As regular readers might have noticed, it’s been a long time since my last newsletter — far, far longer than usual. Although I haven’t been posting, however, I have been hard at work researching. I had to translate a lot of primary sources from sixteenth-century French, Italian, Dutch, German, and even Latin, so that was already going to cause a delay. But then, the more I delved into the topic, the more I had to delay writing it up. Things I thought I knew, and on which I agreed with a lot of other historians, turned out to be ever more questionable. Perhaps even wrong. And so I had to delve ever deeper to get to the truth, and to reformulate what I knew.

So I apologise for the delay. But I hope this post will be worth the extra wait. 

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.¹

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.

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).²

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.

And then there was the power of the flue. Small turbines were already being applied to chimneys from as early as the fifteenth century, whereby the rising air drove roasting spits. And possibly more. One English writer in the late 1640s, reporting on an Italian version he’d read about from almost a hundred years earlier, noted how the same device could also be used “for the chiming of bells or other musical devices”, “for the reeling of yarn, the rocking of a cradle, with diverse the like domestic occasions.” He fully understood how it worked, noting that even when there wasn’t an actual fire in the hearth, that if the air outside was colder than within the room then the warm air would rise through the flue to drive the mechanism “as experience shows”. Even earlier, in 1620s Rome, Giovanni Branca depicted a flue-powered slitting mill for rolling hot metal bars, to be powered by the smoke from the blacksmith’s forge:

The idea of using heat for mechanical work — and even industrial work — thus had a continuous, centuries-long history.

Steam Engines Suck

But that’s not why I was shocked by what I found in de Caus’s book. After all, the hollow rotating version of Hero’s aeolipile, despite being one of the least useful or sophisticated heat-using devices that even he describes, is mentioned by people all the time. It’s regularly trotted out in debates about why the Roman Empire didn’t have an Industrial Revolution, sometimes portrayed as a silly toy — a massive, unexploited opportunity — to support narratives about the Romans being, for some cultural reason, or because they had so much slave labour at their disposal, uninterested in industry or practical applications.

As any historian of science worth their salt will point out, however, the technological path to the steam engine didn’t really have to do with steam’s expansive force. In fact, the very opposite. Thomas Savery’s engine in the 1690s first sucked the water up a pipe, and only then heated it up to drive it further up. And Thomas Newcomen’s engine of the 1710s — the one that would become most used, and thus most famous — didn’t use steam’s expansive force at all. Steam was introduced into a cylinder under a piston, which was held up by a counterweight. That steam was then condensed with a spray of cold water, forming a partial vacuum under the piston. It was the suddenly massive relative weight of the atmosphere above this partial vacuum that did all the work. It’s why the Newcomen engine is also referred to as an atmospheric engine.

To get to this stage, the standard historical narrative — one that I’ve even given a few times myself — is that Savery and Newcomen were only able to do this because of a few crucial scientific discoveries over the course of the seventeenth century. The narrative usually goes something like this (heavily simplified):³

1. Evangelista Torricelli, one of Galileo’s disciples, experiments in Florence in the early 1640s using a thermometer and invents the barometer (we’ll come back to this later). He believes that he has demonstrated that vacuums are possible, and that the atmosphere has a weight, writing to a friend in 1644 that “we live at the bottom of an ocean of elemental air”.
2. Otto von Guericke, either independently or having heard of Torricelli’s experiment, c.1650 creates vacuums using a mechanical air pump. By 1654 he’s pumping out air from under a piston, and thereby using atmospheric pressure to lift extraordinary weights — by 1672, when he finally publishes his findings, he’s managed to exploit it to lift 1,200kg (2,645 lbs). Von Guericke even uses his discoveries to invert the wind-gun, making it vacuum-powered instead.
3. Throughout the 1660s and 70s, Robert Boyle, Robert Hooke, Christiaan Huygens and Denis Papin, work on creating vacuums more quickly under a piston. They improve the air pump, and also try exploding gunpowder under a piston, with the expanding air from the explosion able to leave through valves. As the pressure drops following the explosion, the piston is forced down by atmospheric pressure. But it can’t work for very many strokes, because of the build-up under the piston of gunpowder residue.
4. Then it gets a little murky. One of the strongest theories is that Denis Papin, after he invents the steam digester — essentially a pressure cooker — notes that he can turn it off and create a partial vacuum by condensing steam. Having initially just waited for it to cool down, his improved method is to immerse the heated cylinder in cold water. Papin himself fails to fully exploit this in his own attempts at an atmospheric engine, but he does publish his steam digester experiments in 1687. Not just in letters or a journal, or in academics’ Latin, but as a separate book in English.
5. Thomas Newcomen, plausibly, reads Papin’s book. We just don’t know much about him, unfortunately, but it’s a fairly compelling theory: one of his friends later even describes how he had been using a very similar-sounding cold-water jacket, but that the solder of the hot piston melted and the cold water leaked in.⁴ The accidental result of this direct injection of cold water? A speedy vacuum. After another decade or so of further improvement to iron out all the kinks, we have a practical, steam-condensing atmospheric engine.

Even if there’s a bit of a jump at the end because of how little we know about Newcomen, the steam engine is the classic example of an invention only made possible by science.

But here’s the thing. Although this may well be the chain of events in terms of how each person inspired one another, I’m now no longer sure that it was actually necessary. The thing that so shocked me when reading Salomon de Caus’s 1615 work was that, largely unnoticed by modern historians,⁵ he describes in great detail a solar-powered steam engine — not only one that exploited the expansionary force of steam, which so many others had since ancient times, but also, crucially, by exploiting atmospheric pressure too.

De Caus had — over 80 years earlier — already invented something very much like Thomas Savery’s 1690s steam engine, which you’ll notice I missed out from the standard historical narrative above. This is because Savery sits very awkwardly in it, skipping many of the steps while seemingly making a few leaps of his own. (Here, by the way, is the only accurate video I’ve been able to find of how it actually worked.)

Savery’s engine did exploit atmospheric pressure, so apparently made use of step 1. But his engine used the water that it pumped rather than using a piston to lift any weights, essentially ignoring steps 2 and 3. And Savery was ahead of Papin when it came to step 4 — not only did he use steam as his medium, but he condensed it by spraying cold water onto steam-filled vessels. Papin failed to exploit this in his own attempts to create an atmospheric engine, having to consult with Savery on how he had got it to work.⁶ As for the last step, Newcomen was allegedly unaware of Savery’s invention (they later teamed up to sell their engines together, under the absurdly broad umbrella of Savery’s patent, covering the “raising of water and occasioning motion … by the impellent force of fire”).⁷ Savery thus sits awkwardly parallel to the typical scientific narrative leading to Newcomen.

Now, some might argue that Savery’s engine was something of a dead end, almost immediately superseded by Newcomen’s more elegant solution. The Savery engine had very real limitations, failing to raise water from deep mines. There was a theoretical limit to how far it could exploit atmospheric pressure to “suck” up water from mines, in practice limiting that process to under 9 metres (~30 feet), and meaning that the boiler and apparatus would have to be placed deep within the mine itself. Its ability to then “push” the water even higher, by using the expansive force of steam, was then also limited by the kinds of pressures Savery could achieve with his boiler, and the ability of his pipes to handle them. Metallurgy still had a long way to go in the 1690s.

But the Savery engine was not a dead end. Although it failed when applied to pumping the water out of deep mines, it had all sorts of other uses — essentially, wherever water needed to be raised, but not too high. And it was significantly cheaper to make and install.⁸ It was used for fountains, used for draining marshes, for raising seawater for saltworks in Italy, for raising water to then drive waterwheels, and for raising water for domestic use in particular large houses or in towns. A Savery engine ran for at least a few years raising water at York House, to augment London’s water supply. And it continued to be improved. In the late 1710s in England, Theophilus Desaguliers and the visiting Dutch scientist Willem 's Gravesande greatly improved its efficiency.⁹ In the 1740s in Portugal, Bento de Moura fully automated all of its various clacks and valves. And the English engineer William Blakey installed them all over Europe in the 1760s-80s.¹⁰ The Savery engine was thus still in use and being developed, almost a hundred years after Savery unveiled it.

So that’s what makes the de Caus engine all so shocking. Savery’s invention was an important one, that was often adopted for practical use. It also seems entirely plausible to me that it could have been a sole source of re-adaptation, from which someone could eventually have derived a Newcomen-like invention — in other words, for a practical atmospheric engine to have been invented even if the traditional steps 1-4 had never occurred. And yet, Savery’s engine was seemingly not the first device to exploit the water-raising powers of condensing steam. Indeed, even de Caus in 1615 wasn’t the first — despite preceding the traditional narrative’s Step 1, Torricelli’s discoveries, by almost three decades.

Solar-Powered Steam Engines

Here’s what de Caus’s invention looked like (you can read the full work in French, here):

In this basic version de Caus has four copper vessels with some water in them, and connected through their bottoms with pipe (P). A valve (H) allows them to draw up water from a cistern below, without that water falling back down. And another pipe (F) goes into the water in each of the vessels, so that water can be pushed up through another valve into a fountain. The way it works is deceivingly simple. When the hot midday sun warms the vessels — de Caus mentions this will work best in a warm country like Italy or Spain — the air and water will heat up in the vessels, forcing the water up to make the fountain flow.

Then, and this is the crucial bit, “after the heat of the day has passed, and night falls, the vessels in order to avoid emptiness will attract the water from the cistern, through the pipe and valve H and P to refill the vessels as they were before”. He even fully appreciated that the condensation could be achieved with cold: “the said vessel will refill with water when night becomes, because of the coolness of the air”. Atmospheric pressure in action, without even the concept of the atmosphere having a weight. In fact, without even the concept that a vacuum is possible. De Caus thought of his solar-powered fountain as exploiting the impossibility itself — that nature’s horror of a vacuum was so strong as to perform wonders.

And de Caus developed it further. In order to increase the heat and increase the strength of the fountain, he changed the shape of the vessels and added convex glass lenses into their walls, to focus the sun’s rays on the water within. He even included a recipe of how to make a special cement fixing the glass to the copper that wouldn’t melt with the heat — when you see such an incongruous detail in a book of this kind, it’s a very strong indicator that he actually made at least one working model. If that failed to work, he suggested an alternative approach: to use a frame of convex glasses that would then focus on the surface of the vessels, rather than being integrated into the vessels themselves. And he suggested alternative applications. Because de Caus was obsessed with music, he used the same principles to have a statue seem to make a sound when the sun shone. It was something he’d read about from ancient times — in Roman Egypt, a statue of Memnon was supposed to have done just that.

It may sound like de Caus’s machines were trivial amusements, only operating at a certain time of day, as a sort of trick for fountains and music. True. But he was certainly interested, in more general terms, in industrial applications for machines — the rest of the book includes drainage pumps, a way to put out fires, machines to bore wooden pipes, and an astonishingly sophisticated lathe. It was not that large a leap for him, surely, to have already started to think about how to apply heat and cooling more generally to such devices, and not only using the sun. He even hints at how “it is possible to make many more admirable inventions with this machine, which I will look at another time.”

Unfortunately, he didn’t get around to publishing a proper follow-up, but it’s obvious that he knew he was onto something special. In the book’s dedication, the only machines that he singles out for comment are those “which can be agitated by the sole means of the temperature of the air, which comes to heat up by means of the sun, or to cool down by its absence” — again with the vague promise that many admirable things might be done with such machines.

So we have a conundrum. A machine with the same core concept as Savery’s steam engine — but far too early to have been influenced by the science of Torricelli, von Guericke, Huygens, Boyle, or Papin.

Where did de Caus get the idea? And did anyone take them further in the 80 years between him and Savery? We’ll look at that next time in Part II.

1. Luke Morgan, Nature as Model: Salomon de Caus and Early Seventeenth-Century Landscape Design (University of Pennsylvania Press, 2007), pp.7-18

2. Lynn White (Jr.), Medieval Technology and Social Change (Oxford University Press, 1964), pp.91-4

3. e.g. Graham Hollister-Short, ‘The Formation of Knowledge Concerning Atmospheric Pressure and Steam Power in Europe from Aleotti (1589) to Papin (1690)’, in History of Technology, ed. Ian Inkster, vol. 25 (London: Bloomsbury Publishing, 2004), pp.137–50.

4. David Wootton, The Invention of Science: A New History of the Scientific Revolution, First Edition edition (London: Allen Lane, 2015), pp.504-5

5. Wootton, for example, briefly mentions it on p.491, but mistakenly assumes that it only used the expansionary force of steam.

6. Ibid., pp.495-7

7. See Patent no.356.

8. John Farey, A Treatise on the Steam Engine: Historical, Practical, and Descriptive (Longman, Rees, Orme, Brown, and Green, 1827), p.116.

9. Ibid., pp.111-15

10. Lissa Roberts, ‘Full Steam Ahead: Entrepreneurial Engineers as Go-Betweens during the Late Eighteenth Century’, in The Brokered World: Go-Betweens and Global Intelligence, 1770-1820, ed. Simon Schaffer et al. (Science History Publications, 2009), pp.193–238