“The seven tiers of stacks in which many of the books of the New York Public Library are shelved. Elevators transfer the books to the room above as they are called for.” From Scientific American..."
The image brings back pleasant memories of my undergraduate years, when I had a stack pass at some old libraries and used to wander the lower levels finding all sorts of unsought and unexpected items. (Not unlike browsing the Web now...)
Photo credit: NYPL Digital Gallery, via Make Bright the Sparrows.