In the "Advancement of Learning" Bacon refers to the annotations of books as being deficient. There was living at the end of the sixteenth and beginning of the seventeenth century a scholar through whose hands at least several thousand books passed. He appears to have made a practice of annotating in the margins every book he read. The chief purpose, however, of the notes, apparently, was to aid the memory, for in some books nearly every name occurring in the text is carried into the margin without comment. The notes are also accompanied by scrolls, marks, and brackets, which support the contention that they are the work of one man. The annotation of books was not a common practice then, nor has it been since. If a reader takes up a hundred books in a second-hand book shop he will probably not find more than one containing manuscript notes, and not one in five hundred in which the annotations have been systematically carried through. There does not appear to have been any other scholar living at that time, with the exception of this one, who was persistently making marginal notes on the books he read. Spedding writes: "What became of his (Bacon's) books, which were left to Sir John Constable and must have contained traces of his reading, we do not know; but very few appear to have survived." Mrs. Pott, in "Francis Bacon and his Secret Society," draws attention to the mystery as to the disappearance of Bacon's library. "Which is a mystery," she adds, "although the world has been content to take it very apathetically. Where is Bacon's library? Undoubtedly the books exist and are traceable. We should expect them to be recognisable by marginal notes; yet those notes, whether in pencil or in ink, may have been effaced. If annotated, Bacon and his friends would not wish his books to attract public attention." And further on: "It is probable that the latter (_i.e._, the books) will seldom or never be found to bear his name or signature." And again: "Yet it may reasonably be anticipated that some at least are 'noted in the margin,' or that some will be found with traces of marks which were guides to the transcriber or amanuensis as to the portions which were to be copied for future use in Bacon's collections or book of commonplaces." Mrs. Pott's words were written in a spirit of true prophecy.