comparison of the copies must be made, that the best bound and best conditioned copies may be kept, and, especially in the case of the older books, that the library may not lose a duplicate containing MS. notes or corrections. (The British Museum, it may at this date be freely admitted, disposed of several treasures in its duplicate sales in times long past, and sometimes had to buy them back again at enhanced prices. One book at least had been in a royal collection, and contained notes in a royal hand.) Two copies of a book printed in the first ten or twenty years after Gutenberg may always be kept with advantage, since a close examination will often reveal that what appears to be duplicate copies really belong to different editions, parts having been corrected, or even reprinted, in a way that often throws light on the history of printing.
The rules for " weeding-out " of books from libraries of the second rank depend on the size and aims of these collections. If space allows, the first edition of a book of literary or scientific interest should not be parted with. Intermediate editions may generally be spared. Peerages and other similar publications, that are periodically reprinted with corrections and additions, must be weeded out warily. Thus Minerva and the Annuaire de la Noblesse are not complete in any single issue, but constantly refer the searcher back to an earlier edition for the information he needs. Each new issue of " Men of the Time " or Burke's " Peerage " omits certain notices contained in the previous
