A scholarly survey of how the concept of ``secret'' assisted the development of experimental science from ancient times until the 17th century. The idea of delving into the hidden things of nature and harnessing--or even altering--its processes smacked, in centuries past, more of magic than of science. Eamon (History/New Mexico State Univ.) opens with a nuanced view of the medieval tradition of secrets, its Hellenistic origins, and its Islamic and Scholastic forms. He notes that the empirical approach was not regarded as ``science'' because, rather than being purely theoretical, it dealt with the unpredictable and the ``irrational.'' Eamon looks at attitudes toward science of, among others, St. Augustine, Albert the Great, and Thomas Aquinas. Eamon is much influenced by Elizabeth Eisenstein's work on the role of printing in exposing classical scientific ideas to scrutiny. He relates how craft knowledge, traditionally kept secret, was divulged by means of vernacular technical textbooks, which contained ``recipes'' and resembled modern how-to books. In 16th-century Italy, ``professors of secrets'' arose who traveled and published practical and ``alternative'' medical advice based on herbs and potions. We encounter colorful characters: Leonardo Fioravanti, a surgeon who, without antisepsis or anesthesia, took out a woman's spleen, ``though up to that time I had never taken out anything''; the great magus Giambattista Della Porta, who employed occult practices in a purely empirical manner, i.e., without the incantations. In the final section of his book, Eamon describes how this dissemination of knowledge led to the beginnings of the modern empirical attitude, which, he suggests, appealed more to the bourgeois values of the time than did the holistic theoretical concerns of earlier centuries. A feast of detailed scholarship, anecdote, and reflections- -touching on a crucial but neglected theme in the development of the western intellectual tradition.