My condolences also to Steven on his sad loss
Third replying to Drykid, I had a look at the book today as it is some years since I had seen it. It has been severely damaged by damp at some stage and the pages have been mounted on card to save further deterioration. It starts with some accounts from 1816 on the first five pages. Then pages six to 43 were blank when NB bought it and the bulk of the diary is on these. Pages 44 onwards have further accounts from 1797. There was some room on pages 44 & 45 and NB wrote entries on these. Clearly NB bought it second hand as it dates to before his birth! As you can see from the picture of Steven it is in large format, somewhat bigger than A4. A book like this would have been quite expensive new as paper was still largely hand made I believe.
OK thanks for that; it confirms pretty much everything I suspected; it also confirms why the diary ends early on Dec 12th, since he clearly filled all available space and needed to start the next volume early. I wonder if he added the remaining entries to his 1847 diary or just stopped journaling altogether until the start of the next year.
I'm also curious at what point the water damage occurred; whether it was before the 1846 one got separated from the others or not. Although I guess I'd just be grateful for the missing ones to turn up, water damage or not. It does offer a potential explanation for the non-survival of the others though; if they were all exposed to substantial flooding at some point then it's possible that only this one was considered to be in a state worthy of keeping afterwards (maybe because of its binding), and the others were binned. Though I hope I'm wrong.
A bit of light reading for later on then ... 
Hah well I may have read on a bit, purely out of curiosity you understand. I did learn a new word from the same story: the verb "to gamahuche", which I couldn't possibly elaborate on here. Suffice to say that if Nat ever uses it re: Ann Fox, then it means things have moved on considerably between them...
