James Watt - Britain's Greatest Mechanical Engineer?

Scottish engineer James Watt is famous as a founding father of the Industrial Revolution. 2019 is the 200th anniversary of his death. The Bank of England are commemorating his achievements by featuring him (right) on the £50 note, the last ever British note to be printed on paper. We will commemorate by investigating his bona fides, then go on a tour of the places he lived and worked.

About steam engines

First, we need to explain briefly about steam engines. Everyone knows that they drive pistons which connect to something that converts the reciprocating movement into linear or rotary drive. What most people do not realise is that early steam engines did not push the piston with expanding steam but pulled it with condensing steam. The preference for this technique is that cylinders at the time were made by rolling a flat sheet of metal into a cylinder then welding the join. Early experiments with expanding steam showed that the high pressure was liable to split the welded joint, with explosive consequences. The worst that can happen with a condensing engine is that the system implodes safely.

All commercial steam engines up to 1800 were of the low-pressure condensing design. Before Watt, they were of a type designed by Thomas Newcomen in the early 1700s. Their operation is demonstrated in the Wikipedia animated GIF below. If the piston starts at the bottom of its stroke, a weight on one end of a beam pulls up a piston attached to the other end. It sucks in low pressure steam from a vat of boiling water. Steam fills the cylinder as the piston withdraws. At the top of the stroke, a valve shuts off the steam and cold water is injected into the cylinder, thereby condensing the steam forming a vacuum. Atmospheric pressure pushes the piston back in. As it nears the bottom of its stroke, the steam valve opens again to allow the condensed steam to drop back into the vat of boiling water. When the cylinder reaches the bottom of its stroke, the process repeats. Air pressure does most of the work, which is why these were usually known as 'atmospheric engines'.

Watt's key innovation was an improvement to the condenser. Newcomen engines condensed the steam by squirting cold water into the piston cylinder. Watt realised that this cooled the piston and the piston cylinder. They drew energy from the steam on the next cycle, making the system fuel inefficient and less powerful than it could be. Watt's idea was to condense the steam in a separate chamber. His engine has a valve that opens when the piston is at the top of its stroke to allow steam to escape into a separate condensing chamber that receives the cold water to condense the steam and create the vacuum. The Bristol University GIF below shows how it works. Watt's basic engine was twice as fuel efficient as even the most sophisticated Newcomen engine.

Watt invented the separate condensing chamber in 1765. He received his patent in 1769. He did not have the money or skills to develop his invention, so he formed a partnership with Clyde-based English entrepreneur John Roebuck. Roebuck provided capital and access to his Carron iron foundry for manufacturing components.

For the next ten years Watt tried to build a full-size steam engine, but was constantly thwarted by an inability to get his pistons and piston cylinders made to the required precision. In 1774 Roebuck went bankrupt.

Roebuck's patents were acquired by English entrepreneur Matthew Boulton. Boulton had specialist iron workers at his 'Soho Manufactory' that were able to make precision parts and he knew of John 'Iron-Mad' Wilkinson's technique for precision boring cast-iron cannons. This technique was perfect for making Watt's cylinders. The three of them produced the first successful Watt steam engine in 1776. It was used in Wilkinson's factory. Boulton got the patent extended until 1800. They all became very wealthy.

Over the next five years, Watt improved his design, most notably by a 'double acting' system that alternately condensed steam on both ends of the piston head. By 1782 the Watt steam engine was five times as fuel efficient as the most efficient Newcomen engine and more than twice as powerful.

James Watt's momentousness

James Watt is often said to have invented the steam engine. It is a fallacy. Steam power had first been harnessed back in the 17th century by Thomas Savery. Newcomen combined Savery's steam pump and Papin's steam piston into the first working steam engine in 1712, 24 years before Watt was born.

Watt's main contribution to steam engine technology was the separate condenser, which more than doubled steam engine fuel efficiency. Watt may also have been the most brilliant engineer this country has ever produced, although he hid his light under a bushel, so it is difficult to be sure. In his youth he worked at the University of Glasgow. Even though he was not an academic, physicist John Robison thought him the smartest person on campus, which is impressive when others included Joseph Black, Adam Smith and himself.

Robison said of Watt: "When to the superiority of knowledge in his own line, which every man confessed ...", which is to say that Watt knew more about the subjects being taught than the professors that taught them. Sir Humphry Davy was another fan: "Those who consider James Watt only as a great practical mechanic form a very erroneous idea of his character; he was equally distinguished as a natural philosopher and a chemist, and his inventions demonstrate his profound knowledge of those sciences, and that peculiar characteristic of genius, the union of them for practical application."

No one has a bad word to say about Watt's character either. Robison expressed a common opinion of him: "I have seen something of the world and I am obliged to say that I never saw such another instance of general and cordial attachment to a person whom all acknowledged to be their superior. But this superiority was concealed under the most amiable candour, and liberal allowance of merit to every man."

Lots of brilliant people have never achieved greatness or momentousness. Watt's condenser was a simple and minor improvement to a proven technology. He said himself that: "when it was analysed, the invention would not appear so great as it seemed to be". He was humble and self-effacing, but on this occasion he was not being overly modest. If Watt had not invented the separate condenser when he did, someone else would have done so within a few months. If he is to rank among the greatest or most momentous British engineers, it has to be through his other achievements.

In 1780, Watt invented the copying press. It was simple and ingeneous. A chemical was applied to an inked document to reactivate the ink. The document was then pressed against a special type of transparent blotting paper to get a mirror image which could be read through the paper. It became the standard way to copy documents for 100 years.

Watt's other important invention was the 'Double Acting Engine', which condensed steam on both sides of the piston head, thereby boosting its power and fuel efficiency. Or, at least, most people assume that Watt invented it because he filed the patent. We discuss this in our blog about William Murdoch. It turns out that Watt filed most of B&W's patents up to 1790 because he was a partner whereas his brilliant Chief Engineer William Murdoch was just an employee. Subsequent correspondence shows that Murdoch devised nearly all the inventions at B&W after 1779. There is no surviving correspondence about the Double Acting Engine but this seems to be because James Watt's son destroyed it all, perhaps trying to protect his father's legacy. Watt senior did write about his pride in his invention of the 'Parallel Motion' linkage for the Double Acting Engine without saying that he invented the idea or its other components. It seems to us that Murdoch probably invented it and pretty much everything else that B&W patented after 1779.

James Watt effectively retired from Boulton & Watt in 1800, when his condenser patent expired. He kept tinkering with other inventions. One of these was the articulated water main, which he invented to help Thomas Telford pump fresh water across the Clyde. He says that he got the idea from a lobster's tail. He filed dozens of patents while in semi-retirement. Most of them were complete duds.

In retirement, Watt dedicated more time to the Lunar Society, a monthly meeting of the most brilliant businessmen, scientists and engineers in the country. Following a discussion with Joseph Priestley, another member, about Henry Cavendish's groundbreaking experiments on the nature of water, Watt is often credited with having discovered the compound nature of water. At the time, it was thought to be an element. Watt was indeed the first to publish a theory that water is a compound. But this is not the same as discovering it. He performed no experiments to support his theory and his understanding was hugely flawed by his belief in the phlogiston nature of air. Lavoisier reran Cavandish's experiments independently of Watt. He made the momentous discovery about the exact chemistry of water and it is his terms we use. Watt's contribution was little more than a perspicacious guess. No one denies that he was very smart.

Richard Trevithick patented the high pressure steam engine in 1802. It was smaller, more powerful and more fuel efficient than condensing engines. Sales of condensing engines plummeted, although some pumping engines still used them into the 20th century. Few parts of the condensing engine were retained in high pressure engines. Watt's condenser was made obsolete. It had a useful life of just some 30 years.

Watt's achievements, condenser aside, are therefore linked to the business created by his condenser patent, which gave Boulton and Watt control of the steam engine industry for 25 years. They were a safe pair of hands. Less scrupulous businessmen might have sacrificed safety and quality for short term profit. This might well have led to explosions that could have set back steam engine deployment by decades, and perhaps forced the industry overseas. Boulton and Watt used their monopoly status to ensure that steam engines were deployed rapidly, widely and safely for myriad purposes. Eventually they did make a lot of money out of it. Their patriotism ensured that subsequent steam engine advances were made in Britain and that Britain benefited from them first. They left a wonderful engineering legacy in Britain that persists through to the present day.

This said, Boulton and Watt's business was lucky. They offered James Keir the opportunity to become a partner in 1778. He declined after reviewing the accounts, on the basis that they were taking a lot of risk and not making any money. In 1780, B&W was still not making any money. Worse, their core mining market was becoming saturated and former employees were driving down prices by starting up in competition. Then Boulton was approached by James Pickard who had adapted Newcomen engines for rotary motion by linking the piston to a crank. The potential market was huge and far more lucrative but Pickard had a patent. He offered B&W a cross license. Boulton refused. Instead he asked Watt and William Murdoch to find an alternative way to drive a rotary gearchain. Murdoch came up with the Sun and Planet gear. It re-invigorated the company's fortunes.

Watt had a particular type of brilliance, exactly as Sir Humphry Davy said, in the ability to quickly absorb the theoretical and practical implications of new technologies and techniques. His membership of the Lunar Society gave him early access to the latest scientific breakthroughs and technological innovations. And he lived at a time when the world was full of technology open goals. They just needed someone smart to think about satisfying the need. Watt had the intellect, the wealth, the inside information and the opportunity to have devised dozens of fabulously successful devices. In practice, he devised only three.

Why did Watt not invent more useful devices? Poor health did not help. He was a sickly child, understandably mollycoddled by his mother who had lost her previous two children. He grew up to be a hypochondriac, prone to headaches, depression and drug dependency. Like Charles Darwin, he lived in constant fear of imminent death. It is difficult to be positive or inventive under such circumstances. Two character traits also worked against him.

One was a lack of business acumen. He was embarrassed by money, disliked talking about it and hated quibbling about it. The other was a natural caution. William Murdoch was keen to experiment with high pressure engines 20 years before they were patented by Richard Trevithick in 1802. Watt held him back, thinking that steam boilers of the day were too flimsy for high pressure engines to be safe. He should have had more faith in Murdoch's ability to mitigate the risk. Trevithick was an engineering minnow compared Murdoch. If Trevithick could make safe high pressure boilers, Murdoch definitely could. We agree with John Griffiths' assessment that Watt probably held back the transition to high pressure steam engines by at least ten years.

This was not the only occasion when Boulton and Watt held back steam engine progress. They used their patents to stifle competition throughout the last 20 years of the 18th century, most notably against Hornblower's compound steam engine. Indeed, safety aside, there is a good argument that Boulton and Watt had a net negative impact on steam engine progress.

It has to be said that, even before Murdoch came up with the Sun and Planet gear, Watt was incredibly lucky. The idea of the separate condenser came to him after being asked to fix an inefficient miniature steam engine. He would not have realised that a separate condenser would fix it, were it not for his friendship with Joseph Black. His separate condenser would probably have lapsed without his chance partnership with Roebuck. It would probably have lapsed if Roebuck had not gone bankrupt, which was by sheer bad luck. It would probably have lapsed if anyone other than Boulton had acquired Roebuck's patents. It would probably have lapsed if John 'Iron-Mad' Wilkinson had not devised his cannon-boring technique at the right time or if Boulton had not known about it. And, even though all these things did happen, Watt was very fortunate not to have been swindled out of his rewards, because he shared his idea with lots of people, any number of whom could have blabbed before it was patented, and because he was a notoriously poor businessman.

In summary, Watt had the intellect, talent and opportunity to have been Britain's greatest mechanical engineer, but he failed to live up to his potential. He does not even make our Top 10. But he is more momentous than great. He provided the opportunity, environment and encouragement for William Murdoch to thrive. Boulton & Watt dominated steam engine design and production for 25 years. Their caution and professionalism ensured that the transition to steam power was safe, fast and relatively efficient. They helped Britain build a critical mass in these endeavours that allowed us to grow rich and powerful right through to the First World War. The SI unit of power is named after him. We think he just about deserves five global momentousness medals.

James Watt pilgrimage

Some of our hero tours have many interesting places to visit. James Watt is not one of them. The two places he spent the vast majority of life, Greenock and Soho/Handsworth, have changed out of all recognition since his day. The only surviving places he is known to have spent any significant amount of time are his workshop in Kinneil, two houses in Cornwall and the homes of fellow Lunar Society members. We will return to these in a forthcoming blog about the Lunar Men.

James Watt was born into a prosperous middle-class family in Greenock. His parents were Presbyterian Covenanters with a passion for probity. They lived in a comfortable house at the junction of Dalrymple Street and William Street in Greenock. There is a statue of him in William Street (above) which claims to have been built on the location where he was born. It seems plausible. We asked the locals what exactly Watt is depicted doing on his statue. No one knew. It looks like he is working out how best to stab a piece of toast with the leg of a theodolite stand, but we guess he must be testing one of his inventions, presumably his reflecting distance measuring device.

Watt was a poorly child, too feeble for the rough and tumble of school, in the opinion of his parents. They were both well educated, so they taught him at home. Eventually, he attended Mr McAdam's private school. He hated it. After a bout of illness, he went to Greenock Grammar School aged 14 (Inverclyde Council say 13), where he showed a proficiency for maths and engineering. Neither of the buildings survives.

There was a Watt family pew in the Old West Kirk at Greenock, which James presumably attended as a child. The church building survives but the pew is lost and the stones were moved to a different location in the 1920s. Nothing else survives from Watt's early life. There are a couple of buildings in William Street that look like they would have been there in Watt's day, but there is no record of Watt having visited them.

Watt's father, also James, ran a joinery and chandlery, servicing ships that used the nearby pier. In the evenings James junior used to repair nautical instruments in his father's workshop. He decided to try this as a career. At 18 he went to London to learn mathematical instrument repair professionally. Watt's apprenticeship was to a mathematical instrument maker named John Morgan of Cornhill. No one knows exactly where it was, and the entire street has been redeveloped several times since.

A cairn (below) dedicated to Watt was erected in Greenock Cemetery to commemorate the 200th anniversary of his birth. It is constructed of rocks from all over the world but there is nothing underneath.

Watt fell ill while working in London. He was forced to return to Greenock in the Autumn of 1756. Once he had recovered, he went to Glasgow to look for work. The local Guild prohibited him from opening a shop. Instead he found work repairing instruments for Glasgow University. He was given a workshop and lodgings inside the University. His customers and visitors included Dr Joseph Black, the eminent Scottish chemist who went on to discover magnesium, carbon dioxide, latent heat and specific heat; John Robison, first General Secretary to the Royal Society of Edinburgh; Adam Smith, the founder of economics; and William Small, who taught Benjamin Franklin.

Smiles describes the workshop's location as being: "In the inner quadrangle, entered from left hand side of the outer court." He goes on to explain: "It was situated on the first floor of the range of buildings forming the north-west side of the inner quadrangle, immediately under the gallery of the Natural Philosophy class." That building was beside Blackfriars Church, some way from the modern campus. It was demolished in Victorian times. From the orientation of the church, Watt's workshop should be at the location indicated on the 1650 etching above. By our reckoning, it is under Aldi to the east of the High Street.

In 1759, the aforementioned John Robison, then only 20, suggested to Watt that they try to build a steam powered carriage. Watt knew nothing of steam technology. There was only one steam engine in the whole of Scotland at the time. He went off to learn about it by building his own high pressure and low-pressure models.

Meanwhile, Watt's instrument business was still tied to the University. In order to grow, he needed a more central location. He therefore formed a partnership with John Craig, who provided capital, to open a retail outlet in Saltmarket, opposite St Andrews Way. In 1762 he moved to bigger retail premises in Buchanan's Land on the north side of Trongate. A plaque marks the location of his workshop. By this time he was employing 16 staff. The business was successful enough for him to buy a house in Delft Field Lane (below) and to get married. As with nearly everything from Watt's formative years, the shops and his home in Delft Field Lane, now renamed James Watt Street, have gone. 

In 1763 (Inverclyde Council say 1765), Watt got his hands on a miniature Newcomen engine that belonged to the Natural Sciences Department of the University. It was inefficient, only managing a few strokes before getting stuck. Watt realised the problem was that the cylinder and piston were being cooled when the steam was condensed. He worked out the cause was the relatively large amount of cold water needed to condense a relatively small amount of steam. His friend Joseph Black explained this was due to his recent discovery of 'latent heat'. The miniature Newcomen engine (below) is now in Glasgow's Hunterian Museum, and always on display.

For the next two years Watt pondered and experimented with steam engines, looking for a way to make the Newcomen design more efficient. He reflected later that he: "groped in the dark, misled by many an ignis fatuus, but nature has a weak side, if we can only find it out". Then the answer came to him while out walking one Sunday in May 1765. He says that he entered Glasgow Green by the gate at the bottom of Charlotte Street and that the separate condensing chamber solution had formed in his head before he got the 'Golf-house' (golf was being played on Glasgow Green from at least 1721). The golf course has gone, but there are two pillars which mark the spot where the gate used to be. It is a bit disappointing, but this is the earliest surviving place where James Watt definitely stepped foot.

Some 200m south of the Charlotte Street entrance, just on the far side of the Nelson Memorial, is an inscribed boulder (below). It says that this is roughly the place where Watt devised his separate condensing chamber. It is pretty much where we would have put it too.

Some 500m southeast of the boulder is a slightly comical statue of Watt (below) looking like Bilbo Baggins. We presume that is a condensing cylinder under his elbow. At least it he was not wearing his usual traffic cone when we saw him.

Following Watt's eureka moment, he started making miniature models of his condensing engine. The problem came when he wanted to scale it up into a working machine. The cost was beyond his financial means and the iron-workers in Glasgow were smiths, whose skills were unsuitable for precision engineering. Watt's friend Joseph Black lent him some money to get started. Meanwhile, Watt's instrument making business partner died. He closed his retail outlet and took up surveying, at which he was talented and fairly successful, though not successful enough to fund the construction of a working condenser.

Joseph Black cast around for someone that could help him on both counts. He came up with English entrepreneur John Roebuck, who was in Scotland trying to extract coal from a mine that kept flooding. Its Newcomen engine was not powerful enough to pump the water out. Roebuck had capital and an incentive to get a more powerful steam engine. He also owned the Carron iron foundry, which employed higher skilled iron workers than Watt had been using. Roebuck was based near Bo'ness. It was only 35 miles from Glasgow, but before the days of scheduled transport. Roebuck and Watt started corresponding.

Watt sent specifications to Roebuck for items to be engineered at Carron. These were returned in boxes to keep them secret. They were better than anything Watt had produced in Glasgow, but not good enough. In 1767, Watt and Roebuck entered a partnership in which Roebuck paid for a patent application, paid off Watt's debts and provided future development funding in exchange for two-thirds of Watt's future patent revenues.

Watt's patent was granted in January 1769. He moved into a workshop behind Roebuck's Kinneil House at Bo'ness. Remarkably, this workshop survives (below - Historic Scotland have put a plaque on it since we were there). It was found with some of the engine parts that Watt was working on when he left. Kinneil House is operated by Historic Environment Scotland. The grounds, including Watt's workshop, are open almost every day. Entry is free. As far as we know, this is the only place in Scotland that is unchanged since Watt's time and the only place in Scotland that gives an idea of what Watt would have experienced.

Watt completed his first separate condenser engine in September 1769. It was not a success, with steam leaking between its poor fitting piston and cylinder. By this time Watt had run out of money. He reverted to surveying work to make ends meet, tinkering with his steam engine when he had time. Several more trial engines were built. They all failed. And always because of inexpertly bored/hammered cylinders and inexpertly hammered/turned pistons. Watt experimented with lots of different materials to seal the piston in the cylinder. None of them worked.

During all this time Watt was corresponding with his friend William Small. Small had spent seven years teaching in America, where one of his pupils was Benjamin Franklin. Franklin subsequently came to Britain and made friends with Matthew Boulton. Boulton was also a supplier to Watt's business partner John Roebuck. When Small returned to England in 1764, Franklin introduced him to Matthew Boulton and he settled nearby. He became Erasmus Darwin's physician. Boulton and Darwin invited Small to join the Lunar Society. Small encouraged Watt to visit Boulton, because he knew that Boulton's Soho Manufactory had better iron working skills than anything available in Scotland. Watt visited Soho twice, meeting Boulton on the second occasion. He tried to persuade Boulton to buy into his partnership with Roebuck, but Boulton was busy with other projects.

In 1774, Roebuck went bankrupt. He owed Boulton £1200. Boulton agreed with Roebuck's creditors to take Roebuck's share of Watt's patent in lieu of payment. Watt's wife had died the previous year in childbirth. He was frustrated at the lack of manufacturing skills in Scotland and by the low rates of pay for surveyors. He loathed the Scottish weather, which played havoc with his weak constitution. He was planning a move to England anyway. Becoming a business partner with Boulton gave him the shove. He arrived in Birmingham in May 1774.

Watt sent his most recent prototype engine to the Soho Manufactory in bits. Boulton and Watt immediately set about reconstructing it. The Soho staff got it working better than it ever had done in Scotland, but even they could not hammer the cylinder accurately enough to prevent steam escaping. Boulton knew of 'Iron-Mad' Wilkinson's precision cannon boring technique. While Watt was in London trying to secure an extension to his patent, Boulton commissioned Wilkinson to make a new cast-iron bored cylinder. A 24 year patent extension - to 1800 - was approved by an Act of Parliament in May 1775. When Watt returned to Soho, Boulton had just received Wilkinson's 18-inch cast-iron precision bored cylinder. It worked brilliantly.

In August 1775 (according to Smiles), Watt moved into a lovely three-story five-bay house belonging to Boulton in Regent's Place, Harper's Hill. He brought his two children down from Scotland to join him. It was demolished long ago. There is a plaque in Regent's Place (above) above the door of number 17, now Deakin & Francis, marking it as the location of Watt's home between 1777 and 1790. If Smiles is right, the occupation date is wrong and it should have been on the other side of the road and further east, perhaps around number 53.

Matthew Boulton's Soho Manufactory was demolished in 1863. It used to lie south of Factory Road in Birmingham and west of Hockley Brook, roughly where the Motor Body Centre & Recovery is now located. The Soho Foundry (above) survives nearby. Watt visited the foundry most days and it is where William Murdoch worked for his first two years at Boulton & Watt. It is now an Avery weighing machine factory. They once escorted visitors around Murdoch's cottage and a small B&W museum, but that stopped long ago. On our 2021 visit, we found the outside covered in scaffolding and looking very sorry for itself.

On our 2021 visit, we stopped off to check the 'Golden Boys' statue of Murdoch, Boulton and Watt (l-r) which we last saw in Centenary Square. It seems to have disappeared  again. Hopefully, it will come back in time for the Commonwealth Games.

Watt's next mission was to design an engine specifically for pumping water from mines. He went to the tin mines of Cornwall, which Boulton expected to be the biggest customer because they had no coal to fuel steam engines. In 1777 he revealed his single-action pumping engine. It was an immediate success. Sales were brisk enough for Watt to rent accommodation at 12 Plain-en-Gwarry in Redruth (the left-most of the cottages above). We assume it is the same building, although it is a little odd that it does not have a plaque.

Boulton and Watt's engines were so successful in Cornwall's tin mines that they needed more permanent accommodation. They settled upon Cusgarne House near Truro (above). It still exists, little altered.

In 1790, Boulton recommended to Watt that architect Samuel Wyatt design and build him a house near to the factory. The result was Heathfield Hall in Handsworth. Watt lived there until his death in 1819.

Heathfield Hall was demolished in the 1930s, but not before the entire contents of his attic workshop had been transferred to London's Science Museum, where they are still on display (above). Most of Watt's other surviving possessions are there too. When we last visited it in February 2019, a display cabinet showed tools he used in his instrument making business, including an unusual micrometre, some chemicals he used for later non-steam experiments, and some musical and mathematical instruments that had he repaired.

James Watt is buried in St Mary's Church, Handsworth. We looked around the graveyard for his headstone but could not find it, only to discover that the church had been extended over it. His grave is now inside the church. Boulton and Murdoch are buried outside. Each has a nice bust in the nave.

One other important James Watt bust is in the Hall of Heroes in the Wallace National Memorial near Sterling. He is third left, just beyond William Murdoch.

The only other places that Watt is known to have spent a lot of time were the Lunar Society meeting venues. Watt was an active and popular member, attending most of the meetings. The Lunar Society is one of our favourite subjects. We will write a blog about it as soon as we get a chance. The surviving venues, for those that are interested, include Soho House (above) which was Matthew Boulton's home, Darwin House in Lichfield where Erasmus Darwin lived, Bowbridge House in Mackworth and Great Barr Hall in Great Barr.

We wanted to visit every surviving Boulton and Watt stream engine that the great men might have worked on (i.e. excluding those made by their sons for Boulton & Watt Co.). As far as we can tell, there are only two working Boulton and Watt engines left in the world. One is in Australia. The other is the 1779 Smethwick Engine (above), currently at Thinktank Museum in Birmingham. Apparently they had it running for the public in November 2018, but we missed it. The oldest surviving Boulton and Watt steam engine - well, the pistons, cylinders and beam from it - is 'Old Bess' - presentation plaque below - built in 1777, which is on permanent display at the Science Museum in London. They have another complete engine from 1788. There is also a 1786 rotary engine, with a wonderful sun-and-planet gear, in the National Museum of Scotland. As far as we know, that is all.