aeolipile

aeolipile, steam turbine invented in the 1st century ce by Heron of Alexandria and described in his Pneumatica. The aeolipile was a hollow sphere mounted so that it could turn on a pair of hollow tubes that provided steam to the sphere from a cauldron. High-pressure steam escaping from the sphere was sent through bent tubes, causing the sphere to spin.

Like many other machines of the time that demonstrated basic mechanical principles, it was simply regarded as a curiosity or a toy and was not used for any practical purpose. Centuries later, however, it was adapted as a fire-blowing tool and possibly as a rudimentary power-generating machine. The aeolipile is the first known device to transform steam into rotary motion (see also steam engine).

Operation and purpose

To operate, the cauldron beneath the aeolipile was first filled with water, and a fire under the base of the cauldron heated the water to a boil. Steam generated in the cauldron would travel upward through pipes into a hollow sphere, where pressure would build up and push the steam through narrow outlets on the ends of two or more bent hollow tubes positioned along the sphere’s equator. The outlets were oriented in the same direction (either clockwise or counterclockwise), which allowed the expelled steam to drive the sphere’s rapid rotation.

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The purpose of Heron’s aeolipile remains a matter of conjecture. A number of sources note that the device was used as a simple toy that helped Heron demonstrate his understanding of physics to impress other thinkers of the time. Others speculate, however, that the aeolipile could have been used along with Heron’s other inventions—he was known as Mechanikos (“machine man”) and was highly regarded at the time—to perform seemingly miraculous feats before visitors to Roman temples.

Legacy

Although the aeolipile was not used as a tool or a power source in antiquity, it became the basis of practical innovations centuries later. Some records note that during the 10th century in France the aeolipile was adapted to create sounds in a hydraulic organ. By the 17th century it inspired the development of air-blowing tools that sent focused jets of steam at turbines to turn roasting spits or to blow over coals to increase the heat of a fire used to melt glass and metal.

The first use of an aeolipile as a source of power may have occurred during the 16th century, after Spanish scientist and naval officer Blasco de Garay presented his idea for an engine that could propel sailing ships to Holy Roman emperor Charles V in 1543. According to a letter written by the director of the royal archives of Simancas, Charles V ordered a sea trial, and de Garay constructed a modified aeolipile to power wheels attached to opposite sides of a ship. Although the wheels were said to have driven the vessel forward at about one league (5.6 km) per hour through the water, the apparatus was viewed as too expensive, complicated, and dangerous to be practical, and de Garay abandoned the project.