What has thus far been said, offers a partial solution of another current error. The Index is not a studiously selected, not even a systematically arranged catalogue of objectionable books. It was the need of the moment, doctrinal blunders, cavillations and heresies, grievous trespasses against discipline and charity, proceeding from animosity or want of tact, that caused the insertion of most of the books. In nearly all cases the Roman authorities confine themselves to books concerning which they are appealed to; and as there is no system in the making of these appeals, there can be no system in the condemnations. In the new Leonine edition of the Index the books are enumerated alphabetically by authors or pseudonyms; anonymous books are listed according to titles. It must now be obvious to the attentive reader why most of the books put on the Index are works on theology, or on the history and government of the Church, and why (as may be expected in the case of such publications), a considerable percentage are written in Latin. However, a goodly number of books are on the Index because they are detrimental to good morals. There are very few there which treat of the natural sciences. The Index will not busy itself with publications on electricity or X-rays, unless an author on a subject of this sort devote a considerable part of his work to attacks upon religion. There are some well-meaning people who, while agreeing that the productions of Zola, Dumas and other writers of the same sort, fully deserve condemnation, cannot understand why works like Ranke’s _History of the Popes_, which is an acknowledged authority in its line, should be proscribed. Such works are not on the Index for the good things they contain, but for the poison they mix with the wholesome food so cleverly that it takes more than ordinary scholarship and discretion to separate the one from the other. The Roman Committee of Cardinals, which has charge of this part of ecclesiastical discipline, is not at all bent on proscribing books. Works like the one mentioned are never put on the Index unless it is quite clear that the mischief to be feared from them will far outweigh the good they may do. Scholars and students well grounded in their faith, who have a real and legitimate cause for reading a forbidden book can easily obtain a dispensation. It is clear from the preceding explanations that a book may sometimes be dropped from the Index. This is done when a book has long ceased to be dangerous, or a cause of dissension, or if it has fallen into oblivion. Thus Pope Leo XIII caused to be expunged about a thousand titles. This does not imply a reproach for the authorities of former centuries, much less the giving up of an iota of the old principles. 6. Duties Imposed by Law and by Nature.