卷三·第 120–127 问　诸天层层与两种运动

BOOK III. ASTRONOMY

卷三　天文

§120. What is the orb?

第一百二十问　何谓“天”？

It is a spherical body moving in its place, containing within it things that do not by their nature move as it moves; and we are at its centre. It is called falak ('orb') because of its roundness and its motion, likening it to the whorl (falka) of a spindle. Among the philosophers its name is ether.

它是一个在自己的位置上运动的球形物体，里面包含着一些按其本性不随它一同运动的东西；而我们就在它的中心。它被称为“法拉克”（天），是因为它圆而且转动，人们把它比作纺锤上的纺轮（法勒卡）。在哲学家那里，它的名字是以太。

§121. Is it one, or more?

第一百二十一问　天是一个，还是不止一个？

The orbs are 8 spheres enclosed one within another, like the layers of an onion. The smallest of them, nearest to the centre, is the one in which the Moon swims; she alone ascends and descends within its thickness. Each sphere has a certain thickness in depth, so that its planet may have through it two distances, a farthest and a nearest. The second sphere, above it, is Mercury's; the third Venus'; the fourth the Sun's; the fifth Mars'; the sixth Jupiter's; and the seventh Saturn's. These are the spheres of the 7 wandering planets. Above them is the sphere of the stars known as fixed. This is its figure:

诸天是八个球层，一个包在另一个里面，像洋葱的层层。其中最小、离中心最近的，是月亮在其中游动的那一层；只有月亮在这一层的厚度之内升降。每一个球层在深度上都有一定的厚度，使其中的行星在它里面能有两种距离，一个最远，一个最近。在它上面的第二个球层属水星，第三个属金星，第四个属太阳，第五个属火星，第六个属木星，第七个属土星。这些是七颗游星的球层。在它们之上，是那些号称恒星的星的球层。它的图形如下：

§122. What lies beyond the eighth orb?

第一百二十二问　第八重天之外是什么？

Some people hold that beyond it there is a ninth orb at rest, the one the Indians call in their language brahmāṇḍa, that is, the egg of Brahmā; for the first mover must not be in motion, and so they made it at rest. But it must not be a body either, as the demonstrations make plain, so calling it an orb is an error. Some of the ancients place beyond it an infinite void, and some an infinite body. According to Aristotle there is beyond the limit of bodies neither body nor void.

有些人认为它外面还有一个静止的第九重天，就是印度人用他们的语言称为“婆罗摩安荼”、意思是梵天之卵的那个；因为第一推动者不应当处于运动之中，所以他们让它静止。但它也不应当是物体，这一点由证明可以明白，所以称它为天是错误的。古人中有些人在它外面安放了无限的虚空，有些人安放了无限的物体。依亚里士多德之说，在诸物体的界限之外，既没有物体，也没有虚空。

§123. What is the sky?

第一百二十三问　何谓天空？

In the language, 'sky' is whatever is above you and overshadows you, so that the name is applied, with qualification, to the clouds and to the roofs of houses. Without qualification, it is the raised roof of the world, which is the orb mentioned before. For this reason the Persians call it in their language āsmān, that is, 'like a millstone', on account of its circular motion.

在语言里，“天空”是在你上方、覆盖着你的任何东西，所以这个名称加上限定之后，也可以用于云和屋顶。不加限定时，它就是世界高高撑起的屋顶，也就是前面所说的天。因此波斯人在他们的语言里称它为“阿斯曼”，意思是“像磨盘一样”，因为它做圆周运动。

§124. What is within the orb of the Moon?

第一百二十四问　月亮天以内是什么？

The earth is at the centre, and the centre is in truth the bottom. The earth is round as a whole, and jagged in its parts, because of the mountains that project and the hollows that sink. This does not take it out of the spherical form when the senses take it in as a whole, for the sizes of the mountains, however lofty, are small in comparison with the whole earth. Do you not see that if grains like millet project from a sphere a cubit or two in diameter, and as many sink into it, that does not prevent our treating it, approximately, as round? Were it not for this jaggedness, the water would surround it on all sides and cover it, so that nothing of it would appear. For although water shares with earth in heaviness and in falling downward, there is a difference between them in this, by which water is lighter in comparison with earth. For that reason earth settles in water, and the sediment sinks to the bottom, whereas water does not enter the body of the earth itself, but flows into its gaps and mixes with the air there; and when water presses on the air that has entered those gaps, it sinks into them and the air comes out of them, just as rain falls from the clouds through the air. When parts of the earth's surface had risen up, the water drew off into the depths and became seas, and water and earth together became a single sphere, surrounded on all sides by air. Then the part of the air that touches the orb of the Moon is heated through the motion and the friction of the two bodies in contact, and so it is the fire surrounding the air, its thickness diminishing towards the two poles because the motion grows slower near them. This is its figure:

地居中心，而中心其实就是下方。地整体上是圆的，各部分则高低不平，因为有山峰突起、有洼地下陷。但从感官整体来看，这并不使它失去球形，因为群山无论多高，与整个大地相比都很小。你没看见吗？一个直径一两肘尺的球，若有小米那样的颗粒从它上面突起，又有同样多的陷进去，这并不妨碍我们把它大致当作圆的。若不是有这种高低不平，水就会从四面八方把地包围、淹没，使它一点也露不出来。因为水虽然与土同样有重量、同样向下落，但二者在这一点上有所不同：与土相比，水较轻。所以土会沉到水里，渣滓沉到底；而水不会进入土本身之中，只会流进它的缝隙，在那里与空气相混；当水压在进入那些缝隙的空气上时，水就沉入缝隙，空气则从中出来，正如雨从云中穿过空气落下一样。当地面的一些部分隆起之后，水就退到深处，成为海洋，水与土合成一个球，四面都被空气包围。然后，与月亮天相接的那部分空气，因两个相接物体的运动与摩擦而变热，于是成为包围着空气的火；它的厚度向两极逐渐减小，因为在两极附近运动变慢。它的图形如下：

§125. What are the fixed stars and the planets?

第一百二十五问　何谓恒星与行星？

The fixed stars are those spread through the whole sky, their distances fixed for ever, none approaching another or moving away from it. In Persian they are called biyābānī ('of the desert'), because one finds the way in the wastes by them. The planets are the 7, each of which has a sphere of its own. Each of them never ceases approaching the other planets and the fixed stars and moving away from them, in coming into line with them and facing them; that is because of its motion and the speed of its course.

恒星是遍布整个天空的星，它们之间的距离永远固定，没有一颗接近另一颗或离开它。在波斯语里它们被称为“比亚巴尼”，意思是“荒野的”，因为人们在荒野中靠它们找路。行星就是那七颗，每一颗都有自己的一个球层。它们每一颗都不断地接近其他行星和恒星，又离开它们，与它们排成一线、与它们相对；这是由于它的运动和它运行的速度。

§126. What is the first, westward motion?

第一百二十六问　何谓第一运动，即西向运动？

It is the motion by which each of the Sun, the Moon and the stars is seen rising, ascending until it reaches its highest point, then declining from it little by little, then setting, and after that returning to its place of rising. In the luminous bodies this motion is perceptible, and is hidden from no animal as it goes about seeking its livelihood, let alone from man. Some animals move in accordance with it, such as the chameleon, which faces the Sun however it turns; and so do the leaves of plants, most clearly the leaves of the mung bean and the lily. This motion is called the first because it is the first of the heavenly motions to be perceived, and westward because the furthest point that what is moved by it can be seen to reach is its setting.

这就是使太阳、月亮和群星各自被看到升起、上升到最高处、然后从那里一点一点下降、再落下、此后又回到升起之处的那种运动。在发光的天体上，这种运动是感官可以察觉的，任何动物在四处觅食时都不会看不到它，更不必说人了。有些动物顺着它而动，例如变色龙，太阳无论转到哪里，它都面向太阳；植物的叶子也是这样，最明显的是绿豆与百合的叶子。这种运动被称为第一运动，因为它是天上诸运动中最先被察觉的；被称为西向运动，是因为被它带动的东西所能被看到到达的最远之处，就是它的落下。

§127. What is the second, eastward motion?

第一百二十七问　何谓第二运动，即东向运动？

Each of the stars moves towards the quarter from which the rising takes place. In all the fixed stars this motion is small in amount, and it is because the distances between them stay fixed that they were called fixed. In the planets it is greater and more evident, and moreover irregular; and in the Moon, because of her speed, it is much plainer still. For from her first appearance as a crescent in the west she increases her distance each night from the Sun and from the stars that lie between her and the Sun, and draws nearer to the stars that lie between the Sun and her on the other side; and when she meets one of them she hides it on the eastern side and reveals it on the western. This motion, which belongs to all of them, is opposite to the first in direction, but does not face it squarely; it inclines a little. It is called the second because its amount varies in each of the stars, whereas the first is uniform for all; it overpowers them and carries them round while they move contrary to it, as the passengers of a ship move in the direction of the water's flow while they walk within it against the flow; and uniformity has over variation the merit of precedence. Nor is this motion equally evident: to recognise it one needs reasoning drawn from sense perception. It is called eastward because what is moved by it heads towards the quarter from which the rising takes place.

每一颗星都向升起所在的那一方运动。在所有恒星中，这种运动的量都很小；正因为它们之间的距离保持固定，它们才被称为恒星。在行星中，这种运动较大、较明显，而且不均匀；在月亮，由于她走得快，就更加明显得多。因为她从第一次在西方以新月出现起，每一夜都更远离太阳，也更远离位于她与太阳之间的那些星，而更接近从另一侧位于太阳与她之间的那些星；当她遇到其中一颗时，就在东侧把它遮住，在西侧把它显露出来。这种为所有星所共有的运动，在方向上与第一运动相反，但并不正面相对，而是稍稍倾斜。它被称为第二运动，是因为它的量在每颗星上都不同，而第一运动对一切星都是均匀的；第一运动压倒它们，带着它们旋转，而它们则逆着它运动，正如船上的乘客随着水流的方向而行，同时又在船内逆着水流行走；而均匀比起变化，有占先的资格。这种运动也不是同样明显：要认出它，需要从感官知觉中引出推理。它被称为东向运动，是因为被它带动的东西朝着升起所在的那一方前进。