Humphrey,
Though I can't doubt your ingenuity in constructing this device, accounting for the weight of seven books of varying sizes, but I can't help but wonder at the practicality. Sure, it could be a more secure method of concealing a door behind a bookshelf, but I seriously doubt anybody would want to keep track of all of those books. Once we retrieve whatever it is you've locked in there, let's salvage what mechanisms we can and get a couple of the men to toss this thing into the water.
Signed,
High Artificer Bartholomew