THE sources of the information contained in this work are, 1. Official documents; 2. Histories having the sanction of the Pope or of bishops; 3. Scholastic works of the present pontificate, and of recognized authority; 4. Periodicals and journals, avowed organs of the Vatican or of its policy, with books and pamphlets by bishops and other Ultramontane writers; 5. The writings of Liberal Catholics.
Of the official documents the greater part have been officially published. The list of authorities, and the references in each particular case, will sufficiently indicate where these are to be found. Besides these, the Documenta ad Illustrandum of Professor Friedrich are a store of documents of special value, both in themselves and as throwing light upon those officially published. They came into his hands as an official theologian at the Vatican Council, and he published them on his own responsibility. The Sammlung of Friedberg is a vast store, combining the documents of the Vatican with those of Courts, public bodies, and important individuals.
