An aeolipile is a device consisting of an air-tight chamber (usually a sphere or cylinder) with bent or curved pipes projecting from it, through which steam is expelled in such a way as to create forces whose vectors are perpendicular to the radius of rotation, creating a net torque (or, informally, a rotational force). The resulting reaction torque causes the device to spin (Newton's third law). Typically, the water is heated in a basin, which is connected to the rotating chamber by a pair of pipes that also serve as the pivots for the chamber. However, the water may also be heated in the chamber itself as shown in the illustration below.

The aeolipile, invented in the first century by Hero of Alexandria, is considered to be the first recorded steam engine. Sadly, the device was thought of as nothing more than a diversion during Hero's lifetime, and the device hasn't received any serious recognition until relatively modern times. All Hero would have needed to do was capture this spinning energy and he would have created the steam engine... almost two thousand years before it was re-invented. Hero had other such contraptions to his name. Many of his inventions were for entertainment or religious purposes.

The name —derived from the Latin words "aeoli" and "pila"— translates to "the ball of Aeolus" ; Aeolus being the Greek god of the wind.

External links

• Building a replica of the aeolipile (includes a history of the aeolipile and an explanation of the principles behind it).
• Crude attempt at building a Hero's Engine with a soda can Cockeyed.com.