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Public Libraries in the United States. 
the directions for using the subject catalogue; and the condensed rules 
for the headings and titles of the cards. 
  The library is first divided into nine special libraries, which are called
classes. These classes are (1) Philosophy, (2) Theology, (3) Sociology, 
(4) Philology, (5) Natural Science, (6) Useful Arts, (7) Fine Arts, (8) 
Literature, and (9) History, and are numbered with the nine digits; 
thus Class 9 is the Library of History, etc. These special libraries or 
classes are then considered independently, and each one is separated 
again into nine special divisions of the main subject. These divisions are
numbered from 1 to 9, as were the classes. Thus 59 is the ninth division
(Zoijlogy) of the fifth class, (Natural Science.) A final division is then
made by separating each of these divisions into nine sections, which are
numbered in the same way with the nine digits. Thus 513 is the third 
section (Geometry) of the first division (Mathematics) of the fifth class,
(Natural Science.) This number, giving class, division, and section, is 
called the classification or class number, and is applied to every book or
pamphlet belonging to the library. All the geometries are thus num. 
bered 513; all the mineralogies 549; and so throughout the library, all 
the books on any given subject bear the number of that subject in the 
scheme. Where a 0 occurs in a class number it has its normal zero 
power. Thus, a book numbered 510 is Class 5, Division 1, but no sec- 
tion. This signifies that the book treats of the Division 51 (Mathemat. 
ics) in general, and is not limited to any one section, as is the geometry,
marked 513. If marked 500, it would indicate a treatise on science in 
general, limited to no division. A zero occurring in the first place 
would in the same way show that the book is limited to no class. Tile 
classification is mainly made by subjects or content regardless of form;
but it is found practically usefLl to make an additional distinction in 
these general treatises, according to the formn of treatment adopted. 
Thus, in Science we have a large numb)er of books treating of science in
general, and so having a 0 for the division number. These books are 
then divided into sections, as are those of the other classes, according
to the form they have taken on. We have (1) the philosophy and history 
of science, (2) scientific coml)ends, (3) dictionaries, (4) essays, (5) periodi-
cals, (6) societies, (7) education, an d (8) travels - all having the common
subject, Natural Science, but treating it in these varied forms. These 
form distinctions are introduced here because the number of general 
works is largc, and the numerals allowv of this division without extra 
labor, for the numbers from 591. to 509 would otherwise be unused. 
They apply only to the general treatises, which, without them, would 
have a class number ending with two zeros. A dictionary of mathe- 
matics is 510, not 503, for every book is assigned to the most specific 
head that will contain it, so that 503 is limited to dictionaries or cyclo-
1)edias of science in general. In the sa'ne way a general cyclopmetlia or
periodical treats of no one class, and so is assigned to the Class 0, 
divided into cyclop&edias, periodicals, etc. No difficulty is found in
fol-