The Story ofSpin. By Sin- Intro Tomonaga. Chicago: U of Chicago P, 1998. Pp. 280. $50.00 Anyone who has been exposed to the rudiments of atomic physics and quantum mechanics knows that the elementary constituents of matter, like the electron and the proton, have a "spin." Just as they carry a unit of electric charge, they also carry a unit of angular momentum. It is as if we can draw a crude analogy between an atom and the solar system: The planets not only orbit around the sun, but also rotate around their own axes, as does the sun. This property of the electron and the proton has enormous practical consequences, too. Without it, permanent magnets would not exist, and MRI technology would not be possible. This book is a fascinating historical and expository narrative by a master narrator Sin-Itiro Tomonaga about important topics related to spin in the context of quantum mechanics. Tomonaga (1906-1979) is a celebratedJapanese theoretical physicist who had firsthand experience in the formative years of quantum mechanics and nuclear physics. The early part of this century was a truly revolutionary period in physics. The Einstein relativity changed our concept of space and time, replaced and extended the Newtonian mechanics to extreme regimes of scale and energy. Quantum mechanics , even more revolutionary than relativity, solved the mysteries of the atomic world and changed our concept of reality. After a quarter-century of groping for makeshift theories and models of quantum phenomena, it developed into the modern quantum mechanics in the latter half of the 1920s with a breathtaking speed, thanks to a handful of heroes who made this possible. Tomonaga was a student in Japan in this period, and he went on to study under Heisenberg, one of the heroes, in the mid-1930s. Together with Yoshio Nishina, his mentor, and Hideki Yukawa, his fellow student and rival-friend, they built the foundations of nuclear physics research inJapan. Both Yukawa and Tomonaga would receive the Nobel Prize later. Tomonaga was a delicate, mild-mannered man. In his private life, he was an oldfashioned Japanese. He relaxed at home wearing a kimono and sipping sake, and he frequented a neighborhood yose (a story-teller's theater). Like a maiden at a spinning wheel, he weaves the story of spin slowly and patiently. It is possible to imagine one's self sitting in a lecture room listening to Professor Tomonaga. He writes out equations and statements on the blackboard carefully and completely in a beautiful style, while he explains every detail in a patient voice, always mixing it with background stories of who discovered what and how, who failed and why, and how they fought each other. In his narrative, there are three true heroes and a supporting cast of a dozen or so. (He also sprinkles his stories with revealing photos of them.) The true heroes are P.A.M. Dirac, Wolfgang Pauli, and Werner Heisenberg. They were all born in this century, and were in their mid-1920s when they did their most celebrated work. Tomonaga's characterization of the heroes is very vivid. Dirac is a true genius, an acrobat, a deus ex machina; his thought process is beyond the comprehension of us mortals, Pauli, a fiercely intolerant perfectionist, applies his standard indiscrimately to himself and others, mincing no words to criticize anything less than perfect in his eyes, and in the process frequently commits the sin of throwing out somebody 's baby together with the water. Heisenberg is a brilliant, energetic, and downto -earth prime mover who excels in playing analogies; he discovered not only matrix 294 I Book Reviews quantum mechanics but also laid the foundations of nuclear physics and ferromagnetism . The book consists of 11 lectures, or let us say 11 stories. It starts with "Before the Dawn," the struggle to come up with a refined and consistent picture of the atom on the basis of the Bohr model of atoms and spectroscopic data. In the second lecture Tomonaga explains how physicists were gradually, and reluctantly, led to the idea of a spinning electron. In the third lecture he introduces Pauli's description of spin, which he had initially rejected...