[Footnote 12: Note in illustration. Let us suppose a room 28 feet by 10, and a little over 9 feet high. Divide this longitudinally for a passage 4 feet wide. Let the passage project 12 to 18 inches at each end beyond the line of the wall. Let the passage ends be entirely given to either window or glass door. Twenty-four pairs of trams run across the room. On them are placed 56 bookcases, divided by the passage, reaching to the ceiling, each 3 feet broad, 12 inches deep, and separated from its neighbors by an interval of 2 inches, and set on small wheels, pulleys, or rollers, to work along the trams. Strong handles on the inner side of each bookcase to draw it out into the passage. Each of these bookcases would hold 500 octavos; and a room of 28 feet by 10 would receive 25,000 volumes. A room of 40 feet by 20 (no great size) would receive 60,000, It would, of course, be not properly a room, but a warehouse.]