(If the public is excluded, three feet is ample.) No shelf, in any form of bookcase, should be higher than a person of moderate height can reach without a stepladder.
Shelving for folios and quartos should be provided in every book room.
Straight flights are preferable to circular stairs.
The form of shelving which is growing in favor is the arrangement of floor cases in large rooms with space between the tops of the bookcases and the ceiling for circulation of air and the diffusion of light.
Modern library plans provide accommodations for readers near the books they want to use whatever system of shelving is adopted.
Single shelves should not be more than three feet long, on account of the tendency to sag.

Ten inches between shelves, and a depth of eight inches, are good dimensions for ordinary cases.

Shelves should be made movable and easily adjustable.

Many devices are now in the market for this purpose, several of which are good." Don't cut up your library with partitions unless you are sure they are absolutely necessary.

Leave everything as open as possible.