133
chambers or tanks. The most famous of the early clocks was constructed in the then national capital, Kaifeng, about the time of the Norman Conquest of Britain, by Su Song [1020 - 1101 AD]. Su Song, born in Tongan county in Fujian province where he is still revered within the Su ancestral hall, created an astronomical clocktower in which he incorporated his mechanical clock, a celestial globe and an armillary sphere. The difference between water clocks until the time of Su Song and his invention was his creation of an escapement mechanism which controlled the regular movement of the small water tanks providing previously unheard of accuracy.
The Twenty-eight Constellations
In early China the visible stars were divided into 28 zones or constellations, referred to as lunar mansions. These provided manageable proportions of the heavens, with seven in each of the four directions. The selection of twenty-eight reflects the time it takes the moon to make a complete circuit of the stars, a fraction under twenty-eight days. Books describing such celestial spirits, printed in Taiwan, illustrate each spirit with a sketch showing the "human" form and giving its attributes. Although usually regarded as a group, in some places a number of these celestial spirits, always mythological, are referred to individually in legend or by ritual specialists. According to religious specialists each of the stellar deities of the Twenty-eight Constellations has a title and a specific role, the latter differing depending upon the individual ritual specialists or books.
The Pole Star was also the celestial base of the several deities, the main one being the Northern Emperor, also known as the Dark Warrior, Xuan Wu, one of the spirits of great antiquity who ruled one quarter of the universe. Each of the Thirty-six stars of the Plough was a legendary hero recorded in one of the numerous stories of the deification of and struggles between the deities. They are deities of good omen, whereas the Seventy-two Stars of ill-omen, without individual legends, are just that, stellar spirits of bad luck. The great popularity of the Northern Emperor has rested for many centuries on devotees' belief in the mighty magical powers with which he suppresses demonic forces with his Daoist Pole Star sect, Beiji Pai, of which he is the patron, centred at Wudang Shan in Hubei. Xuan Wu was the Lord of the northern sector of the 28 Lunar Mansions and as one of the Spirits of the Four