I finished reading the trilogy of His Dark Materials, and am now reading about how one man tried to unearth every copy (both first and second editions) of Copernicus' "De revolutionibus" (in which Copernicus first suggested that the Sun was the centre of the universe rather than the earth).

I'm impressed by the diligence in which the author would read the comments scribbled in margins by past owners of the books, and from there deduce if the book was just a bookshelf showpiece, or used as a tool of understanding. Not only that, in some cases, he would track the copies from their source to final resting place too.

It's like Bookcrossing of the past.