The Aeolipilewas the world's first rotating steam engine or more technically correct, a steam reaction turbine. It was devised by the great Heron of Alexandria in the 1st Century AD and described it in great detail in his book Pneumatica.
This relatively simple device works by heating a reservoir of water within the device to generating steam. The steam is then conducted through one of the copper supports to a pivoted brass sphere.
Once the steam reaches the sphere it escapes through one of two nozzles at the ends of two, small, opposingly pointing arms. The escaping steam generates thrust and causes the sphere to rotate.
The basic principle is simple but the device’s real genius is its bearings. Only one of the supported arms pass steam to the sphere (via a sleeve bearing).
This pushes the sphere against the other supporting ‘solid’ arm that also has a thrust bearing. The solid arm comprises of a conical point that bears against a matching indentation on the surface of the sphere. This combination holds the sphere in place whilst it rotates.