PREFACE
libraries or manuscript-rooms for their courtesy in facilitatin my researches. I am especially indebted to the Prefect of the Vatican Library, the librarian of the venerable monastery of Grotta Ferrata, the authorities of the Vallicelliana, Laurenziana, and Riccardiana, Signore Levi of the Marciana, and M. Omont of the National Library. The heads of the Court Library at Vienna, the University Library at Leipzip, and the University Library at Messina have kindly permitted me to have photographs taken of manuscripts in their respective collections. The time is gone by for thanking the late Prefect of the Ambrosian Library. Let me at least say that I count it among the happiest results for me of these studies to have seen and spoken with Antonio Ceriani.
