Aeolipile by Hero of Alexandria

The ancient invention of the steam engine by the Hero of Alexandria

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In our society today we are often surprised and impressed by the advancement of technology and engineering, a major characteristic of our civilisation. However if we look back more than 2,000 years ago, we can find mechanical marvels and incredible feats of engineering that were ahead of their time. Many became lost to the pages of history, only to become reinvented just a few centuries ago. This includes the first modern of the steam engine.

Heron of AlexandriaHeron Alexandrinus, or Hero of Alexandria as he was often known, was a Greek born in 10AD in Alexandria, now part of Egypt, and the second largest city after Cairo. Little is known about the life of Heron, however, we are aware that he was born to Greek parents that migrated to Alexandria after the conquest of Alexander the Great. Heron was a mathematician and an engineer considered to be one of the greatest inventors of ancient times.  

During the era in which Heron lived, the great Library of Alexandria was in its glory and Heron is believed to have taught at the Museum of Alexandria, a place for scientists and scholars to meet and discuss.

AeolipileWhat very few people know, thanks to the omission of important facts from our history books, is that Heron was the first inventor of the steam engine , a steam powered device that was called aeolipile or the ‘Heron engine’. The name comes from the greek word ‘Aiolos’ who was the Greek God of the winds.

Although a few others have talked about devices similar to aeolipiles before Heron, Heron was the first one to describe them in detail and give instructions for manufacturing them in his book Pneumatica, where more than 78 devices are described. Many of Heron’s ideas were extensions and improvements of another Greek inventor who lived in Alexandria 300 years before him, known as Ktesibios, the first to write about the science of compressed air.

But what is an aeolipile? It is a sphere that is positioned in such a way that it can rotate around its axis. Nozzles that are opposite to each other would expel steam and both of the nozzles would generate a combined thrust resulting in torque, causing the sphere to spin around its axis. The rotation force speeds up the sphere up to the point where the resistance from traction and air brings it to a stable rotation speed. The second video at the end of this article demonstrates how it works.

The steam was created by boiling water either inside the sphere or under it, as seen in the image. If the boiler is under the sphere, then it is connected to the rotating sphere through a pair of pipes that at the same time serve as pivots for the sphere. The replica of Heron’s machine could rotate at 1,500 rounds per minute with a very low pressure of 1.8 pounds per square inch.

PLACE a cauldron over a fire: a ball shall revolve on a pivot. A fire is lighted under a cauldron, A B, (fig. 50), containing water, and covered at the mouth by the lid C D; with this the bent tube E F G communicates, the extremity of the tube being fitted into a hollow ball, H K. Opposite to the extremity G place a pivot, L M, resting on the lid C D; 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 and across the lines F G, L M. As the cauldron gets hot it will be found that the steam, entering the ball through E F G, passes out through the bent tubes towards the lid, and causes the ball to revolve, as in the case of the dancing figures.
Heron, Pneumatica

This invention was forgotten and never used properly until 1577, when the steam engine was re-invented by the philosopher, astronomer and engineer, Taqu al-Din. But he basically described the same device as Heron, a method for rotating a spit by using jets streams on the periphery of a wheel.

Reconstruction of one of many “automata” of Heron ( Source)

Another invention of Heron was the ‘wind wheel’, a wind-driven wheel that was used to power a machine that was connected to a pipe organ.  He also invented the first vending machine, automatic opening doors, ‘ miraculous’ movements and sounds in temples, a fire engine, a standalone fountain, and many of the mechanisms of the Greek theatre. One of his theatrical mechanical inventions included a completely mechanical robotic theatrical play by using a binary system of knots and ropes and simple machines, even creating artificial sounds of thunder, pumps and concentration of light to specific parts of the performance. His works include descriptions of machines working on air, steam or water pressure, architectural devices for lifting heavy objects, methods of calculating surfaces and volumes – including a method of calculating the square root, war machines, and manipulation of light using reflection and mirrors.

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