=Definition.=—Classification consists of putting like things together. We do this every day, and the classification of books is only one special phase of this general process. Thus, a man who owns a hardware store does not place his goods helter skelter,—a stove, a box of nails, some saws and then a furnace, but he runs over his stock and classifies it, putting stoves in one place, nails in another. By this classification he gains two things: first, he can find any one thing he wants more quickly; secondly, he can tell how much of any one article he has on hand and so decide whether he must lay in a new supply. Likewise, the zoologist classifies all members of the animal kingdom, so that he can learn what the different kinds of animals are and study the relationship between them. Without the help afforded by classification he would be overwhelmed by the immense number of facts brought before him and without the aid of classification he would never have known of evolution, the guiding star of modern investigation. =First Principles.=—In our every-day life we lose much time hunting for things for which we have no definite place. We have put them in the place which was most convenient for us at the moment when we put them away. Think for yourself how it is with your knowledge. From observation, from conversation, from reading, you learn a little about many subjects like electricity, botany, astronomy or politics, but in this desultory way you do not learn very much about any one of these subjects. Therefore you do not feel any special need of classifying your information, but when you take up any of these subjects and pursue it seriously you learn thousands of facts and relations, and then is the time that you feel the need of some plan of arrangement of your knowledge. =Private vs. Institutional Libraries.=—One has the same experience in regard to books. A person having a library of from fifty to three hundred books does not feel the need of classifying them. The ordinary arrangement is based upon size, color or convenience. The books in the average house are so placed as to look their best. The classification, as far as it exists, is an esthetic one. The owner knows the exact appearance of every volume in his library and when he wants Longfellow’s poems he can tell at a glance where it is. In a small private library there is no occasion for all the history being in one place or all the poems in another. As the library grows, the esthetic principle of classification can be followed until the owner can no longer readily remember how each book looks.