maximum width should not exceed 30 feet, and only be that if the room is lofty and the windows high up. The colour of the walls is an important factor, as dark colours absorb much of the light, while light colours reflect and diffuse the rays of light which fall upon them. A dado of glazed bricks or tiles around reading-rooms is of value, both from a sanitary point of view as well as that of helping to diffuse the light.
So far, we have considered the lighting of rooms by side lights only. A top light can be obtained in some of the rooms of most buildings, and its use is often advantageous. The readers can be arranged without regard to shadows, as all parts of the room are equally well lighted, and there is no limit to the size and shape of the rooms. The inconveniences of top lights are, the difficulty of keeping them rain-proof, and the draughts which are caused by the heated air ascending, chilling against the cold glass, and falling back again in cold currents. The first defect can be minimised by inserting clear glass windows in the clerestory only, and not in the slope of the lantern. The second can be met by an inner glass ceiling, which also has the advantage of intercepting the direct rays of the sun, and so keeping the room at a low temperature during the summer months. In the Edward Pease Public Library, Darlington, the roof of the reading-room is ceiled in this manner, with lightly-coloured stained glass. Each square is lifted about two inches from its bed by supports at the corners, and so allows free egress for the vitiated
