Although the purpose of this Handbook is to tell the principal facts about the Library as an institution, its chief use is likely to be that of a guide to the Central Building. The section about the Central Building is therefore given first place. Any visitor who cares to take the trouble, before beginning his tour of the Building, to read the brief historical sketch (on pages 63-73) will have a better understanding of the organization and work of the Library, and see the reasons for a number of things which might not otherwise be clear.