Hero of Alexandria (AD 10–85) was a brilliant teacher of mathematics and physics at the Musaeum (which encompassed the famous Library of Alexandria). He shared Archimedes’ knack of converting his academic genius into the creation of remarkable devices. His inventions included the world’s first vending machine, which provided a measure of holy water in return for a bronze five-drachma coin; a wind-powered organ; the force pump; and a famous stand-alone fountain that was named after him.
He also created a set of self-opening doors that were used by temple priests to create a sense of wonder. When a fire was lit, the water in a concealed metal globe heated up. It was then forced through a tube into a bucket, whose weight pulled the doors open via a system of pulleys. When the fire was extinguished, the water in the system cooled and was sucked back into the globe, whereupon the bucket rose and the doors closed themselves.
A number of these inventions relied on the transference of weight or the use of water within an enclosed system. The vending machine worked because the weight of the coin pulled a small pan downwards and opened a valve, which allowed the holy water to escape. Hero’s stand-alone fountain was powered by hydrostatic energy (the buoyancy factor that makes objects feel lighter in water), and the temple doors worked because of the expansion and evaporation of heated water. Hero’s most famous invention – the aeolipile – used some of these elements in a novel way to create a device that can reasonably be described as the world’s first steam engine (and which also prefigured the jet engine).
The aeoliopile is considered to be the first recorded steam engine.
The aeolipile consisted of a closed cauldron containing water, which was heated by a fire. As the water heated up, the steam rose through two pipes that acted as the axle for a globe mounted between them. The globe had two outlets, through which the steam could escape. The escaping steam forced the globe to rotate rapidly on its axle. (One recent recreation of the aeolipile rotated at an astonishing rate of 1,500 rpm, which is impressive even when compared with modern steam turbines.)
Hero’s engine, as it is commonly known, was not a practical device for generating energy as it was simply too inefficient – it was created more as a mechanical marvel than for the purpose of industry. However, the same technology could in theory have been combined with cylinders and pistons (which Hero utilized in other devices, such as his firefighting water pump) to create a more viable energy source. It is unclear why Hero didn’t take this next step. Some have speculated that, given the widespread slavery and the ongoing threat of warfare in this period, inventors tended to look for impressive illusions, recreational devices or military applications, rather than seeking to replace the ready supply of slave labour.
To understand how remarkable Hero’s achievement was, we need to bear in mind that true steam power wasn’t developed until the seventeenth century. Jerónimo de Ayanz y Beaumont patented a basic steam-powered water pump in 1606; Thomas Savery’s 1698 steam pump used condensing steam to pressurize steam to pump water; the atmospheric engine of Thomas Newcomen, which came into use in 1712, powered pumps for the mining industry; and it wasn’t until 1781 that James Watt invented the first steam engine which could power continuous motion. So Hero richly deserved the accolade of his nickname Michanikos, the Greek word for ‘Engineer’.