This book aims to treat the history of magic and experimental science and their relations to Christian thought during the first thirteen centuries of our era, with especial emphasis upon the twelfth and thirteenth centuries. No adequate survey of the history of either magic or experimental science exists for this period, and considerable use of manuscript material has been necessary for the medieval period. Magic is here understood in the broadest sense of the word, as including all occult arts and sciences, superstitions, and folk-lore. I shall endeavor to justify this use of the word from the sources as I proceed. My idea is that magic and experimental science have been connected in their development; that magicians were perhaps the first to experiment; and that the history of both magic and experimental science can be better understood by studying them together. I also desire to make clearer than it has been to most scholars the Latin learning of the medieval period, whose leading personalities even are generally inaccurately known, and on perhaps no one point is illumination more needed than on that covered by our investigation. The subject of laws against magic, popular practice of magic, the witchcraft delusion and persecution lie outside of the scope of this book.[4] [Sidenote: Period covered.] At first my plan was to limit this investigation to the twelfth and thirteenth centuries, the time of greatest medieval productivity, but I became convinced that this period could be best understood by viewing it in the setting of the Greek, Latin, and early Christian writers to whom it owed so much. If the student of the Byzantine Empire needs to know old Rome, the student of the medieval church to comprehend early Christianity, the student of Romance languages to understand Latin, still more must the reader of Constantinus Africanus, Vincent of Beauvais, Guido Bonatti, and Thomas Aquinas be familiar with the Pliny, Galen, and Ptolemy, the Origen and Augustine, the Alkindi and Albumasar from whom they drew. It would indeed be difficult to draw a line anywhere between them. The ancient authors are generally extant only in their medieval form; in some cases there is reason to suspect that they have undergone alteration or addition; sometimes new works were fathered upon them. In any case they have been preserved to us because the middle ages studied and cherished them, and to a great extent made them their own. I begin with the first century of our era, because Christian thought begins then, and then appeared Pliny’s _Natural History_ which seems to me the best starting point of a survey of ancient science and magic.[5] I close with the thirteenth century, or, more strictly speaking, in the course of the fourteenth, because by then the medieval revival of learning had spent its force. Attention is centred on magic and experimental science in western Latin literature and learning, Greek and Arabic works being considered as