Records of ancient central solar eclipses in China and variation of the Earth's rotation

It is simply introduced that the principle and method which the records of the ancient central solar eclipses (total and annular solar eclipses) are u sed in the study of secular variation of the Earth's rotation rate in the p ast about 2000 years and more in this paper. The observations and records o f the ancient central and near central solar eclipses in China are discusse d, A series of Delta T, which is able to express the secular variation of t he Earth's rotation, is obtained from 20 reliable eclipses. The acceleratio n of the Moon in its orbit , -26. 0 " /(100a)(2), is used in this paper. Th e mean of the variation of length of the day (I, o, d,) is about 1. 4 ms/10 0 a for epoch of A. D, 1141 according to the result.