The process is necessarily quite expensive, because of the time required and of the small number of competing artists in this field. It is chiefly confined to the restoration of imperfect copies of early printed and rare books, which are so frequently found in imperfect condition, often wanting title-pages or the final leaves, or parts of pages in any part of the volume. So costly, indeed, is this skilful hand-restoration of imperfect books, that it has been a great boon to the collectors of libraries and rare works, to see the arts of photography so developed in recent years, as to reproduce with almost exact fidelity printed matter of any kind from the pages of books. The cost of such facsimiles of course varies with the locality, the work, the skill, or the competition involved. But it may be said in general that the average cost of book-page facsimiles by photographic process need not exceed one dollar a page. An entire edition of the Encyclopaedia Britannica has been printed from plates made in replica from photographs of the original text of the Edinburgh edition. The reproduction in this case can hardly be commended, as it is trying to the eyes to read, when compared with the original, presenting a somewhat blurred and irregular aspect to the eyes. It is very difficult to lay down rules which shall be effective in checking the abuse of books which compels exercise of the means of restoration. Writing upon margins (already referred to) may sometimes be checked by putting a printed slip in every library book bearing the warning--"Never write in a library book." To this may be added--"Never turn down leaves," an equally important injunction. Indeed, a whole list of "Dont's" might be inserted, but for the chance that too many warnings might operate to warn off a reader from absorbing any of them. Thus-- "Don't soil any book Don't write on margins Don't turn down leaves Don't lay a book on its face open Don't wet fingers to turn leaves Don't fail to use the book-mark Don't read with unclean hands." As a loose slip is liable to fall out, some such reminder should be pasted into the fly-leaf of every book, next the book-plate.