The Star Drive

The True story of a Genius, an Engine and Our Future

Phillip Hills

• Publisher: Birlinn
• Year: 2021
• ISBN:
  9781788853002
• Topic: History
• Subtopic: 19th Century History
• Index: History

In May 2018 NASA called a press conference to announce the successful test-run of their tiny nuclear reactor KRUSTY (Kilopower Reactor Using Stirling Technology). This revolutionary technology, which runs on heat alone, may have profound consequences for the future of mankind, enabling us to maintain permanent bases on the Moon, on Mars and other planets, and eventually power a starship. On earth too it could have enormous benefits as a new way to generate power at a time when climate change is threatening our very existence. This book is the amazing story behind this invention, which began with Robert Stirling’s original designs for a heat exchange engine in 1816. An invention truly ahead of its time, the practical application of the Stirling Engine has taxed the minds of scientists and inventors for almost 200 years. Only now is it possible for its full potential to be realised. Phillip Hills weaves science and history together to tell the story of one of the most exciting scientific developments the world has ever seen.

CHAPTER 1

Robert Stirling

The summer was bad that year, and it was bad all over. There were frosts in the spring, and in some places there was snow in June. There was frost again in August and the crops rotted in the fields. Farmers who had poor harvests thought themselves fortunate, for most had no harvest at all. The wheat crop failed; so did the potato. Even the oats, that hardy cereal which had evolved in northern climes, were mostly not worth the trouble of raising from the mud in which they lay. The sun was rarely seen, and when it was, it was blood-red. The rain never seemed to stop. It was the worst summer, by far, in nearly two thousand years.

The date was 1816 and the whole of the northern hemisphere was affected. The weather had been bad for some years past: most people had eaten their reserves of corn and there was nothing left. Famine crawled the land: across Europe, Russia, China and North America people and livestock died. More in some places than in others, but everywhere there was distress. The cause, as we now know, was a series of volcanic eruptions from 1812 onward, culminating in the eruption – or, rather, the disintegration – of Mount Tambora in what is now Indonesia. It was the biggest blast in recorded history – bigger by far than the sum of all the nuclear explosions since 1945. An aerosol of sulphur compounds was hurled into the stratosphere, the sunlight was dimmed and global temperatures dropped by about one degree Centigrade. That is a lot more serious than it sounds.

In an age of widespread belief in supernatural agency, people understandably applied to their god or gods for relief, though none seemed disposed to help. In the Laigh Kirk in the town of Kilmarnock in Scotland, the congregation looked on the bright side and thanked the Lord that their church had been rebuilt a few years before and at least the roof kept out the eternal rain. But, being good Calvinists, they regarded the foul weather as divine retribution for their – or at least for their fellows’ – sins. Such views were becoming less common among the more educated part of the populace, due to the influence of Enlightenment rationality in the preceding half-century. But even in the less-evangelical churches, a great many people clung to the notion that by amending their evil ways or, more commonly, by persuading their fellows to amend theirs, they might induce the deity which governed the universe to suspend the operation of causality in their favour.

In this they showed a certain lack of perspective, which is not uncommon in religious congregations of all denominations. The idea – that the deity might be persuaded to undo the effects of a few million tons of Mount Tambora dispersed in the stratosphere, in return for improved behaviour on the part of the townsfolk of Kilmarnock – seems disproportionate from our standpoint. It was not, apparently, from theirs. Prayers were offered up for better weather and promises of amendment were made.

In fairness to the Almighty, it must be admitted that the Kilmarnock folk didn’t keep their side of the bargain, so they couldn’t really complain. No doubt the promises were sincere at the time they were made, but the Minute Book of the Laigh Kirk session for the following year suggests otherwise. It shows the number of children born out of wedlock to have been slightly greater than before. (The Minute Book implies that there was little sin in Kilmarnock other than fornication. Since this would be viewed more tolerantly today, perhaps the Almighty’s reluctance to reverse the Mount Tambora event is understandable.)

In 1816 the Kirk of Scotland was not short of ministers ready to attribute failed harvests to human sinfulness, but their number was diminishing with the entry to the profession of young clergymen who had imbibed the philosophical and religious precepts of the later eighteenth century. The young man who had recently been called to the second charge in the Laigh Kirk was one of the latter; his name was Robert Stirling. His tenancy of the position was proposed in June and ratified in September. By the time he took up his duties, the dire condition of the country had become very obvious. We know from his actions and his later sermons that his inclination was rather to address a problem than to blame it on divine retribution for supposed immorality. Even so, what he did next was rather surprising: a week after his ordination he lodged an application to patent a device which would later be called a ‘heat exchanger’.

The purpose of the heat exchanger was to economise in the use of coal in furnaces by using the waste heat from the furnace flue to heat the air coming into the fire. (A fire which is supplied with hot air burns hotter than one which has to heat the incoming air.) It did this by doing what heat exchangers have done ever since: the cold incoming air is made to flow past the outgoing gas, smoke, etc. with only a thin wall between them. The heat is conducted through the wall from the latter to the former. It works both as a heater and as a cooler, depending on your point of view. The radiator of your car is a heat exchanger in which the heat from the engine cooling water passes through thin tubes and is transferred to the air which blows through it. Your central heating boiler passes the heat from burning oil or gas to the water which heats the radiators. The latter are also heat exchangers, since they transfer the heat from the water to the air of the room.

The Stirling heat exchanger invention was later to become important in the development of the steel industry and on that account alone the new minister of Kilmarnock kirk may lay claim to a place in industrial history. But it is with the second part of the patent application that we are concerned, for it describes an engine which, using modifications of his invention, might be applied to moving machinery. The application includes a drawing of the engine and from this, as well as the text of the application, it is apparent that Mr Stirling had more things in mind in the years preceding his ordination than theology and divinity.

Robert Stirling knew about bad harvests, for he had been a farm boy. Cloag Farm, where he was born, in the parish of Methven, near Perth, lies on the south-facing slope of the Grampian Mountains, overlooking the valley of the River Earn. The farm is still there today, as is the grey stone farmhouse which is almost certainly his birthplace. It is a fine if modest stone house set in tall, mature timber; prosperous but without ostentatious signs of affluence. The Stirlings were an extended family of middle-class agriculturists whose farms were strung across that southerly slope from Stirling to Perth. They were mostly tenant farmers, but nonetheless possessed of capital sufficient to stock and work a farm – which put them well above the labouring classes, both socially and economically. And the family was cohesive, each member being aware of the number and extent of his or her relations. Among Lowland families there was no formal clan structure such as that which prevailed in the Highlands (which began only a few miles north of Strathearn), but the Scots were notorious for their pride in, and adhesion to, family.

The land which his father farmed had been mostly forest as little as a century earlier, and what had not been woodland was bog. But from the early eighteenth century, a spirit of inventiveness and a habit of rational exploitation of possibilities of improvement had led to a huge increase in the fertility and productiveness of the land, and a rising population in growing towns and cities provided markets for agricultural produce. It was a virtuous circle which made possible the developments in science and technology which were shortly to produce the second stage of the Industrial Revolution.

By the time Stirling was born in 1790, Cloag Farm had introduced new crops, some from overseas, which had been selectively bred to produce higher yields than the old varieties; methods of tillage had changed and machinery had reduced the need for human or animal muscle in planting, harvesting and processing. The machinery was mainly made of wood and would be barely recognisable as machinery today, but the principles on which it operated were coming to be understood throughout the farming community. Stirling’s grandfather was reputed to have invented a threshing machine, probably horse-powered, which separated the seed from the stalk and replaced the ancient flail. Machinery was driven by water, wind or animal power. (The steam engines which had become common in industry by the time of Robert’s birth were too big and too expensive for farm or village use.) In 1790 in the village of Methven, which lay at the foot of the slope below Cloag, there were several mills. The term ‘mill’ may be misleading here, implying as it does buildings of the dark satanic variety. Village mills were not like that: they tended to consist of cottages, in one end of which the operative pursued his or her craft, while the family lived in the other end – an arrangement sanctioned by tradition, but with cattle replaced by loom or spinning wheels. But they did contain machinery, of however simple a sort. The two-handed spinning wheel introduced in 1770 doubled the productivity of the spinner, thanks to a device which, though easy to make and to handle, introduced people to the notion that mechanical innovation might greatly increase their prosperity. As a consequence, young Robert grew up in a society whose fabric was shot through with the idea that life could be improved by the application of energy and ingenuity.

At the age of fifteen, young Stirling went from Cloag to Edinburgh – probably on foot, a matter of 50 miles or so. (In those days, most people did not stray far from home for most of their lives; and, unless they were wealthy, those who did, walked.) That he went equipped with a high degree of literacy, we know. He probably attended Perth Academy, which is some 5 miles distant from Cloag: a fine school open to boys of any social class, with a progressive curriculum which, besides the traditional ancient languages, taught contemporary subjects such as scientific navigation. Alas, the archives of Perth Academy do not go back far enough, so we know little of his schooldays. But we do have some evidence of Robert’s reading from a most curious institution, which today is little changed from when Robert visited it to borrow books.

About 15 miles from Methven lies Innerpeffray Library. This is no ordinary urban library. It lies deep in Perthshire farmland, not far from the town of Crieff. At the end of an avenue of trees stand some ancient buildings which house the oldest lending library in Scotland. There have been church buildings on the site since at least the fourteenth century, but none used as such after the Reformation. From mediaeval times the land had been in the hands of the Drummonds, another of the extensive Lowland families, but much richer and grander than the Stirlings, counting peers, an earl and later a duke among their number. David Drummond, the third Lord Maddertie, who died in 1692, had left instructions in his will that his library remain at Innerpeffray, and two years later a charity, the Innerpeffray Mortification, which is still in existence today, was established to care for the collection. Since the books were almost all to do with astrology, religion, witchcraft and demonology, this was scarcely a great contribution to human understanding, but by the standards of the time they were regarded as scholarly. Things improved with the addition of the collection of the Rev. Robert Hay Drummond half a century later, and by the time Robert Stirling was of age most of the works of scholarship and science of the later eighteenth century were available. And, astonishingly, given the period, they were available to be borrowed by local people of little or no social standing. All that was required was that the borrower sign the Borrowers’ Register, giving their name and place of residence. That Borrowers’ Register is in existence today and may be inspected on application to the librarian.

In the volume for 1806, when he was sixteen years old, the Register carries Robert’s signature and his place of residence, Cloag, to evidence his borrowing first Buffon’s Natural History (presumably not all thirty-six volumes; more likely John Leslie’s translation, for which see later), then Gibbon’s Decline and Fall and, later, Robertson’s History of America: scarcely convenient additions to the college curriculum. These works are no light literature: Robert Stirling was plainly a serious-minded young man. So, though there is little record of Robert’s early life, we know that he went up to Edinburgh University equipped with an impressive spread of information.

The Edinburgh to which Stirling travelled was an extraordinary place. At the beginning of the century it had been a narrow, strait-laced parochial town, introverted and governed by an exclusive and self-serving town council. By the century’s end it would become a society which people, not its own, would compare seriously with the Athens of Pericles or the Florence of the Medicis. The university, whose professors were paid a pittance and depended on students’ class fees for most of their income, would come to have an international reputation in philosophy, literature, history, medicine and the sciences. The great Dr Johnson, who did not love the Scots, said, ‘A man may stand at the cross of Edinburgh and shake the hand of twenty men of genius.’

In compiling a biography, the writer commonly seeks out the writings of the subject or, failing those, written evidence from his or her contemporaries. As regards scientific or technical advance, it is generally possible to trace the antecedents of the innovation through publications in scholarly journals. In Robert Stirling’s case, we have almost none of the former and little enough of the latter: with regard to both, we must rely on circumstantial evidence and proceed where possible by way of inference – for Stirling left only his sermons and his patent applications – and his great invention was perfectly unique, owing little to antecedents. That is not to say that we cannot identify some of the influences which contributed to Stirling and his works. Of those influences, easily the greatest is the milieu in which he found himself on going to Edinburgh and, later, to Glasgow. Each in its way was different from the other and each was hugely important. We will deal with the scientific background first; the ecclesiastical we shall come to later.

Edinburgh was literally extraordinary. There are few examples of small cities which, over quite a short period, have had a comparable influence on the history of human thought. Two, Athens and Florence, I have mentioned above. It’s hard to think of a fourth. Over little more than half a century, the town had gone from hosting the Jacobite Pretender and his Highland Host in a small, insanitary jumble of high-rise tenements clinging to the spine of the castle rock, to a city of planned spaces and elegant neoclassical houses. The town on the rock was still there and still insanitary, but the people who mattered in 1805 would no more have thought of hosting a rebellion against the Crown than of promoting the emancipation of Roman Catholics. Times had changed and so had the people.

That said, the city still thought of itself as a small town and it was possible for a citizen to know and be known to almost everyone of any consequence. The move to the New Town had taken most of the upper classes north to the environs of George Street, but in the lands of the High Street and the Canongate there remained enough of the old aristocracy to leaven the social mix. It was a literate and loquacious society: one in which an ability to use words, written or spoken, was the greatest social asset. It was also a society greatly given to gossip, and gossip was the main means by which news was promulgated.

A student going up to the university for the first time would get much of his information from the gossip of townspeople and his fellow students. All the professors were well known to both. Indeed, such were the eccentricities of many of the professors that they formed a constant source of interest and anecdote. And they were a pretty astonishing bunch. William Cullen and David Hume had died a generation before, but their doings were still living as legend. Hume especially, since as a reputed atheist he was at odds with the most important value systems of the time – and as a genial, friendly, witty, immensely well-informed bon viveur he was more than acceptable to everyone who cared for civilised society. As a philosopher he is today recognised as one of the greatest and the reputation which Edinburgh acquired as the Athens of the North owed something to Hume’s status vis-à-vis Plato and Aristotle. Cullen is important to our enquiry, for among his many and varied interests he included a study of heat. In 1756 he produced ice by artificial means; probably the first time this had been done.

Of the academic characters whose death clo...