The task of describing and illustrating any delicate and complicated manual process in popular articles has several distinct difficulties. The audience is necessarily mixed. If anything is assumed as known, those who do not know it are at a disadvantage. If nothing is assumed, the articles expand into a full manual of the process. Also, as in practice, the acquirement of one process overlaps another, so, in treating of processes, it is very difficult to divide them sharply. No subject or process in book-binding is ever really finished in the sense of being put out of the way. Every ill-done process rises up to accuse and harass all through the work.