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that the time is opportune for pushing vigorously in every country the construction of a general catalogue of historical documents, we may indicate a palliative: it is important that scholars and historians, especially novices, should be accurately informed of the state of the instruments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.
But scholars and historians often need, in respect of documents, information not usually supplied by descriptive catalogues; they wish, for example, to know whether such and such a document is known or not, whether it has already been critically dealt with, annotated, or utilised. This information can only be found in the works of former scholars and historians. In order to become acquainted with these works, recourse must be had to those "bibliographical repertories," properly so called, of all kinds, compiled from very different points of view, which have already been published. Among the indispensable instruments of Heuristic must thus be reckoned bibliographical repertories of historical literature, as well as repertories of catalogues of original documents.
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