classes, but great confusion will be caused by uniting the three systems. The alphabetical arrangement is so simple, convenient and easily understood that it has naturally superseded the other forms, save in some exceptional cases. Much of the value of an index depends upon the mode in which it is printed, and every endeavour should be made to set it out with clearness. In old indexes the indexed word was not brought to the front, but was left in its place in the sentence, so that the alphabetical order was not made perceptible to the eye. There are few points in which the printer is more likely to go wrong than in the use of marks of repetition, and many otherwise good indexes are full of the most perplexing cases of misapplication in this respect. The oft-quoted instance,

actually occurred in a catalogue. But in modern times there has been a great advance in the art of indexing, especially since the foundation in 1877 in England of the Index Society; and the growth of great libraries has given a stimulus to this method of making it easy for readers and researchers to find a ready reference to the facts or discussions they require. Not only has it become almost a sine qua non that any good book must have its own index, but the art of indexing has been applied to those books which are really collections of books (such as the Encyclopaedia Britannica), to a great newspaper like the London Times, and to the cataloguing of great libraries themselves. The work in these more elaborate cases has been enormously facilitated by the modern devices by means of which separate cards are used, arranged in drawers and cases, American enterprise in this direction having led the way. And the value of the work done in this respect by the Congressional Library at Washington, the British Museum and the London Library (notably by its Subject Index published in 1909) cannot well be exaggerated. (See also Bibliography).

INDEX LIBRORUM PROHIBITORUM, the title of the official list of those books which on doctrinal or moral grounds the Roman Catholic Church authoritatively forbids the members of her communion to read or to possess, irrespective of works forbidden by the general rules on the subject. Most governments, whether civil or ecclesiastical, have at all times in one way or another acted on the general principle that some control may and ought to be exercised over the literature circulated among those under their jurisdiction. If we set aside the heretical books condemned by the early councils, the earliest known instance of a list of proscribed books being issued with the authority of a bishop of Rome is the Notitia librorum apocryphorum qui non recipiuntur, the first redaction of which, by Pope Gelasius (494), was subsequently amplified on several occasions. The document is for the most part an enumeration of such apocryphal works as by their titles might be supposed to be part of Holy Scripture (the “Acts” of Philip, Thomas and Peter, and the Gospels of Thaddaeus, Matthias, Peter, James the Less and others).1 Subsequent pontiffs continued to exhort the episcopate and the whole body of the faithful to be on their guard against heretical writings, whether old or new; and one of the functions of the Inquisition when it was established was to exercise a rigid censorship over books put in circulation. The majority of the condemnations were at that time of a specially theological character. With the discovery of the art of printing, and the wide and cheap diffusion of all sorts of books which ensued, the need for new precautions against heresy and immorality in literature made itself felt, and more than one pope (Sixtus IV. in 1479 and Alexander VI. in 1501) gave special directions to the archbishops of Cologne, Mainz, Trier and Magdeburg regarding the growing abuses of the printing press; in 1515 the Lateran council formulated the decree De Impressione Librorum, which required that no work should be printed without previous examination by the proper ecclesiastical authority, the penalty of unlicensed printing being excommunication of the culprit, and confiscation and destruction of the books. The council of Trent in its fourth session, 8th April 1546, forbade the sale or possession of any anonymous religious book which had not previously been seen and approved by the ordinary; in the same year the university of Louvain, at the command of Charles V., prepared an “Index” of pernicious and forbidden books, a second edition of which appeared in 1550. In 1557, and again in 1559, Pope Paul IV., through the Inquisition at Rome, published what may be regarded as the first Roman Index in the modern ecclesiastical use of that term (Index auctorum et librorum qui tanquam haeretici aut suspecti aut perversi ab Officio S. R. Inquisitionis reprobantur et in universa Christiana republica interdicuntur). In this we find the three classes which were to be maintained in the Trent Index: authors condemned with all their writings; prohibited books, the authors of which are known; pernicious books by anonymous authors. An excessively severe general condemnation was applied to all anonymous books published since 1519; and a list of sixty-two printers of heretical books was appended. This excessive rigour was mitigated in 1561. At the 18th session of the council of Trent (26th February 1562), in consideration of the great increase in the number of suspect and pernicious books, and also of the inefficacy of the many previous “censures” which had proceeded from the provinces and from Rome itself, eighteen fathers with a certain number of theologians were appointed to inquire into these “censures,” and to consider what ought to be done in the circumstances. At the 25th session (4th December 1563) this committee of the council was reported to have completed its work, but as the subject did not seem (on account of the great number and variety of the books) to admit of being properly discussed by the council, the result of its labours was handed over to the pope (Pius IV.) to deal with as he should think proper. In the following March accordingly were published, with papal approval, the Index librorum prohibitorum, which continued to be reprinted and brought down to date, and the “Ten Rules” which, supplemented and explained by Clement VIII., Sixtus V., Alexander VII., and finally by Benedict XIV. (10th July 1753), regulated the matter until the pontificate of Leo XIII. The business of condemning pernicious books and of correcting the Index to date has been since the time of Pope Sixtus V. in the hands of the “Congregation of the Index,” which consists of