梅文鼎的日月五星左旋说及其弊端

在中国古代日月五星左、右旋之争中，左旋说到了明清之际已几成沉寂之势。清初，受到传入的西方天文学特别是其多重天说的影响，梅文鼎又提出了一种新的左旋说。梅文鼎的左旋说，是建立在“天”有重数且是一个整体等说法基础上的——故承载日月五星甚至恒星的“各重之天”不得不在外层“动天”的掣动下一起左旋；同时，梅文鼎还有一个重要的辅助创见，即认为起制动作用的“宗动天”的枢纽是北极，而日月五星甚至恒星所在的“各重之天”的枢纽是黄极。这样，就解释了日月五星等在东西向的视运动之外还存在着南北向的视运动以及它们视运动迟疾的差异问题。此外，梅文鼎的模式尽管较诸传统的左旋说更具自洽性，在力学机制上也有所长，但与右旋说尤其是黄百家的右旋说相比，则具有更多的缺陷——主要是论理、实测和应用方面。最后，还探讨了梅文鼎左旋说的思想根源及其影响。

Mei Wending'' s Theory About Left-handed Rotation of the Sun, Moon and Five Planets Around the Earth and Its Drawbacks

In the debate about the left-handed or right-handed rotation of the Sun, Moon and Five Planets (namely, Mercury, Venus, Mars, Jupiter and Saturn) around the Earth, the left-handed rotation theory was almost in silence during the period from Ming Dynasty to Qing Dynasty. In early Qing Dynasty, however, influenced by Western astronomy especially its multi-heaven theory, Mei Wending proposed a new kind of left-handed rotation theory, that is, since the heaven is composed of many layers or circles and as a whole body, every layer of heaven which loads the Sun, Moon, Five Planets or even fixed stars has to rotate leftward dragged by outer layer of motive heaven. Meanwhile according to Mei's viewpoint, the rotation axis of motive heaven is the north pole of heaven, whereas the one of other layers of heaven the ecliptic pole, thus the questions are illuminated, such as the motions in view of the Sun, Moon and Five Planets from north to south as well as from east to west, and in view of their differences of velocity . Furthermore, this paper compares Mei's theory with the right-rotation theories especially the right-rotation theory of his contemporary Huang Baijia, and concludes that Mei's theory has more drawbacks, mainly in reasoning, actual measures and application. In the end, the paper analyses the origin and influence of Mei's theory.