My Gravity Falls theory about the books!
I believe this screenshot from the preview is a flashback. Remember when Dipper found his book in the ground? This is the exact same background (Tree on ground etc) only at night. When Dipper found the book, it was a lock you could open with a machine. This person burries the book so this must be before he/she made the device.
And what character in this show is known for making machines?
I believe this person may be Old Man Mcgucket.
I doubt if he actually wrote the book.
In another screenshot you see book 1. Or book 0 because there isnt a number on it. If you look close, you see this book is about machines and stuff like that.
This is a different book than the one Dipper found, so the person burrying the book isnt the same person as reading the book.
I think Old Man Mcgucket got a hand on the first book and got pretty good at making machines and stuff. But, he lost the book. (Maybe he hid it too well?) Now he tries to make machines from what he can remember from the book.
He went crazy trying to remember.