=How to use the Handbook.=--The one fixed point in the arrangement of the National Gallery is the numbering of the pictures. The numbers affixed to the frames, and referred to in the Official Reports and Catalogues, are never changed. This is an excellent rule, the observance of which, in the case of some foreign galleries, would have saved no little inconvenience to students and visitors. In the present, as in the preceding editions of the Handbook, advantage has been taken of this fixed system of numbering; and in the pages devoted to the Biographical and Descriptive Catalogue the pictures are enumerated in their numerical order. The introductory remarks on the chief Schools of Painting represented in the Gallery are brought together at the beginning of the book. The visitor who desires to make an historical study of the Collection may, if he will, glance first at the general introduction given to the pictures in each School; and then, as he makes his survey of the rooms devoted to the several Schools, note the numbers on the frames, and refer to the Numerical Catalogue following the series of introductions. On the other hand, the visitor who does not care to use the Handbook in this way has only to skip the preliminary chapters, and to pass at once, as he finds himself before this picture or that, to the Numerical Catalogue. For the convenience, again, of visitors or students desiring to find the works of some particular painter, the full and detailed Index of Painters, first introduced in the Third Edition, has here been retained. References to all the pictures by each painter, and to the page where some account of his life and work is given, will be found in this Index. Finally, a concise Numerical Index is given, wherein the reader may find at once the particulars of acquisition, the _provenance_, and other circumstances regarding every picture (by a foreign artist) in the possession of the National Gallery, wherever deposited.