نبذه عن الكتاب: This book owes much to Jean-Claude Gardin: over the years his aid and indulgence have made my research possible. My gratitude goes also to those whose assistance has been precious to me: Catherine Perl`es, Yves Coppens, Jacques Perriault, Henri-Paul Francfort, Jean Chavaillon, Arnold Lebeuf. Tim Murray, Suzan Murray and Nathan Schlanger kindly agreed to read through the manuscript and help to improve its final version. The research presented here has been carried out with the financial assistance of the Foundation Fyssen and the Foundation Singer-Polignac