Shu Ching. The Canon of Yao/The Canon of Shun, Chapter 2.
2. He commanded the Hsis and Hos, in reverent accordance with (their observation of) the wide heavens, to calculate and delineate (the movements and appearances of) the sun, the moon, the stars, and the zodiacal spaces, and so to deliver respectfully the seasons to be observed by the people.
He separately commanded the second brother Hsi to reside at Yü-i, in what was called the Bright Valley, and (there) respectfully to receive as a guest the rising sun, and to adjust and arrange the labours of the spring. 'The day,' (said he), 'is of the medium length, and the star is in Naio; you may thus exactly determine mid-spring. The people are dispersed (in the fields), and birds and beasts breed and copulate.'
He further commanded the third brother Hsi to reside at Nan-chiao, (in what was called the Brilliant Capital), to adjust and arrange the transformation of the summer, and respectfully to observe the exact limit (of the shadow). 'The day' (said he), 'is at its longest, and the star is in Huo; you may thus exactly determine mid-summer. The people are more dispersed; and birds and beasts have their feathers and hair thin, and change their coats.'
He separately commanded the second brother Ho to reside at the west, in what was called the Dark Valley, and (there) respectfully to convoy the setting sun, and to adjust and arrange the completing labours of the autumn. 'The night' (said he), 'is of the medium length, and the star is in Hsü; you may thus exactly determine mid-autumn. The people feel at ease, and birds and beasts have their coats in good condition.'
He further commanded the third brother Ho to reside in the northern region, in what was called the Sombre Capital, and (there) to adjust and examine the changes of the winter. 'The day' (said he), 'is at its shortest, and the star is in Mao; you may thus exactly determine mid-winter. The people keep in their houses, and the coats of birds and beasts are downy ad thick.'
The Ti said, 'Ah! you, Hsis and Hos, a round year consists of three hundred and sixty-six days. Do you, by means of the intercalary month, fix the four seasons, and complete (the period of) the year. (Thereafter), the various officers being regulated in accordance with this, all the works (of the year) will be fully performed.'
Text source: Shu Ching, The Book of History. Translated by James Legge