Inscriptionum Latinarum_ will have been produced in less than fifty years. The results obtained by the Bollandists and the Imperial Academy of Vienna are not less conclusive. Assuredly nothing is now lacking, except funds, to secure the speedy endowment of historical study with the indispensable instruments of research. The methods employed in the construction of these instruments are now permanently fixed, and it is an easy matter to recruit a trained staff. Such a staff must evidently be largely composed of keepers of archives and professional librarians, but it would also contain unattached workers with a decided vocation for the construction of catalogues and indexes. Such workers are more numerous than one would at first be inclined to think. Not that cataloguing is easy: it requires patience, the most scrupulous attention, and the most varied learning; but many minds are attracted by tasks which, like this, are at once determinate, capable of being definitely completed, and of manifest utility. In the large and heterogeneous family of those who labour to promote the progress of historical study, the makers of descriptive catalogues and indexes form a section to themselves. When they devote themselves exclusively to their art they acquire by practice, as one might expect, a high degree of dexterity. While waiting for the fact to be clearly recognised that the time is opportune for pushing vigorously in every country the construction of a general catalogue of historical documents, we may indicate a palliative: it is important that scholars and historians, especially novices, should be accurately informed of the state of the instruments of research which are at their disposal, and be regularly apprised of any improvements that from time to time may be made in them. Experience and accident have been for a long time trusted to supply this information; but empirical knowledge, besides being costly, as we have already pointed out, is almost always imperfect. Recently the task has been undertaken of constructing catalogues of catalogues--critical and systematic lists of all the catalogues in existence. There can be no doubt that few bibliographical enterprises have possessed, in so great a degree, the character of general utility.