# Sacred Number

20 Ten fingers and thumbs The fact that humans have eight fingers plus two thumbs must have worked in tens favour, as cultures as various as the Incas, the Indians, the Berbers, the Hittites, and the Minoans all adopted it as the base for their counting systems. Today we all use base ten. Ten is the child of five and two, and unsurprisingly the word ten derives from the IndoEuropean dekm, meaning two hands. Ten is particularly formed as the sum of the first four numbers, one plus two plus three plus four, a fact of profound significance to the Pythagoreans who immortalized it in the figure of the Tetraktys black dots, opposite center and called it Universe, Heaven, and Eternity. As well as being the fourth triangular number, ten is also the third tetrahedral number opposite lower right, a fact that lends it great importance as a simultaneous building number of both two and threedimensional triangular form. Ten lifeinvoking pentagons sit perfectly around a decagon, and DNA, appropriately as the key to the reproduction of life, has ten steps for each turn of its double helix, so appears in cross section as a tenfold rosette opposite, top left. There are ten sephiroth in the Jewish Kabbalahs Tree of Life opposite center and tenfold symmetry was often used in Gothic architecture opposite, top right. Plato believed that the decad contained all numbers, and for most of us today it does, as we can express just about any number we care to in terms of just ten simple symbols. 21