In the latest Age of Invention newsletter, Anton Howes picks up the story of the development of the steam engine (part one was linked here):

As I explained in Part I, the spark for my investigation was noticing that one Salomon de Caus, as early as 1615, had very probably made what amounts to a solar-powered version of Savery’s engine. By concentrating the sun’s rays on trapped air above the water in copper vessels, the resulting expansion of the trapped air and steam drove the water up a pipe to make a fountain flow. Most crucially of all, however, when the vessels cooled again they sucked water up and into them from a cistern below — a principle that de Caus also applied to having statues make music when the sun shone, and which he hinted may be useful for other things too.

Noticing this machine was a big shock to me, but de Caus’s invention was not even that original. It was actually an improvement of another, almost entirely ignored device described by Hero of Alexandria as early as the 1st Century, and which Hero in turn derived from one Philo of Byzantium who wrote in the 3rd Century BC.

Philo’s original device was very simple: a hollow leaden sphere with a bent tube rising out of it and into some water at the bottom of a jug. As the sun heated the sphere, the expanding air was pushed up the tube and into the jug’s water, escaping by bubbling out of the water. And crucially, when the sphere was removed from the sun and allowed to cool, the water was then drawn up the tube and into the sphere — Philo, about 1,900 years before Savery, had already encapsulated in a simple model the power of condensation to raise water.

Philo’s device was simple, but the principles it illustrated do appear to have been applied. Hero’s work, for example, includes a libas, or “dripper” fountain. In this alternative version of Philo’s apparatus, Hero connected the jug and sphere by two other pipes to a cistern underneath, as well as starting with some water already in the sphere. The jug now acted more like a funnel, into which the original bent tube now dripped its water like a fountain when the sun shone on the sphere. When cooled, however, the sphere replenished itself from the cistern underneath. It was almost exactly like de Caus’s version, which merely improved the strength of the fountain when it was heated, seemingly by replacing the lead with more heat-conductive copper and by using glass convex lenses to concentrate the sun’s rays.

Hero’s solar-powered dripping fountain doesn’t sound all that impressive, but both Philo and Hero appreciated the wider potential of its underlying principles.

Philo, for example, noted that it might make use of alternative heat sources: he described how his apparatus would work whether pouring hot water over the sphere, or by heating it over a fire. Once it cooled, it would always draw the water up.

Hero even suggested a mechanical use for the effect. By setting a fire on a hollow, airtight altar, the heated air within would flow down a tube into a sphere full of water, which in turn would be pushed up another tube into a hanging bucket. The bucket, when sufficiently heavy with water, would then pull on a rope to open some temple doors. Crucially, when the fire was extinguished, Hero noted that the cooling of the air in the altar would draw the water back into the sphere again, lighten the bucket, and so allow the doors to be closed by a counterweight. Although the condensing phase was really just for resetting the device, the fundamental ideas behind a Savery engine were already there: it raised water, used a fuel, and exploited condensation. It even did some light mechanical work.

In the latest Age of Invention newsletter, Anton Howes gives the first part of what promises to be a fascinating deep dive into steam engine development pre-dating the commonly accepted chronology of its invention:

What did I discover that so shocked me? When researching my last post on the inventors surrounding Prince Henry in the 1610s, and because I’ve been looking into the history of energy at the urging of Apoorv Sinha and others at Carbon Upcycling, I had a read through the published work of one of the inventors, Salomon de Caus.

De Caus often features in histories of the steam engine, as someone who in 1615 wrote about and depicted the expansive force of steam — heat up water in a copper vessel with a narrow tube coming out the top, and see how water or steam can be made to rise! He was even briefly known as the “true”, French inventor of the steam engine, because of a nineteenth-century hoax.

To historians of science and technology today, however, de Caus’s illustration is pretty unremarkable. He usually just gets a brief name-check, more or less copy-pasted from older histories. This is because the expansive force of steam would turn out not to be all that important in the development of the steam engine, as we’ll see, and because it was ancient.

3D animation of an aeolipile or Hero’s engine.
Animation by Michael Frey via Wikimedia Commons.

Hero of Alexandria, writing sometime in the first century, had already exploited the fact that when you boil the water in a metal vessel with a long, narrowing spout, the steam will come out with quite some force. This aeolipile, as it was sometimes called, was known and used throughout the middle ages and well into the seventeenth century. Sometimes it was shaped a bit like an alchemist’s retort, and known as the “philosophical bellows”. Other times, it was shaped as a human face, the steam issuing from its mouth — like the Greek god Aeolus, blowing the wind.

This was no mere toy, but found plenty of practical use. The spout of the philosophical bellows was often directed at a lamp’s flame, to have a sort of blow-torch effect. It was used, for example, to do finer tasks like bending glass pipes, or in fine metalwork — there are loads of accounts of this throughout the fifteenth, sixteenth, and seventeenth centuries, with some authors even talking about its merits relative to other instruments, suggesting real-life use. Its heat could, apparently, also be used to get fires going in wet weather, or from damp wood (provided you had some dry wood on hand to get the aeolipile itself going).

It could also be put to more sophisticated uses. Hero explained how the principle of thermal expansion — of either water or air — could be exploited to spout steam or even wine onto an altar’s fire to make it flare, to make water issue from a fountain, to make miniature dancers rotate and jump up and down, and to push air through bird-shaped automata to make them sing. A 1630s English version claimed to make the figure of a dragon hiss.

It could even be used to do some light mechanical work. Hero described a version that might make a hollow ball spin, by having the steam issue from bent nozzles. He even described a version where water could be forced by steam from one container into another, which would pull on a weight to open some doors. Taking his idea and running with it, engineers from at least the fifteenth century onwards wrote about directing the aeolipile’s narrow spout at miniature turbines to turn a roasting spits above a fire — suggested in Italy in Leonardo da Vinci’s notebooks, and in a 1551 Ottoman manuscript by Taqi ad-Din — or to do light industrial work like stamping ores and minerals into powders.

The principle of using heat to expand air or steam was even tried for much heavier-duty tasks. In 1605, the French inventor Marin Bourgeois developed an air-powered gun — known as the “wind-gun” — which used air that was pumped and compressed into the barrel. Within just a couple of years, having heard of the demonstration before the French court, and after paying a visit to Bourgeois, the mathematician David Rivault began experimenting on how the same effect might be achieved by heating water in a cannon. In the same decade, the Spanish military engineer Jerónimo de Ayanz y Beaumont also tried to use the expansionary force of steam to drive water up and out of mines — essentially, an industrial version of what Hero had done with fountains.