There is one objection to grouping,—that books can seldom be made to fill any classification exactly, their contents overrunning the classes, so that they must be entered in several places, or they will fail to be found under some of the subdivisions of which they treat. Thus in the chronological arrangement of _History_, whether we arrange by the first date, the average, or the last date of each work, the books cover periods of such various length that one can never get all that relates to one period together. { 94}
There is another objection,—that it is much harder to make a catalogue with subdivisions, which of course require a knowledge of the subject and examination of the books; and the difficulty increases in proportion to the number of the books and the minuteness of the divisions.
256. The subarrangement in groups will often be alphabetical by authors; but in groups or subjects of a historical character it should be chronological, the order being made clear by putting the dates first or by printing them in heavy-faced type.
Thus under countries the division _History_ will be arranged according to the period treated of, the earliest first; so under _Description_, for England as seen by foreigners in the days of Elizabeth was a very different country from the England seen by Prince Pückler-Muskau in 1828, or satirized by Max O’Rell in 1883. So _Statistics_ and _Literature_, and other divisions, should be treated when they are long enough.
257. When there are many cross-references classify them.
_Ex._ «Architecture.» _See also_ «Arches»;—«Baths»;—«Bridges»;—«Cathedrals»;—«Fonts»;—[and many other things built];
_also_ «Carpentry»;—«Drawing»;—«Metal-work»;—«Painting»;—[and many other means or methods of building];
_also_ «Athens»;—«Berlin»;—«Boston»;—«Milan»;—«Rome»;—«Venice»;—«Verona»;—[and many other cities whose buildings are described];
_also_ «Arabia»;—«Assyria»;—«Egypt»;—«France»;—«Greece»;—«India»;—«Italy»;—[and many other countries whose architecture is described].
258. When the titles are numerous under a subject-heading divide them, but avoid subdivision.
It may not be best to adopt strictly the same method in the subdivisions under countries that was recommended for government publications. There are advantages in both the following plans. The second is the dictionary plan pure and simple; the first is a bit of classification introduced for special reasons into a dictionary catalogue, and perhaps out of place there. It is, however, the one which I have adopted for the catalogue of the Boston Athenæum.