the three worlds in the harmony of the universe. This final application would alone demonstrate the--in some way--magic virtue of the _Tetragram_ in the order of ideas. In it was found not only the principles of the sciences, the law of beings and their mode of evolution, but also the very reason of the different religions and their superior unity. This was in reality the universal key. Hence the enthusiasm with which Lysis speaks of it in the _Golden Verses_; one can now understand why the Pythagoreans swore by this great symbol: “I swear it by him who has transmitted into our souls the Sacred Quaternion, the source of nature, whose cause is eternal.” Pythagoras carried a great deal farther the teaching of numbers. In each of them he defined a principle, a law, an active force of the universe. He said, however, that the essential principles are contained in the first four numbers, since all the others are formed by adding or multiplying them. In the same way the infinite variety of beings composing the universe is produced by the combinations of the three primordial forces: matter, soul, spirit, under the creating impulse of the divine unity which mingles and differentiates, concentrates and separates. Along with the chief masters of esoteric science Pythagoras attached great importance to the numbers seven and ten. _Seven_, the compound of three and four, signifies the union of man and divinity. It is the figure of the adepts, of the great initiates, and, since it expresses the complete realization in all things through seven degrees, it represents the law of evolution. The _number ten_ formed by the addition of the first four numbers, and containing the former number, is the perfect number, _par excellence_, for it represents all the principles of divinity, evolved and re-united in a new unity. On finishing the teaching of his theogony, Pythagoras showed his disciples the nine Muses, personifying the sciences, grouped three by three, presiding over the triple ternary evolved in nine worlds, and forming, along with Hestia, the divine science, guardian of the primordial Fire--_the sacred Decad_. THIRD DEGREE--PERFECTION[15] _Cosmogony and psychology.--The evolution of the soul._