《论衡·卷十一·说日篇》
大约四十一二个月，有一次日食；一百八十天，有一次月蚀。日食月食都有一定时间，违背时间就是变异，至于发生变异，也是气自然而然形成的。
大率四十一二月，日一食，百八十日，月一蚀，蚀之皆有时，非时为变，及其为变，气自然也。
There is a solar eclipse every forty-one or two months; there is a lunar eclipse every 180 days. The solar eclipse and the lunar eclipse have a certain time, and it is a variation if the time is violated. As for the variation, it is formed naturally by the air.