Based on the practical needs of agriculture, Chinese people initiated the 24 solar terms towards the end of the Warring States Period (475 B.C.-221 B. C.). The term "solar terms" can be found in Yellow Emperor' s Canon of Internal Medicine. In this book, every five days was called a hou, and every three hou made a qi. Therefore, a year was divided into 72 hou, or 24 qi. But the names for these solar terms did not appear until the Western Han Dynasty (206 B.C.-24 A. D.) in Huainanzi.