The Chinese hexagrams are based on a cosmic formula of change. Out of the Unknown Principle arise two principles Yang and Yin, positive and negative, expansive and contractive; and all cycles are considered as the time-symbols of the interaction of these two principles. They are particularly related to the cycles of the year, Yang dominating at the summer solstice, Yin, at the winter solstice. Yang is represented by a straight line, Yin, by a line broken in two. The hexagrams constitute the 64 possible combinations made by the six-fold superposition of these lines. Each is referred thus to a section of the yearly cycle, and carries a symbol which has significance in terms of that section. Each hexagram is thus a sort of zodiacal sign, or cosmic viewpoint measured on the circumference of the orbit of the Earth. The symbols themselves were apparently written down by King Wen around the year 1100 or 1000 B.C.; but it could undoubtedly be shown that their symbolism is based on “holistic logic,” just as astrological symbolism.