Hero's aeolipile and steam boiler, 1st century BC.
© Science Museum / Science & Society Picture Library
This working model is based on sketches from 16th century manuscripts. Hero, or Heron, of Alexandria was a Greek mathematician. He described the aeolipile in his treatise on pneumatics (the study of the mechanical properties of gases) in c 100 BC. It consists of a hollow ball mounted on its axis between two pivots, one of which serves as a steam pipe from the cauldron below, supporting the whole. The ball is provided with two bent nozzles in a plane at right angles to the line joining the pivots. The escape of jets of high presure steam causes the ball to rotate. Hero considered the aeolipile to be little more than a toy, but it could be regarded as an elementary form of steam turbine.