the book
number, and so does not increase the number of digits as would at first
appear.

Parts of sets, and books on the same or allied subjects, are never
separated as they are sure to be, sooner or later, in every library
arranged on the common plan, unless it be frequently re-arranged and
re-catalogued. The great expense of this re-cataloguing makes it
impracticable except for a few very wealthy libraries. In this system
the catalogue and book numbers remain unchanged through all changes of
shelving, buildings, or arrangement. In addition to its own peculiar
merits, this plan has all the advantages of the card catalogue principle
and of the relative location, which have been used and very strongly
approved by prominent libraries.

As in the card catalogue system, there is room for indefinite expansion
without devices or provisions. Space is the only requisite and if the
shelf room is exhausted, the floor space is equally good, except for the
inconvenience of stooping.

Some prominent opponents of classed catalogues have admitted that the
Subject Index, in deciding where to class a book at first, and where to
look for it ever afterwards, has removed their strongest objections.
Certainly it would be impossible to make an Index more cheaply or more
easy of reference, it being a single alphabet, of single words, followed
by single numbers.

These class numbers applied to pamphlets have proved specially
satisfactory. The number is written on the upper left corner and the
pamphlets are arranged either in pamphlet cases with the books on
the same subject or on special shelves divided every decimeter by
perpendicular sections. As each pamphlet is examined when received into
the library, it is the work of a single moment to pencil on it its
class number. There is no expense whatever incurred, and yet the entire
pamphlet resources of the library on any subject can be produced almost
instantly. The immense advantages of this plan over those in common use,
both in economy and usefulness, will be appreciated by every librarian
caring for a pamphlet collection. A catalogue of authors may be made
on slips if desired. The pamphlets themselves are the best Subject
Catalogue.

Though designed wholly for library use, the plan has proved of great
service in preserving newspaper clippings in large envelopes arranged
by class numbers; and more especially in taking the place of the common
note-book and Index Rerum. Slips of unifor