Xuan Kong Fei Xing

The mechanism is arithmetical. Nine numbers are placed in a three by three grid, then moved through it in a fixed path, so that each successive arrangement is derived from the one before by the same rule. A building receives a chart determined by when it was built and which way it faces, and further charts are generated for the running period, the year and the month, so the reading of a site changes over time without anything physical about it changing.

The periods it counts by are twenty years long and run in a cycle of nine, which gives a hundred and eighty year cycle made of three sixty year cycles. Time is therefore built into the method at three nested scales, and a practitioner reads the interaction of the fixed chart with the current one rather than either alone.

That is what distinguishes this school from its neighbours. The form school reads the shape of the land, the mountains and watercourses around a site. The compass school reads the bearing of the building. Flying Star reads the two together as they change through time, which is why a house is said to alter in character while standing still. Stephen Skinner's manual of Chinese geomancy sets out the relations between the schools, and Ho Peng Yoke's study of Chinese mathematical astrology places the nine palace arithmetic in the wider family of divinatory systems built on the same numbers.

The grid Flying Star uses is not an arbitrary arrangement. It is the luoshu, the three by three square holding the numbers one to nine in which every row, every column and both diagonals add to fifteen. Chinese tradition receives it as a pattern seen on the shell of a turtle emerging from the river Luo, and it appears across Chinese cosmological writing as the numerical plan of the nine palaces, the eight directions and the centre.

Schuyler Cammann's study of the magic square of three in Chinese philosophy and religion traces how the figure was used and what was claimed for it, and shows that its religious career is older and wider than any single divinatory method built on it. The same square underlies other arts of the same family: the nine palace schemes that Ho Peng Yoke examines in his account of Chinese mathematical astrology use it as their board.

Recognising that inheritance places Flying Star correctly. It is not a self contained system of house reading that happens to use numbers, but one application of a numerical cosmology that Chinese thought had already put to work in ritual, in statecraft and in several kinds of divination. The flying of the stars is the luoshu made to turn, and what a practitioner is reading is a very old diagram in motion.