The reason that books cannot be as closely classified as magazine articles is that they generally deal with broader topics. In the average library it does not pay to classify books more minutely than is warranted by the general run of books in the class in which these books are to be assigned. In this regard, a distinction must be made between libraries. The Library of Congress has devised a classification of its own which is very minute, and a number of classifiers are employed to look after the different fields in which they are more or less expert. In this way, classification can be carried to the extreme limit of closeness. Nothing keeps one more modest than classifying, for one is continually brought face to face with things that one does not know, and so many things of which one knows so little. =The Dewey Decimal Classification.= The decimal classification is used in this country and in Europe. It is suitable for both large and small collections of books and for indexing. In many schemes of classification letters are used to denote the classes, in others a combination of letters and figures. Dewey uses only figures. Dewey developed his system in 1873 and published it in 1876. Numbers of three figures were used to denote the classes. Since then it has been found desirable to subdivide much more minutely and this has been done with increasing minuteness in the seven editions that have followed the one of 1876. A general outline of Dewey is here given. 000 General works 100 Philosophy 200 Religion 300 Sociology 400 Philology 500 Science 600 Useful arts 700 Fine arts 800 Literature 900 History Each of these is divided into ten sections, e. g. 500 Science 510 Mathematics 520 Astronomy 530 Physics 540 Chemistry 550 Geology 560 Paleontology 570 Biology 580 Botany 590 Zoology Each of these is divided into ten sections, e. g. 530 Physics 531 Mechanics 532 Hydraulics 533 Pneumatics 534 Sound 535 Light 536 Heat 537 Electricity 538 Magnetism 539 Molecular physics.