Every such carrier should run from basement to top, with opening on every floor. A speaking tube should run beside it, with mouthpiece also on each floor.
Ledges. (See under Shelving, [p. 265].) As a ledge on both sides of each case would greatly narrow the aisles for passage and diminish the capacity for storage, these have disappeared from the modern stack. Their place has been taken in some stacks by sliding shelves (to be drawn out when wanted), which do not appear to be entirely satisfactory. But the need for some substitute, for the use of which Dewey speaks, has suggested ledges for folio shelving on each floor and for the new device of carrels, which may at least partially replace ledges without diminishing storage capacity or easy passage.
Shelves. The shelving of stacks follows the rules already described under the title “Shelving,” except as dimensions are varied by the use of steel, which is less bulky. Movable shelves also allow more variety in intervals to suit the average size of books in any part of the stack. It is usual to maintain the 10-inch height for intervals between shelves, all over the stack, except as thus modified here and there to suit exigencies and except for folio shelving at the ends (or sides) of each floor.
Different patents offer much choice in stack shelving. Avoid especially projections, likely to catch dust or tear clothing or injure books. Test very carefully all forms of “clutch” or detachable shelves.
Stack Lighting. Natural. North light is the best, but the choice is not often open. The location of the stack is determined usually by other considerations than aspect. Unless it runs along the rear or side of the main building; if it projects, that is, it will naturally have two sides lighted, one of which in any location would have to be south or west, and thus sunny. If wired glass is used as a protection against fire it will be more or less opaque and thus will temper glare. Shades can, of course, be used on the worst exposure, and some contrivance can be used, like that at the Library of Congress, to work all these curtains at once to save time.
Overhead light will penetrate one glass floor of a stack fairly well, not more.[297]
“If daylight is on the whole better and more wholesome, as it is certainly cheaper than electric light, then a well windowed stack room is better than a dark one.”—Russell Sturgis.[298]
Light penetrates stack aisles effectively only about twenty feet, hence a stack lighted on both sides may be forty feet wide, plus width of centre aisle.
Artificial. The best light is, of course, electricity, and here the expert of the stack to be installed can give valuable advice. The question of the location of the bulbs, their power, their direction (transverse or perpendicular), their frequency, their wiring, their switches, such questions must be determined. As a great deal might depend on the particular structure of the stack, one bid for the stack, another for the lighting, with specifications from each bidder, might be invited.