The imperfection of descriptive catalogues has consequences which deserve our attention. On the one hand, we can never be sure that we have exhausted all the sources of information; who knows what may be held in reserve by the uncatalogued collections?[37] On the other hand, in order to obtain the maximum amount of information, it is necessary to be thoroughly acquainted with the resources furnished by the existing literature of Heuristic, and to devote a great deal of time to preliminary researches. In point of fact, every one who proposes to collect documents for the treatment of a point of history begins by consulting indexes and catalogues.[38] Novices set about this important operation so slowly, with so little skill, and with so much effort, as to move more experienced workers to mirth or pity, according to their disposition. Those who find amusement in watching novices stumble and strain and waste their time in the labyrinth of catalogues, neglecting those which are valuable, and thoroughly exploring those which are useless, remember that they also have passed through similar experiences: let every one have his turn. Those who observe with regret this waste of time and strength consider that, while inevitable up to a certain point, it serves no good purpose; they ask whether something might not be done to mitigate the severity of this apprenticeship to Heuristic, which at one time cost them so dear. Besides, is not research, in the present condition of its material aids, difficult enough whatever the experience of the researcher? There are scholars and historians who devote the best part of their powers to material searches. Certain branches of historical work, relating chiefly to mediæval and modern subjects (the documents of ancient history are fewer, have been more studied, and are better catalogued than the others), imply not merely the assiduous use of catalogues, not all furnished with indexes, but also the personal inspection of the whole contents of immense collections which are either badly catalogued or not catalogued at all. Experience proves beyond a doubt that the prospect of these long searches, which must be performed before the more intellectual part of the work can be begun, has deterred, and continues to deter, men of excellent abilities from undertaking historical work. They are, in fact, confronted with a dilemma: either they must work on a supply of documents which is in all probability incomplete, or they must spend themselves in unlimited searches, often fruitless, the results of which seldom appear worth the time they have cost. It goes against the grain to spend a great part of one's life in turning over catalogues without indexes, or in passing under review, one after another, all the items which go to form accumulations of uncatalogued _miscellanea_, in order to obtain information (positive or negative) which might have been obtained easily and instantaneously if the collections had been