Hero of Alexandria was not the first ancient scientist to toy with steam driven devices. According to Leonardo da Vinci, the fourth-century Greek scientist Archimedes invented one of the first steam driven devices in 330BC. The invention was a steam-powered cannon, fueled by water heated over coals. According to Da Vinci, the device could hurl 70-pound iron balls at the enemy. Archimedes was later followed by Hero’s ‘hero’, Ctesibius who in 250BC invented a water-filled metal sphere that rotated when heated or placed in water. It could be Ctesibius’s device formed the inspiration behind Hero’s aeolipile.
Hero named his steam-powered machine after Aeolus, the Greek god of wind. His description of the device and how to use it was relatively brief. “ Place a cauldron over a fire: a ball shall revolve on a pivot, ”began the brief passage in his Pneumatics. The aeolipile’s operator was then instructed to light a fire“ under a cauldron containing water and covered at the mouth by the lid; with this, the bent tube communicates, the extremity of the tube being fitted into a hollow ball.
The description of the aeolipile’s design and use continues as follows: “Opposite to the extremity place a pivot resting on the lid and let the ball contain two bent pipes, communicating with it at the opposite extremities of a diameter and bent in opposite directions, the bends being at right angles. As the cauldron gets hot, it will be found that the steam entering the ball passes out through the bent tubes towards the lid and causes the ball to revolve.”
Although Hero’s contemporary, Vitruvius also refers to the aeolipile, Hero’s description and explanation of the device’s workings is the first detailed account of this particular form of machine. For although Archimedes may have pioneered the use of steam in propulsion and Ctesibius the application of heat to cause rotation, Hero’s device was the first to combine the two principles to use steam to drive a rotor. In effect, Hero of Alexandria had devised an early form of the steam engine- sixteen centuries before society recognised its invention.