Giordano Bruno and the Hermetic Tradition purports to trace the history of Hermeticism from the time a Greek manuscript of the so-called Corpus Hermeticum was brought to Florence in 1453, at the time of the fall of Constantinople to the Turks. At the behest of Cosimo de Medici it was soon translated into Latin by Marsilio Ficino, one of few Italians who had studied Greek. The Corpus is a collection of mystical tracts in the form of dialogues, hymns, dream visions, prayers, and scripture-like accounts which are now understood to have been written by various persons during the early Middle Ages, but at the time of their introduction into Renaissance Italy, they were believed to be by Hermes Trismegistus who, again according to belief at the time had lived contemporaneously with Moses, but was later determined to be a mythical character who possibly had never lived at all. This little collection of tracts, which had much in common with the Neoplatonic philosophy that was already widely accepted, had an electrifying effect on many of the learned men who fell under its spell, and it set off an amazing train of events which may have indirectly influenced the development of science and mathematics leading up to and during the Enlightenment.What was the excitement all about? As a supposed contemporary of Moses, Hermes' writings were believed to foretell Christ much as the Hebrew Bible did. This was important to the intellectuals who saw the Church as more a purveyor of corruption and authoritarianism rather than as a fount of morality and spirituality. Since the Church was not a source of spiritual sustenance, those with a spiritual hunger were willing to seek nourishment wherever it lay, and they attempted to reconcile Hermeticism with Christianity in an effort to stay within the good graces of the Church.The Corpus Hermeticum was a deeply spiritual collection of texts. However, it was not the first Hermetic document known to Renaissance scholars. An earlier medieval Latin manuscript called the Picatrix had been circulating down through the ages. It was largely a text of magical or theurgical procedures. While the Renaissance sages like Ficino were steeped in astrology, they steered clear of outright magic because of the stance of the Church which was burning people at the stake for heresy. Magic definitely fell under the heading of heresy.Thus there were two kinds of Hermeticism: one gnostic and spiritual in the tradition of the Corpus Hermeticum and the other occult and magical following more in the tradition of the Picatrix. Frances Yates traces the history of magical Hermeticism from Ficino and Pico della Mirandola to Cornelius Agrippa, Giordano Bruno, Thomas Campanella and Robert Fludd. Each of these individuals put his own individual mark on the theory and practice of Renaissance magic.The first half of the book provides background on Hermeticism. The second focuses on Bruno and the aftermath of the discovery by philologist Lorenzo Valla that the Corpus Hermeticum did not trace back to the era of Moses after all but was written and compiled somewhere around the second or third century A.D.After crawling through four hundred pages of history and historiography, the real payoff comes in the final chapter where Yates credits not the practitioners but their critics with hastening the development of science and mathematics. It is Yates' position that the level of analysis achieved prepared the way for more and more rigorous thought processes. For example, Bruno was a believer in the Copernican theory of heliocentricity, but his belief came through a version of Pythagorean numerology. Copernicus and his follower Johann Kepler used actual astronomical observations and pure mathematics to reach their own conclusions. The trend toward pure mathematics led to Descartes and all that followed. The condemnation of Bruno to burn at the stake has been attributed to his belief in Copernican heliocentricity. But there was much more to it than that.Only the most dedicated reader will want to slog through this entire book. I almost quit halfway through. The more it concentrated on magic, the more my interest waned. But in the end, I would have to give this book the highest marks both for what it explains, for the clarity of the narrative — except for all the irritating untranslated Latin quotations — and for the conclusions it reached, which shed important light on the history of science.