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2Public Libraries in the United States. 
  It is one of the marked advantages of the plan that these cross-ref- 
  erences, notes, etc., may be added from time to time, as found conven.
  lent. It is necessary at first to find only the predominant tendener 
  of the book, in order to catalogue it. It extreme care were taken to 
  avoid mistakes, it might be well to keep books very difficult to class
  arranged by themselves for a time till read or carefully examined by 
  some one competent to decide their true place. Cross-references are 
  added when they are found necessary. After reading, a volume of 
  sermons may be found to be aimed at the doctrine of evolution, though 
  this fact was not noticed in classing. When it is found, however, the 
.evolution number, 575, is written under the religion-and-science.sermoi
number, 255, and ever after a reader knows at once by this number the 
tendency of the volume. It is designed to add these numbers indi- 
eating more closely the character of the book as rapidly as possible, and
specialists are invited to call the attention of the librarian to every de.
sirable cross-reference they notice in their reading. These numbers take
but little room, are easily added, and in most cases are valuable. 
   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 number. 
 ing 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 as- 
 signed. In finding books on any given subject, reference to the index 
 will gi-e the number under which they are to be sought on the shelv-es,
 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 countries, towns, animals, plants, minerals, diseases, etc., have
 been omitted, the aim being to furnish an index of subjects on which 
 books are written, and not a gazetteer or a dictionary of all the nouns
 in the language. Such subjects will be found as special chapters or 
 sections of books on the sutbjects given in the index. The names of 
 individuals will be found in the Class List of Biography. Omissions of 
 any of the more general subjects will be supplied when noticed. 
   In arranging the books on the shelves, the absolute location by shelf
 and book number is wholly abandoned, the relative location by class 
 and book number being one of the most valuable features of the plan. 
 The class number serves also as the location number, and the shelf num-
 ber in common use is entirely dispensed with. Accompanying the class 
 number is the book number, which prevents confusion of different books 
 on the same subject. Thus the first geometry catalogued is marked 
 513.1, the second 513.2, and so on to any extent, the last number show-
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