Other and later laborers are such as Cardinal Thomasius (Rome, 1741), who follows upon the traces of George Cassander, the Liberal Catholic (Paris, 1616). We are possibly more indebted to Cassander than to Thomasius for the correct designation of a good deal of the authorship. Both of these editors collate the text with other versions, and thus prepare the way for later and more accurate work. Both depend to a notable degree upon the book of George Fabricius (Basle, 1564), which is quite rare; although Thomasius’ works are said by Daniel to be sufficiently uncommon in Germany, as they certainly are in America. The recent republication of the Mozarabic Breviary in J. P. Migne’s _Patrologia_ brings this volume, however, within easy reach. Thus we are naturally led to speak of the sources of the hymns themselves—sources from which these editors have secured them. As a part of religious worship they were incorporated into the various breviaries, of which hundreds must have been in use before the unification begun by the Church of Rome in the sixteenth century. Besides these church books, there were collections of hymns alone made by mediaeval schools, whose manuscripts still exist in European libraries. The only method by which to ascertain the number and extent of these treasures was to gather and classify them. And strangely enough this labor has been performed by Protestants rather than by Catholics. Cassander’s book was forbidden at Rome, as he was what now would be called an Old Catholic; Luther, George Fabricius, and Hermann Bonn were in no better odor of sanctity; and for our own times the standard work is that of Herman Adelbert Daniel, who was a Lutheran professor at Halle, while close behind him come several others of the same religious belief. The necessary and highly difficult task of getting the materials together has been exhaustively performed. Professor Daniel’s investigations extended to the original copies in monasteries and abbeys almost without number. But F. J. Mone enlarged even upon this. Daniel’s _Thesaurus_ in five volumes was completed in 1856—having been several years in course of publication—and it stands as yet unrivalled. Mone’s _Lateinische Hymnen des Mittelalters_ appeared in 1853-55, and was therefore available for the conclusion of Daniel’s great work. Its value consists in the fact that it is derived exclusively from manuscripts and from material hitherto untouched. The Germans, indeed, have made Latin hymnology a special branch of study, considering that it is profitable to them for its value religiously and historically. From old Flacius Illyricus’ appendix to the _Catalogus Testium Veritatis_ has been recovered the original of Bernard of Cluny’s “Jerusalem the Golden”—a poem which would never have been known by us if this same Matthias Flacius had not preserved it as a testimony against the corrupt state of the Church.