obvious defects, this indexing apparatus must be considered the mother, if not grandmother, of all the various methods invented to circumvent the permutations of the alphabet, The book, guarded or otherwise, in which a Page or leaf containing several entries forms the unit for arrangement, is really the first of the five groups into which the various existing methods naturally divide themselves. I need only mention the public catalogue of the British Museum as a type of this group. The second group comprises most of the Card systems, in which, as a rule, a single entry is the unit for arrangement, though I shall show you forms which admit of a different treatment. The third group I prefer to name the Sheaf system, from the fact that entries on slips are collected or bound up in bundles. In this system, the whole of an author's works can be made to form the unit for arrangement. The fourth group may be called the Broadside or Placard system, from the circumstance that a series of entries or single movable titles are arranged in frames of various kinds. In this the column of entries is the unit for arrangement; and it, therefore, closely resembles in principle the "Page" systems of the first group, though differing from them in the method of display. The fifth and last group may be called the Panoramic system for want of a better name: and in this the unit for arrangement is the single entry applied to a continuous column of limited capacity. Mr. Mason's revolving drum may be mentioned as one type of this group. I have now set forth the five heads under which I propose to describe some of the cataloguing methods in existence; and, I trust, if the difficulty of the subject excludes the hope of making it amusing, your professional interest will, at least, move you to follow me with a decent show of patience. There are probably twenty or more " Page " systems in use, including those with fixed and movable leaves, besides two methods in which the single entries are also movable, as well as the leaves.
I shall only mention two of the fixed "Page" systems, because they are representative of all the rest. One is the catalogue of the British Museum, in which the alphabet of entries is distributed over a large number of volumes, thereby rendering one copy of the catalogue of service to very many readers. The other is the Mitchell Library Catalogue, in which an entire alphabet fills one volume, thus making necessary the provision of many complete catalogues before an adequate number of readers can consult it at one time. There are several
