In a private library, where the service of books is commonly to be performed by the person desiring to use them, they ought to be assorted and distributed according to subject. The case may be altogether different where they have to be sent for and brought by an attendant. It is an immense advantage to bring the eye in aid of the mind; to see within a limited compass all the works that are accessible, in a given library, on a given subject; and to have the power of dealing with them collectively at a given spot, instead of hunting them up through an entire accumulation. It must be admitted, however, that distribution by subjects ought in some degree to be controlled by sizes. If everything on a given subject, from folio down to 32mo, is to be brought locally together, there will be an immense waste of space in the attempt to lodge objects of such different sizes in one and the same bookcase. And this waste of space will cripple us in the most serious manner, as will be seen with regard to the conditions of economy and of accessibility. The three conditions are in truth all connected together, but especially the two last named. Even in a paper such as this the question of classification cannot altogether be overlooked; but it is one more easy to open than to close--one upon which I am not bold enough to hope for uniformity of opinion and of practice. I set aside on the one hand the case of great public libraries, which I leave to the experts of those establishments. And, at the other end of the scale, in small private libraries the matter becomes easy or even insignificant. In libraries of the medium scale, not too vast for some amount of personal survey, some would multiply subdivision, and some restrain it. An acute friend asks me under what and how many general headings subjects should be classified in a library intended for practical use and reading, and boldly answers by suggesting five classes only: (1) science, (2) speculation, (3) art, (4) history, and (5) miscellaneous and periodical literature. But this seemingly simple division at once raises questions both of practical and of theoretic difficulty. As to the last, periodical literature is fast attaining to such magnitude, that it may require a classification of its own, and that the enumeration which indexes supply, useful as it is, will not suffice. And I fear it is the destiny of periodicals as such to carry down with them a large proportion of what, in the phraseology of railways, would be called dead weight, as compared with live weight. The limits of speculation would be most difficult to draw. The diversities included under science would be so vast as at once to make sub-classification a necessity. The ologies are by no means well suited to rub shoulders together; and sciences must include arts, which are but country cousins to them, or a new compartment must be established for their accommodation. Once more, how to cope with the everlasting