WORK IS IN FRENCHThis book is a reproduction of a work published before 1920 and is part of a collection of books reprinted and edited by Hachette Livre in the framework of a partnership with the National Library of France providing the opportunity to access old and often rare books from the BnFampampamp39s heritage funds. The works in this collection have been digitized by the BnF and are presented on Gallica its digital library.By reviving these works through a collection of books reprinted on demand we give everyone the opportunity to participate in the transmission of knowledge which is sometimes difficult to access.We have tried to reconcile the faithful reproduction of an old book from its digitalized version with the concern of an optimal reading comfort.