The learned author of this volume is well known, and deservedly esteemed, by a very wide circle of appreciative students of ecclesiastical history. His honesty and trustworthiness in publishing the results of his laborious investigations earned for him the praise and encouragement of Pope Leo XIII.<br><br>In the hope that this short treatise may be of service in an English version, I have ventured to translate it, and for his permission to me to undertake this work I must express my thanks to Monsignor Duchesne.