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Door opening device. Diagram of a device designed by Hero of Alexandria (flourished 1st century AD) to open temple doors. As the fire on the altar (at upper left) heated the air beneath it, the gas expands and forces its way into the sphere (at bottom left). The sphere contains water which is forced out by the gas into the bucket. When enough water has flowed into the bucket, its weight will overcome that of the weight (at bottom right) holding the doors closed. The bucket will descend, pulling on ropes which are wound around poles that are attached to the doors and so open them. Intricate devices like this were popular in Hero's time. Image taken from Hero's Pneumatics.
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