=258. Annotation, etc.=--In all forms of catalogue the difficulties which have to be obviated are the lack of clearness of meaning in titles and of information as to the qualifications of authors, the scope, size, _format_, date and other features of books. These particulars can, and should, be given as a rule under the principal entry of each book as part of the main entry; but to amplify such information, notes--technically called annotations--are now frequently provided. An admirable conspectus of the art of annotation is available in E. A. Savage’s _Manual of Annotation in Library Catalogues_, and the student is referred to that work. Here it will be sufficient to say that catalogue entries should be as full in bibliographical particulars as the means of the library will allow, and that notes, which must be as brief as possible, should elucidate obscure titles, show the qualifications of the author, his method, elementary or otherwise, the preliminary knowledge required for the reading of the book, its place in the literature of the subject, and the presence of bibliographies, glossaries, etc.; and should give, in the case of reprints, the date of first publication, and in that of revised editions, the nature of the revision or editorial additions. =259. Form of Catalogue.=--Having chosen the manner in which his catalogue is to be compiled, or, to adapt a term from classification, its inner form, the librarian has an almost equally important decision to make as to the manner of its outer form, or the way in which it may be made accessible to his public. At one time every librarian aimed to produce a printed catalogue as a matter of course and necessity, partly because MS. forms were imperfect, and partly because the universal prevalence of the barrier system made a key of which every reader could have a copy an integral part of the charging. This view does not prevail to anything like the former extent, and the complete printed catalogue in book form is becoming less and less general. In some ways this is unfortunate, because the printed catalogue has the indisputable value of book-form, homogeneity, and convenience both for consultation and for carrying about; besides, it is a valuable bibliographical tool for use in all other libraries. At the same time, the great cost of the printed catalogue, especially when issued complete in any of the alphabetical forms, and the irritating fact that in a growing library it is incomplete the day after it is published, have made it almost impossible for public librarians to publish in this form. Complete printed class-lists are a more satisfactory form, because each class can be published separately and at such intervals as will distribute the cost over several years; and revisions can be made in similar serial manner, so that classes such as the Useful Arts, in which books most rapidly run out of date or are superseded, can be more frequently revised than others.