591,985. Buildings; roofs; ventilation. STEVENS, H. H. Dec. 9, 1943, No. 20591. Convention date, Nov. 26, 1942. [Classes 20 (i), 20 (iv) and 137] [Also in Group XIII ] Relates to buildings having a flexible roof supported by air pressure. According to the invention, a membrane of substantially gas-impermeable material, unrestrained by any confining network or ropes or system of stiffening rods &c., serves as the roof of a building, the periphery of the roof being anchored to a fixed support, and the roof being supported in a raised, domed condition by air pressure within the building. The impermeable membrane is preferably made of ductile material such as strips of annealed low carbon steel welded together at their longitudinal edges, but other materials such as aluminium, vulcanized fibre, laminated paper board, or plastics, e.g. cellulose acetate, may be used. The building may be a large structure, advantageously circular (a diameter of 1,200 feet and a height of 60 feet are mentioned as practicable), and it may serve for many purposes such as that of a factory or as a housing for vehicles, aeroplanes, &c. Such a building may be applied for enclosed shipyards, docks for submarines &c. by constructing it to extend over water, with the peripheral support for the roof located below the water. Further applications described are the generation of power by utilizing the heating by solar rays and otherwise of the air within the building, and also the use of the building for horticulture. Fig. 1 shows a vertical section of the building and Fig. 4 shows the floor in plan. The peripheral edges of the roof 50 are welded to an anchoring bar or the like which is secured to a low surrounding wall 51 of concrete. Various other means for securing the roof to the wall, including additional anchorage to the ground, are described, e.g. the said anchoring bar &c. may be welded to wire or perforated sheets embedded in the concrete. Several forms of peripheral walls are also described. The wall may be moulded in trenches, and may be shored. To support the roof in domed condition, air at a pressure somewhat above atmospheric is supplied to the chamber formed by the membrane, the surrounding support, and the floor. The air pressure creates within the membrane tensile stresses in all directions. The air is preferably supplied by means of air blowers arranged externally at 73, 74 round the periphery. The blowers, which may be arranged in pairs, to work at relatively high or low pressure, supply air through ducts 55 which pass under the supporting wall and which lead to concentric distributing ducts 57; these discharge the air through outlets 58 in the floor, at which outlets regulating baffles may be provided. Towers 59 are erected within the chamber, to allow air to pass out at places where the temperature is relatively high, the towers communicating with exit ducts 60 which may be located between the inlet ducts 55. The outgoing air may drive air turbine motors 84, Fig. 5, to assist electric or other motors 79 to drive the blowers 56. Incoming air may be warmed by the exhaust air, or may be otherwise conditioned. Entry to and exit from the building may be effected through revolving doors or equivalent means, or by a set of doors constructed as an air lock. The impermeable roof membrane may be covered with protective material such as insulating board and asphalt, and may have inside a light and heat reflecting surface, or may be suitably coated, e.g. with aluminium, for this purpose. Means for heatinsulation and sound-proofing may also be provided, as in the composite roofing material shown in Fig. 19. This comprises an impermeable " primary " membrane 61, having above it insulating material 86 and an asphalt or like roofing surface 87, while below are a layer 88 of flock or other soundabsorbing material and a metallic reflecting surface 85. When the structure is intended to serve as a means for generating power from the sun's rays, the primary membrane embodied in the roof is transferred to solar radiation within a suitable range of wavelengths, but opaque to heat radiation. of longer wave-lengths, and the heat-insulating property of the ray is preferably increased by the formation of air spaces therein. Energy is thus derived by the heating of the air in the chamber and its consequent discharge at a temperature and pressure greater than that of the incoming air. Advantage may also be taken of atmospheric changes of temperature and pressure, by selecting the times at which air is admitted to and discharged from the chamber, and the waste heat from lights, machinery &c. when the building is used as a factory is said to be also utilizable. Solar heating boilers may be used as auxiliary means for deriving energy from the sun's rays, and it is stated that the low temperature heat wasted in the operation of such boilers, or in the cultivation of vegetation within the enclosure, may be utilized by the invention.