative lengths of these arms the movements of the planet as actually observed could be completely accounted for.

The other outer planets with which Ptolemy was acquainted, namely, Jupiter and Saturn, had movements of the same general character as those of Mars. Ptolemy was equally successful in explaining the movements they performed by the supposition that each planet had perfect rotation in a circle of its own, which circle itself had perfect movement around the earth in the centre.

It is somewhat strange that Ptolemy did not advance one step further, as by so doing he would have given great simplicity to his system. He might, for instance, have represented the movements of Venus equally well by putting the centre of the moving circle at the sun itself, and correspondingly enlarging the circle in which Venus revolved. He might, too, have arranged that the several circles which the outer planets traversed should also have had their centres at the sun. The planetary system would then have consisted of an earth fixed at the centre, of a sun revolving uniformly around it, and of a system of planets each describing its own circle around a moving centre placed in the sun. Perhaps Ptolemy had not thought of this, or perhaps he may have seen arguments against it. This important step was, however, taken by Tycho. He considered that all the planets revolved around the sun in circles, and that the sun itself, bearing all these orbits, described a mighty circle around the earth. This point having been reached, only one more step would have been necessary to reach the glorious truths that revealed the structure of the solar system. That last step was taken by Copernicus.

同类推荐
  • 种福堂公选良方

    种福堂公选良方

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • 曲目新编

    曲目新编

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • 外科浸淫疥癣门

    外科浸淫疥癣门

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • 佛顶尊胜陀罗尼经

    佛顶尊胜陀罗尼经

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
  • The Golden Bough

    The Golden Bough

    本书为公版书,为不受著作权法限制的作家、艺术家及其它人士发布的作品,供广大读者阅读交流。汇聚授权电子版权。
热门推荐
  • 快穿之反派大人我错了

    快穿之反派大人我错了

    第一次写,请见谅。洛思晴作为一个先天性情感缺失的人,好不容易在父母的劝说下相了个亲,找了个“男朋友”,最后还被名义上的“闺蜜”抢走了。好吧,利落的杀了两个渣人后,她就被一团黑绒绒砸死了。。。然后,你要我攻略反派?好吧,来吧反派大宝贝,手铐已就绪,就等你了,等等。。。手铐怎么在我身上?统砸,这个反派有bug!!
  • 萌徒成凰:面瘫师尊很焦躁

    萌徒成凰:面瘫师尊很焦躁

    哥哥和未过门的嫂嫂被师父救了,因为他们有命定的姻缘。可是师父怎么也不肯让她亲。真是讨厌。他说你应该去亲那个人,不要亲我。啊呸,我亲的就是你。
  • 体育传播学概论

    体育传播学概论

    本书主要研究内容:体育传播媒介论、体育传播材料论——体育信息、体育传播论、体育传播者论、体育传播过程论、受众论、体育传播效果论。
  • 盛宠娘子

    盛宠娘子

    她在临死之际,才看清了身边男人和妹妹的真面目,她后悔了。重生后,她发誓要做霸气御姐,既然躲不过,她就准备三十六般兵器,把庶妹姨娘渣男打的落花流水,看见她就绕道走。“喂,师兄,你别绕道啊,我不会打你——”
  • 爹地你老婆丢了

    爹地你老婆丢了

    [宠文,1V1,萌宝,女强,女扮男装]“呀呀……痒痒痒……”女人被挠脚心,哈哈大笑。“回答我,为什么六年后回来了?”男人冷阴阴地问。“因为孩子想你了,我……更想你。”女人挑眉微笑。两小包子一人抱一只男人的大腿。“爹地,收了妈咪吧!妈咪很听话,吃的很少,还买一赠二,很划算哦!”“汪……汪……”………………………………海城首富顾家二少突然对某女人宠爱有加,惹起海城全城人民的议论,殊不知,她的身份诡异莫测,而且身边还有两小包子随时待命!“惹我妈咪,死!”“勾引爹地,死!”从此,谁都知道顾家有个被人宠上天的女人。从此,冷若冰霜的大冰块融化成了一片汪洋大海。
  • 妃成勿扰

    妃成勿扰

    【女强+男强+小调情】独占迈克~~【小鸟不发威,你当我是七星瓢虫啊!】初次见面,她毫不犹豫的踢向他,虽疼痛不已,但是命运却将两人紧紧相连。可是阴差阳错,一纸诏书,踏上龙榻。“你又不是处男,你凭什么碰我!”花泽月的这句话被载入了西玥国的重大历史事件中。她故技重施,惹怒皇威,一气之下打入冷宫。天下人尽知她成了皇帝的新欢,她憔悴不堪,深宫之中,我的青春谁做主?为了他,千辛万苦,逃离苦海,却换来了‘你已成妃,何故扰我?’伤心欲绝,撕肺裂心。一朝跳崖,一场失忆,脱胎换骨。机灵古怪,本领高强。冰龙在手,浴火凤凰。天下人尽知‘花家有一女,此为天上来。不食人间烟火,专爱天下美男。’此女子倾国倾城,此女子谁主沉浮?
  • 独步惊华

    独步惊华

    她,顾若云,青龙国有名的废物,父母双亡,天生懦弱,丢尽了整个将军府的脸面,最终因与人纠纷而被亲身爷爷将毫无过错的她活活打死!再次睁眼,脱去了那一身懦弱,她再非昔日的废物小姐!身怀至宝,契约四大神兽,便是青龙国第一高手都抢着要成为她的跟班……丹药?算什么,她随手可以炼制一把。低阶灵器很强大吗?就连她手下使用的都是高阶灵器。你有高级灵兽?抱歉,她身后的圣兽已成千军万马,力压一切豪雄!只是谁能告诉她,这个强大妖孽的男人是怎么回事!为何却死皮赖脸的纠缠着她,更是誓不罢休!----------推荐新文《鬼帝狂妻:纨绔大小姐》依旧女强,妹子们收藏下,么么哒
  • 傍

    一个青年才俊的“杯具”故事。江少杰生而无父,出身卑微,良好的教育并没有给他提供一个公平的奋斗平台。为了生存,为了给相依为命的母亲治病,这个满怀美好人生理想的乡村教师傍上女富豪,从而傍上永不回头的欲望:极尽所能地弑父淫母,杀害胞弟,还把黑手伸向亲妹妹,绝情抛弃恋人的同时复制了儿子的幼年失怙……诱使江少杰走上不归路的,是难以填满的欲壑!
  • 管理中的心理学诡计

    管理中的心理学诡计

    从心理学的角度来看。那些易激发员工积极心理的管理方法都是最好的奖赏:相反,那些易引起员工反感的管理方法都是最差、最没有头脑的管理行为。管理学大师彼得·德鲁克如是说:管理是一种实践,其本质不在于“知”而在于“行”:其验证不在于“逻辑”而在于“成果”。罗唯一权威就是成就。管理的目的,就是让平凡的人做出不平凡的事。领导和管理是两个截然不同的概念,管理者的工作是计划与预算、组织及配置人员、控制并解决问题,其目的是建立秩序:领导者的工作是确定方向、整合相关者、激励和鼓舞员工,其目的是产生变革。
  • 云梦睡虎地秦简的发现

    云梦睡虎地秦简的发现

    《中国文化知识读本:云梦睡虎地泰简的发现》中优美生动的文字、简明通俗的语言、图文并茂的形式,把中国文化中的物态文化、制度文化、行为文化、精神文化等知识要点全面展示给读者。