《易纬·通卦验》中的晷影数据

根据卦气与晷影相应验的宗旨,《易纬·通卦验》记载了一套作为应验标准的晷影数据,与两汉时期其它的晷影数据都不相符合。经检验《易纬》与《周髀算经》、《太初历》等同样采用等差数列法构建晷长数据。《易纬》数据出现在“太初历”之后,后汉《四分历》之前,可能是中国天文学史上等差数列晷影数据的最后一个版本,反映了当时一定的科学认知水平。

Data of shadow cast by the sun on the dial in Yi Wei Tong Gua Yan

According to the correspondence between the length of the shadow cast by the sun on the dial and the Gua-qi theory which correlates the trigrams and hexagrams to the seasonal points, Yi Wei Tong Gua Yan (The Apocrypha of Change: The Comprehensive Examination of the Hexagrams) recorded a set of standard responsive data, which is not in line with the data of other systems of the Han dynasty. By checking these data, we can see that the data in Yi Wei were taken by the same approach of arithmetical progression as Zhoubi Suanjing (a classic work on astronomy and mathematics written in the first century BC during the Western Han dynasty), Taichu Calendar (enacted in the first year of Taichu, i.e., 104 BC) etc. The data in Yi Wei, being made after Taichu Calendar was carried out and before Sifen Calendar (enacted in 85 AD in the Eastern Han dynasty) was used, might be the final version by arithmetical progression in the history of Chinese astronomy, revealing the scientific level at that time.