New books as received are numbered and put into place, in the same way
that new titles are added to the card catalogue.

The single digit occasionally prefixed to the book number, e.g. the 3 in
421-3-7 is the nearest height in decimeters of books too large to be put
on the regular library shelves, which are only 2-1/2 decimeters apart.
The great mass of the library consists of 2-decimeter books, the size
numbers of which are omitted. Books from 2-1/2 to 3-1/2 decimeters in
height have 3 prefixed to the book number, and are found on the bottom
shelf of each range. The larger sizes are prefixed with 4, 5, &c., and
are found on the special shelves provided, in order to avoid the great
waste of space otherwise occasioned by the relative location. By this use
of the size numbers a close economy of space is secured.

Thus all the books on any given subject are found standing together, and
no additions or changes ever separate them. Not only are all the books on
the subject sought, found together, but the most nearly allied subjects
precede and follow, they in turn being preceded and followed by other
allied subjects as far as practicable. Readers not having access to the
shelves find the short titles arranged in the same order on the Shelf
Catalogue, and the full titles, imprints, cross references, notes, &c.,
on the Subject Catalogue. The uncatalogued pamphlets treating of any
subject bear the same class number and are arranged on the shelves
immediately after the books of each section.

In both the Authors' Catalogue and the Subject Index, brevity has been
studied because of the economy, but more because of the much greater
ease of reference to a short title catalogue. The custom of giving full
titles, etc., under authors, and only references or very brief titles
under subjects, has been reversed. A reader seeking a book of a _known