this effect is minimized. In mild climates the ceiling light is sometimes omitted entirely but the attic space between the outer skylight and an inner glass ceiling is valuable in many ways, especially for ventilation. Excessive summer heat and winter cold are kept confined in the loft above the glass. A warning is necessary here in regard to the space above the ceiling light. It is one of the most important things in the whole museum that this should be accessible, decently finished and large enough to be ventilated and cleaned. The janitor should be able frequently to clean the ceiling lights, the electricians to work comfortably on the wires provided for artificial illumination which is now always above the ceiling light, and the beams and girders should be so placed that it is possible to provide curtains or shades or louvres to exclude too abundant light. Where the loft between the two glasses is small, the heat accumulates in this space in summer and it requires a very efficient system of ventilation to take care of it, but where the loft is large enough, it is easy to arrange openings provided with louvre vents in opposite walls so that a direct draft can be obtained. The dust that enters in this way is a serious matter but the heat in the galleries is worse, and, as the glass of the ceiling lights is usually set with felt, the dust that seeps through
