block out the heat. Then over the years, Hay and a man named John Yellott constructed a 3- by 3.7-m building using water basins as the actual roofing material. During the summer, a slab of foam insulation was rolled back at night, and the water would become cold through the night sky evaporation. Since the water supply sat directly on a metal ceiling, it absorbed the heat from the room and kept the building air-conditioned all day. Durin
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