Sashes for openings in glazed roof

2081. Movable roofs are either composed of sashes 6 ft. or 8 ft. long, and 3 ft. or 4 ft. wide, which slide over each other and are moved by cords and pulleys; or they are formed of sashes which open outwards at their lower extremety, and have hinges at the upper part. Sometimes the lower sashes are made movable, while the upper part of the roof is fixed, as in the case of domes, or acuminated roofs, the upper part of which rises in the manner of a skylight.