I have just found out something very interesting about the way big libraries (and small ones too, I imagine) work. This was the result of a meeting with an extremely kind and helpful lady who is a librarian (among other roles) here in Cambridge. You might think that the catalogues that are published, put on the web or placed on card indexes in the reading rooms are the sum total of the information available on the contents of libraries. Not a bit of it. There are lots of lists that librarians over the years have made which might be of help for particular research if only you could get your hands on them. One at Cambridge is the list of books containing the signature of the Cambridge magician, John Dee (he had a lot!). I'm interested in annotations made to science and maths books by certain owners. The technical term for an annotated book is adversaria or ADV for short and these are often catalogued separately. My next task is to go through the Cambridge lists and see if they include annotations by anyone I am interested in. A lot of work - but better than having to check all the books individually!