Ian Stewart shows how equations open new vistas of experience, from electronics and global communications to radar, lasers, space craft and the atom bomb. His narative spans two and a half millennia, from the ancient Greeks to the ... formulation that recently guided the world's banking systems to near-oblivion. He show how insights in one era often inform work centuries later: Pythagoras's theorem inspired [Albert] Einstein and, yet more curiously, the stumbling calculations of a sixteenth century gambler [Girolamo Cardano] led to an impossible number that became a key to the baffling world of quantum physics.