determines its place. Following this rule, a Philosophy of Art is
put with Art, not with Philosophy; a History of Mathematics, with
Mathematics, not with History; for the philosophy and history are simply
the _form_ which these books have taken. The true content or subject is
Art, and Mathematics, and to the student of these subjects they are most
useful. The predominant tendency or obvious purpose of the book, usually
decides its class number at once; still many books treat of two or more
different subjects, and in such cases it is assigned to the place where
it will be most useful, and underneath the class number are written the
numbers of any other subjects on which it also treats. These _Cross
References_ are given both on the plate and the subject card as well
as on the cross reference card. If a book treats of a majority of the
sections of any division, it is given the Division number instead of the
most important Section number with cross references.

Collected works, libraries, etc., are either kept together and assigned
like individual books to the most specific head that will contain them;
or assigned to the most prominent of the various subjects on which they
treat with cross references from the others; or are separated and the
parts classed as independent works. Translations are classed with their
originals.

The Alphabetical Subject Index is designed to guide, both in numbering
and in finding the books. In numbering, the most specific head that will
contain the book having been determined, reference to that head in the
Index will give the class number to which it should be assigned. In
finding books on any given subject, reference to the Index will give the
number under which they are to be sought on the shelves, in the Shelf
Catalogue, or in the Subject Catalogue. The Index gives after each
subject the number of the class to which it is assigned. Most names of