8. Enlightened Science II: Progress on all fronts, The Scientists

Many accounts of the history of science describe the eighteenth century as a period when, apart from the dramatic progress in chemistry we have just described, nothing much happened. It is regarded as an interregnum, somehow in the shadow of Newton, marking time until the major advances of the nineteenth century. Such an interpretation is very wide of the mark. In fact, progress in the physical sciences in the eighteenth century proceeded on a broad front – not with any single great breakthrough to rank with the achievements of Newton, to be sure; but with a host of lesser achievements as the lessons of Newtonianism – that the world is comprehensible and can be explained in accordance with simple physical laws – were absorbed and applied. Indeed, the lesson was so widely absorbed that from now on, with a few notable exceptions,¹ it will no longer be possible to go into so much biographical detail about the scientists themselves. This is not because they become intrinsically less interesting in more recent times, but simply because there are so many of them and there is so much to describe. It is after the death of Newton that, first in the physical sciences and then in other disciplines, the story of science itself, rather than of the individuals who contributed to the story, becomes the central theme in the history of science, and it becomes harder and harder to know the dancer from the dance.

It was in the decade following the death of Newton that the term ‘physics’ started to be used, rather than ‘natural philosophy’, to describe this kind of investigation of the world. Strictly speaking, this was a revival of an old terminology, since the word had been used by Aristotle, and probably even earlier; but it marked the beginning of what we now mean by physics, and one of the first books using the term in its modern sense, Essai de physique, written by Pieter van Musschenbroek (1692–1761), was published in 1737. In the same decade, physicists started to come to grips with the mysterious phenomenon of electricity. Musschenbroek himself, who worked in Leiden, later (in the mid-1740s) invented a device that could store large quantities of electricity. It was simply a glass vessel (a jar) coated with metal on the inside and outside – an early form of what is now called a capacitor. This Leiden jar, as such devices came to be called, could be charged up, storing electricity to be used in later experiments, and if several of them were wired together they could produce a very large discharge, sufficient to kill an animal.

The study of electricity: Stephen Gray, Charles Du Fay, Benjamin Franklin and Charles Coulomb

But the first steps towards an understanding of static electricity were carried out without the aid of Leiden jars. Stephen Gray, an English experimenter (born around 1670; died in 1736) published a series of papers in the Philosophical Transactions in which he described how a cork in the end of a glass tube gained electrical characteristics (became charged, we would now say) when the glass was rubbed,² how a pine stick stuck in the cork would carry the electrical influence right to the end of the stick and how the influence could be extended for considerable distances along fine threads. Gray and his contemporaries made their electricity as and when they needed it, by friction, from simple machines in which a globe of sulphur was rotated while being rubbed (later, glass spheres or cylinders were substituted for the sulphur). Partly influenced by Gray’s work, the Frenchman Charles Du Fay (1698–1739) discovered in the mid-1730s that there are two kinds of electricity (what we now call positive and negative charge) and that similar kinds repel one another while opposite kinds attract. Between them, the work of Gray and Du Fay also demonstrated the importance of insulating material in preventing electricity draining away from charged objects, and showed that anything could be charged with electricity if it was insulated – Du Fay even electrified a man suspended by insulating silk cords and was able to draw sparks from the body of his subject. As a result of his work, Du Fay came up with a model of electricity which described it in terms of two different fluids.

This model was refuted by the model developed by Benjamin Franklin (1706–1790), whose interest in electricity extended far beyond the famous, and hazardous, kite experiment (which was, incidentally, carried out in 1752 to charge up a Leiden jar and thereby prove the connection between lightning and electricity). In spite of all his other interests and activities, Franklin found time, from the mid–1740s into the early 1750s, to carry out important experiments (making use of the recently invented Leiden jars) which led him to a one-fluid model of electricity based on the idea that a physical transfer of the single fluid occurred when an object became electrically charged, leaving one surface with ‘negative’ charge and one with ‘positive’ charge (terms that he introduced). This led him naturally to the idea that charge is conserved – there is always the same amount of electricity, but it can be moved around, and overall the amount of negative charge must balance the amount of positive charge. Franklin also showed that electricity can magnetize and demagnetize iron needles, echoing work carried out a little earlier by John Michell (1724–1793), Henry Cavendish’s friend who devised the ‘Cavendish experiment’. By 1750, Michell had also discovered that the force of repulsion between two like magnetic poles obeys an inverse square law, but although he published all these results that year in A Treatise on Artificial Magnets, nobody took much notice, just as nobody took much notice of the various contributions of Franklin, Priestley and Cavendish in determining that the electric force obeys an inverse square law. It was not until 1780 that Charles Coulomb (1736–1806), building on the work of Priestley, carried out the definitive experiments on both electric and magnetic forces, using a torsion balance, which finally convinced everyone that both forces obey an inverse square law. This has therefore gone down in history as Coulomb’s law.

Once again, these examples highlight the interplay between science and technology. The study of electricity only began to gather momentum after machines that could manufacture electricity were available, and then when devices to store electricity were developed. The inverse square law itself was only developed through the aid of the technology of the torsion balance. But the biggest technological breakthrough in the eighteenth-century study of electricity came right at the end of the century, paving the way for the work of Michael Faraday and James Clerk Maxwell in the nineteenth century. It was the invention of the electrical battery, and it resulted from an accidental scientific discovery.

The discovery was made by Luigi Galvani (1737–1798), a lecturer in anatomy and professor of obstetrics at the University of Bologna. Galvani carried out a long series of experiments on animal electricity, which he described in a paper published in 1791. In it, he recounted how he had first become interested in the subject after noticing twitching in the muscle of a frog laid out for dissection on a table where there was also an electrical machine. Galvani showed that the twitching could be induced by connecting the muscles of the dead frog directly to such a machine or if the frog were laid out on a metal surface during a thunderstorm. But his key observation came when he noticed that frogs’ legs being hung out to dry twitched when the brass hook they were suspended on came into contact with an iron fence. Repeating this experiment indoors, with no outside source of electricity around, he concluded that the convulsions were caused by electricity stored, or manufactured, in the muscles of the frog.

Not everyone agreed with him. In particular, Alessandro Volta (1745–1827), the professor of experimental physics at Pavia University, in Lombardy, argued in papers published in 1792 and 1793 that electricity was the stimulus for the contraction of the muscles, but that it came from an outside source – in this case, from an interaction between the two metals (brass and iron) coming into contact. The difficulty was proving it. But Volta was a first-class experimenter who had already carried out important work on electricity (including the design of a better frictional machine to make static electricity and a device to measure electric charge) and had also worked on gases, measuring the amount of oxygen in the air by exploding it with hydrogen. He was well able to rise to this new challenge.

Volta first tested his ideas by placing different pairs of metals in contact and touching them with his tongue, which proved sensitive to tiny electrical currents that could not be detected by any of the instruments available at the time. While he was carrying out these experiments and trying to find a way to magnify the effect he could feel with his tongue into something more dramatic, his work was hampered by the political upheavals that affected Lombardy as a result of the French Revolution and subsequent conflict between France and Austria for control of the region. But by 1799 Volta had come up with the device that would do the trick. He described it in a letter to Joseph Banks, then President of the Royal Society, which was read to a meeting of the Royal in 1800.

His key invention was literally a pile of silver and zinc discs, alternating with one another and separated by cardboard discs soaked in brine. Known as a Voltaic pile, this was the forerunner of the modern battery, and produced a flow of electric current when the top and bottom of the pile were connected by a wire. The battery provided, for the first time, a more or less steady flow of electric current, unlike the Leiden jar, which was an all or nothing device that discharged its store of electricity in one go. Before Volta’s invention, the study of electricity was essentially confined to the investigation of static electricity; after 1800, physicists could work with electric currents, which they could turn on and off at will. They could also strengthen the current by adding more discs to the pile, or reduce it by taking discs away. Almost immediately, other researchers found that the electric current from such a pile could be used to decompose water into hydrogen and oxygen, the first hint of what a powerful tool for science the invention would become. Although we shall have to wait until Chapter 11 to follow up the implications, the importance of Volta’s work was obvious immediately, and after the French won control of Lombardy in 1800, Napoleon made Volta a Count.

If it took some time for physicists to come to grips with electricity, many of their ideas from the eighteenth century seem surprisingly modern, even if they were not always fully developed or widely appreciated at the time. For example, it was as early as 1738 that the Dutch-born mathematician Daniel Bernoulli (1700–1782) published a book on hydrodynamics which described the behaviour of liquids and gases in terms of the impact of atoms on the walls of their container – very similar to the kinetic theory of gases developed more fully in the nineteenth century and, of course, very much a development of the ideas of Newton concerning the laws of motion. Such ideas were also spreading geographically. In 1743, just five years after Bernoulli published his great book, we find Benjamin Franklin among the leading lights in establishing the American Philosophical Society in Philadelphia – the first scientific society in what is now the United States and the tiny seed of what would become a great flowering of science in the second half of the twentieth century.

One of the most important insights in the whole of science, whose value only really became apparent during that twentieth century flowering, was formulated by Pierre-Louis de Maupertuis (1698–1759) just a year later, in 1744. De Maupertuis had been a soldier before turning to science; his big idea is known as the principle of least action. ‘Action’ is the name given by physicists to a property of a body which is measured in terms of the changing position of an object and its momentum (that is, it relates mass, velocity and distance travelled by a particle). The principle of least action says that nature always operates to keep this quantity to a minimum (in other words, nature is lazy). This turned out to be hugely important in quantum mechanics, but the simplest example of the principle of least action at work is that light always travels in straight lines.

Speaking of light, in 1746 Leonhard Euler (1707–1783), a Swiss regarded as the most prolific mathematician of all time, and the man who introduced the use of the letters e and i in their modern mathematical context, described mathematically the refraction of light, by assuming (following Huygens) that light is a wave, with each colour corresponding to a different wavelength; but this anti-Newtonian model did not take hold at the time.³ The wave model of light languished because Newton was regarded in such awe; other ideas languished because they came from obscure scientists in remote parts of the world. A classic example is provided by Mikhail Vasil’evich Lomonosov (1711–1765), a Russian polymath who developed the Newtonian ideas of atoms, came up with a kinetic theory similar to that of Bernoulli and, around 1748, formulated the laws of conservation of mass and energy. But his work was virtually unknown outside Russia until long after his death.

There were also ideas that were ahead of their time in astronomy. The Durham astronomer Thomas Wright (1711–1786) published (in 1750) An Original Theory and new Hypothesis of the Universe, in which he explained the appearance of the Milky Way by suggesting that the Sun is part of a disc of stars which he likened to a mill wheel. This was the same Wright whose ‘day job’ as a surveyor brought him into contact with Charles and Henry Cavendish. In 1781, William (1738–1822) and Caroline (1750–1848) Herschel discovered the planet Uranus, a sensation at the time as the first planet that had not been known to the Ancients, but barely hinting at the discoveries to be made beyond the old boundaries of the Solar System. And Henry Cavendish’s good friend John Michell (1724–1793) was, as is now well known, the first person to come up with the idea of what are now known as black holes, in a paper read to the Royal Society on Michell’s behalf by Cavendish in 1783.⁴ Michell’s idea was simply based on the (by then well-established) fact that light has a finite speed and the understanding that the more massive an object is, the faster you have to move to escape from its gravitational grip. It’s worth quoting from that paper, if only for the pleasure of imagining the otherwise shy Henry Cavendish in his element, reading it out to the packed throng at the Royal:

If there should really exist in nature any bodies whose density is not less than that of the sun, and whose diameters are more than 500 times the diameter of the sun, since their light could not arrive at us…we could have no information from sight; yet, if any other luminiferous bodies should happen to revolve around them we might still perhaps from the motions of these revolving bodies infer the existence of the central ones.

Indeed, that is just how astronomers infer the existence of black holes today – by studying the motion of bright material in orbit around the black hole.

It’s surprising enough that one person came up with the idea of black holes (which we are used to thinking of as a quintessential example of twentieth-century theorizing) before the end of the eighteenth century – even more surprising that a second person independently came up with the same idea before the century closed. That person was Pierre Simon Laplace, and it’s worth slowing down the pace of our story to take stock of where physics stood at the end of the eighteenth century by taking a slightly more leisurely look at the career of the man sometimes referred to as ‘the French Newton’.

Laplace was born at Beaumont-en-Auge, near Caen, in the Calvados region of Normandy, on 28 March 1749. Little is known of his early life – indeed, not much is known about his private life at all. Some accounts refer to him coming from a poor farming family, but although his parents were not rich, they were certainly comfortably off. His father, also Pierre, was in the cider business, if not in a big way, and also served as a local magistrate, giving a clear indication of his status in the community. His mother, Marie-Anne, came from a family of well-off farmers at Tourgéville. Just as Laplace was named after his father, so his only sibling, a sister born in 1745, was named Marie-Anne, after her mother. Laplace went to school as a day boy at a local college run by the Benedictines, and was probably intended by his father for the priesthood. From 1766 to 1768 he studied at the University of Caen, and it seems to have been at this time that he was found to have a talent for mathematics. He helped to support himself at college by working as a private tutor, and there is some evidence that he briefly worked in this capacity for the Marquis d’Héricy, who was to play such an important part in Georges Couvier’s life. Laplace left Caen without taking a degree and went to Paris with a letter from one of his professors recommending him to Jean d’Alembert (1717–1783), one of the top mathematicians in France at the time and a high-ranking member of the Academy. D’Alembert was sufficiently impressed by the young man’s abilities that he found him a post with the grand title of professor of mathematics at the École Militaire, but which really just consisted of trying to drum the basics of the subject into reluctant officer cadets. He stayed in the post from 1769 to 1776, making a reputation for himself with a series of mathematical papers (as ever with the maths, we won’t go into the details here) and being elected to the Academy in 1773.

Laplace was particularly interested in probability, and it was through this mathematical interest that he was led to investigate problems in the Solar System, such as the detailed nature of the orbits of the planets and of the Moon around the Earth. Could these have arisen by chance? Or must there be some physical reason why they have the properties they do? One example, which Laplace discussed in 1776, concerns the nature and orbits of comets. All the planets move around the Sun in the same direction and in the same plane (the plane of the ecliptic). This is a powerful indication (we shall soon see how powerful) that they all formed together by the same physical process. But comets orbit the Sun in all directions and at all angles (at least judging from the evidence of the few dozen comets whose orbits were known at the time). This suggests that they have a different origin, and mathematicians before Laplace had already reached this conclusion. But as a mathematician, Laplace was not so much concerned with the conclusion but with how it had been arrived at; he developed a more sophisticated analysis which showed probabilistically that it was highly unlikely that some force existed that was trying to make comets move in the plane of the ecliptic. In the mid-1770s, Laplace also looked for the first time at the behaviour of the orbits of Jupiter and Saturn.⁵ These orbits showed a slight, long-term shift which did not seem to fit the predictions of Newtonian gravitational theory, and Newton himself had suggested that after a long enough time (only a few hundred years!) divine intervention would be required to put the planets back in their proper orbits and prevent the Solar System falling apart. Laplace’s first stab at the puzzle didn’t find the answer, but returning to the problem in the 1780s, he showed conclusively that these secular variations, as they are called, can be explained within the framework of Newtonian theory and are caused by the disturbing influences of the two planets on one another. The variations follow a cycle 929 years long, which brings everything back to where it started, so the Solar System is stable after all (at least on all but the longest timescales). According to legend, when asked by Napoleon why God did not appear in his discussion of the secular variations, he replied, ‘I have no need of that hypothesis.’

Laplace also worked on the theory of tides, explaining why the two tides each day reach roughly the same height (more naive calculations ‘predicted’ that one high tide should be much higher than the other), developed his ideas on probability to deal with practical problems such as estimating the total population of France from a sample of birth statistics and, as we have seen, worked with Lavoisier (almost six years older than Laplace and then at the height of his reputation) on the study of heat. It is an interesting insight into the state of science in the 1780s that although Lavoisier and Laplace, undoubtedly two of the greatest scientists of the time, discussed their experimental results both in terms of the old caloric model of heat (more of this shortly) and the new kinetic theory, they carefully avoided choosing between them, and even suggested that both might be at work at the same time.

In 1788, we get a chink of an insight into Laplace’s private life. On 15 May, by now well established as a leading member of the Academy, he married Marie-Charlotte de Courty de Romanges. They had two children. A son, Charles-Emile, was born in 1789, became a general and died (childless) in 1874; a daughter, Sophie-Suzanne, died giving birth to her own daughter (who survived) in 1813. It was around the time of his marriage that Laplace made his definitive study of planetary motions. As well as explaining the secular variations of the orbits of Jupiter and Saturn, he solved a long-standing puzzle about similar changes in the orbit of the Moon around the Earth, showing that they are produced by a complicated interaction between the Sun and the Earth–Moon system and the gravitational influence of the other planets on the Earth’s orbit. In April 1788, he was able to state (using the word ‘world’ where we would say ‘Solar System’):

The system of the world only oscillates around a mean state from which it never departs except by a very small quantity. By virtue of its constitution and the law of gravity, it enjoys a stability that can be destroyed only by foreign causes, and we are certain that their action is undetectable from the time of the most ancient observations until our own day.⁶

Although we know little about his private life, Laplace was clearly a great survivor, and one reason why we know so little is that he never openly criticized any government or got involved in politics. He survived the various forms of government following the French Revolution, most of which were eager to be associated with him as a symbol of French prestige. At the only time when he might have been at risk, during the Terror, Laplace had already seen which way the wind was blowing and had prudently removed himself and his family to Melun, some 50 kms southeast of Paris. There he kept his head down until after the fall of the Jacobins, when he was called back to Paris to work on the reorganization of science under the Directory.

Laplace had already worked on the metric system before the Jacobin interlude; now, his work on reforming the educational system of France to include proper teaching of science led him to write one of the most influential books about science ever published, the Exposition du système du monde, which appeared in two volumes in 1796. Laplace’s prestige and his ability to bend with the wind saw him serve in government under Napoleon, who made him a Count in 1806, but remain in favour with the restored monarchy, with Louis XVIII making him the Marquis de Laplace in 1817. But in spite of continuing to work in mathematics and all the honours heaped on him in his long life (he died in Paris on 5 March 1827), in terms of the development of science, the Exposition remains Laplace’s most important achievement, still valuable today as a summing up of where physics stood at the end of the eighteenth century. And it was appreciated as such at the time – on the flyleaf of a copy given to the College of New Jersey (now Princeton University) in 1798, the donor has written:

This treatise, considering its object and extent, unites (in a much higher degree than any other work on the same subject that we ever saw) clearness, order and accuracy. It is familiar without being vague; it is precise but not abstruse; its matter seems drawn from a vast stock deposited in the mind of the author; and this matter is impregnated with the true spirit of philosophy.⁷

The fundamental basis of that philosophy was spelled out by Laplace himself in his great book, and, if anything, rings more true today than at any time in the past two centuries:

The simplicity of nature is not to be measured by that of our conceptions. Infinitely varied in its effects, nature is simple only in its causes, and its economy consists in producing a great number of phenomena, often very complicated, by means of a small number of general laws.

There speaks the voice of experience, from the man who explained the complexities of the Solar System in terms of Newton’s simple law of gravity.

Laplace’s summing up of physics ranges from planetary astronomy, orbital motion and gravity through mechanics and hydrostatics, and right at the end he introduces a couple of new (or newish) ideas. One of these is the so-called ‘nebular hypothesis’ for the origin of the Solar System, which was also thought up by Immanuel Kant (1724–1804) in 1755, although there is no indication that Laplace knew about Kant’s then rather obscure work. This is the idea that the planets formed from a cloud of material around the young Sun, shrinking down into a plane as the cloud, or nebula, contracted. At the time, there were seven known planets and fourteen satellites all orbiting the Sun in the same direction. Eight of these systems were also known to be rotating on their axes in the same sense that they were orbiting around the Sun – if you look down on the North pole of the Earth, for example, you see the Earth rotating anticlockwise on its axis, while the planet is moving anticlockwise around the Sun. Laplace calculated that, since there is a 1 in 2 chance of each orbit or rotation being ‘forward’ rather than ‘backward’, the total odds against this happening by chance were (1 – (1/2)²⁹), a number so close to 1 that it was certain that these bodies had formed together, and the nebular hypothesis seemed the best way to account for this. It is, indeed, the model still favoured today.

The other new idea was, of course, Laplace’s version of black holes. Intriguingly, this discussion (which was along very similar lines to that of Michell, but much more brief) appeared only in the first edition of the Exposition; but there is no record of why Laplace removed it from the later editions. His version of the hypothesis of dark stars pointed out that a body with a diameter 250 times that of the Sun and with the same density as the Earth would have such a strong gravitational attraction that even light could not escape from it.⁸ In truth, this is merely a historical curiosity, and the speculation had no influence on the development of science in the nineteenth century. But the book as a whole did, not only for its content but for its clarity and easy style, which is typified by the opening sentences with which Laplace sucks his readers in:

If on a clear night, and in a place where the whole horizon is in view, you follow the spectacle of the heavens, you will see it changing at every moment. The stars rise or set. Some begin to show themselves in the east, others disappear in the west. Several, such as the Pole Star and the Great Bear, never touch the horizon in our climate…

Laplace’s story is almost all science and very little personality, although some of this does seem to shine through in the Exposition. But don’t run away with the idea that by the late eighteenth century physics (let alone the rest of science) had settled down into some kind of dull routine. There were still plenty of ‘characters’ around, and of all the eighteenth-century physicists, the most colourful career was that of Benjamin Thompson (later Count Rumford). He made important contributions to science, particularly in the study of heat, and no less important contributions as a social reformer, although these were not motivated by politics but by practicality. Indeed, Thompson seems to have been an opportunist largely motivated by self-interest, and it is rather ironic that the best way he found to promote his own wealth and status turned out to be to do good for others. But since his career gives a sideways look at both the American Revolution and the upheavals in Europe at the end of the eighteenth century (as well as being an entertaining story in its own right) it’s worth going into in a little more detail than his purely scientific contribution really justifies.

Thompson was born on 26 March 1753, the son of a farmer in Woburn, Massachusetts. His father died not long after he was born, and his mother soon remarried and had several more children. Although Benjamin was an inquisitive and intelligent boy, the family were poor and his position offered no chance of anything other than the most rudimentary education. From the age of 13, he had to work to help to support the large family, first as a clerk to an importer of dry goods in the port of Salem, and later (from October 1769) as a shop assistant in Boston. Part of the appeal of Boston was that it offered an opportunity for the young man to attend evening classes, and it was also a hotbed of political unrest, which carried its own excitement for a teenager; but he neglected his job (which bored him rigid) and soon lost it – one story has it that he was fired, another that he left voluntarily. Either way, he spent most of 1770 back home in Woburn, unemployed, dividing his time between the usual teenage interests and attempting self-education with help from a slightly older friend, Loammi Baldwin. Partly through his charm, and partly because he was clearly interested in what was then still (in that part of the world) known as natural philosophy, the local physician, a Dr John Hay, agreed to take Thompson on as his apprentice, and he used the opportunity to combine a personal programme of study with his duties – he even seems to have attended a few lectures at Harvard, although he had no official connection with the university (however, since this is based only on Thompson’s own account, it should, as we shall see, be taken with a pinch of salt).

The trouble with being an apprentice was that it cost money, and in order to pay his way, Thompson took on a variety of part-time teaching jobs – since all that he was expected to teach was reading, writing and a little reckoning, he needed no formal qualifications for this. By the summer of 1792, either Thompson had had enough of being an apprentice or the doctor had had enough of him, and he decided to try his hand at full-time schoolmastering. He found a post in the town of Concord, New Hampshire. The town actually lay right on the border of Massachusetts and New Hampshire, and had previously been known as Rumford, Massachusetts; the name was changed at the end of 1762 as a conciliatory gesture after a bitter wrangle about which state the town belonged in and who it should be paying taxes to. Thompson’s patron in Concord was the Reverend Timothy Walker. Walker’s daughter, Sarah, had recently married (at the rather advanced age of 30) the richest man in town, Benjamin Rolfe, who had promptly died at the age of 60, leaving her very well off. Schoolmastering lasted an even shorter time than any of Thompson’s other jobs to date, and in November 1772 he married Sarah Walker Rolfe and settled down to manage his wife’s estate and turn himself into a gentleman. He was still only 19, tall and good-looking, and always said that it had been Sarah who made the running in their relationship. They had one child, Sarah, born on 18 October 1774. But by then, Thompson’s life had already begun to take another twist.

The trouble with Thompson was that he was never satisfied with what he had got and always wanted more (at least, right up until the last months of his life). Thompson lost no time in ingratiating himself with the local governor, John Wentworth. He proposed a scientific expedition to survey in the nearby White Mountains (although these plans came to nothing) and commenced a programme of scientific agriculture. But all this was against the background of the turmoil leading up to the American Revolution. Although this is no place to go into the details, it’s worth remembering that in its early stages this was very much a dispute between two schools of thought which both regarded themselves as loyal English. Thompson threw in his lot with the ruling authorities, and it is in this connection that his otherwise surprising appointment as a major in the New Hampshire militia occurred in 1773, only a few months after his marriage. In preparation for the fighting that most people knew was inevitable, the colonials (for want of a better term) were encouraging (indeed, bribing) deserters from the British army to join the ranks and train them in organized warfare; Major Thompson, as a landowner with many contacts among the farmers of the region, was in an ideal position to keep an eye on this activity. Since Thompson was also quite outspoken in his belief that true patriotism meant obeying the rule of law and working within the law to make changes, it didn’t take too long for those plotting the overthrow of the old regime to become aware of his activities. Shortly before Christmas 1774, just a couple of months after the birth of his daughter, hearing that a mob was gathering with the objective of tarring and feathering him, Thompson headed out of town on horseback never to return. He never saw his wife again, although, as we shall see, his daughter Sarah did eventually re-enter his life.

Thompson now headed for Boston, where he offered his services to the governor of Massachusetts, General Thomas Gage. Officially, these were rejected and Thompson returned to Woburn. In fact, he had now become a spy for the British authorities, passing back information about rebel activities to the headquarters in Boston. Before very long his position in Woburn also became untenable, and in October 1775 he rejoined the British in Boston. When they were thrown out by the rebels in March 1776, most of the garrison and loyalists sailed for Halifax, Nova Scotia, while the official dispatches from Boston bearing the unwelcome news of this setback for the British forces were sent to London in the care of Judge William Brown. Somehow, Major Benjamin Thompson managed to wangle a place in Judge Brown’s entourage, and he arrived in London in the summer of 1776 as an expert with first-hand information about the fighting abilities of the American rebels and as an eye-witness to the fall of Boston from the American side. Furthermore, he presented himself as a gentleman who had lost his large estates through his loyalty to the British cause. With these credentials and his own impressive organizational ability, he quickly became the right-hand man of Lord George Germain, the Secretary of State for the Colonies.

Thompson was good at his job and very successful, becoming, by 1780, Under-secretary of State for the Northern Department. But his work as a civil servant lies outside the scope of this book. Alongside that work, however, he also returned to scientific interests, and in the late 1770s he carried out experiments to measure the explosive force of gunpowder (obviously both topical and relevant to his day job), which led to him being elected as a Fellow of the Royal Society in 1779. These experiments also provided the excuse for Thompson to spend three months on manoeuvres with part of the British Navy in the summer of 1779; but although ostensibly studying gunnery, in fact Thompson was once again working as a spy, this time for Lord Germain, reporting back incredible (but true) tales of inefficiency and corruption in the Navy which Germain could use to further his own political career. Thompson was well aware, though, that under the system of patronage that existed at the time, his star was firmly tied to Germain’s and if his patron fell from favour he would be out in the cold. So he set about preparing a fall-back position for himself.

This involved a standard ploy for someone of his rank – forming his own regiment. In order to boost the strength of the army at times of need, the King could issue a Royal Charter which allowed an individual to raise a regiment at his own expense and to become a senior officer in that regiment. It was an expensive process (although Thompson could by now afford it), but carried a huge bonus – at the end of hostilities, when the regiment disbanded, the officers kept both their rank and an entitlement to half-pay for life. So Thompson became a lieutenant-colonel in the King’s American Dragoons, which were actually recruited in New York for Thompson by a Major David Murray. In 1781, though, Thompson’s pretend soldiering suddenly became real. A French spy was caught with details of British naval operations and his information clearly came from someone in high office with detailed knowledge of the fleet. Thompson was suspected and there was much gossip, but no charges were laid. We shall never know the truth, but it is a fact that he abruptly gave up his position in London and headed for New York to take an active part with his regiment. Thompson’s role in the fighting was neither glorious nor successful, and in 1783, after the defeat of the British, he was back in London, where his friends were still influential enough to arrange for him to be promoted to full colonel, thereby considerably boosting his income, before being retired on half-pay. Just after his promotion, he had his portrait, in full uniform, painted by Thomas Gainsborough.

Colonel Thompson, as he now was, decided next to try his fortune on the mainland of Europe, and after a few months touring the continent sizing up possibilities, with a combination of charm, luck and rather exaggerated stories of his military service, he was offered a post as military aide in Munich by the Elector of Bavaria, Carl Theodor. At least he was almost offered a post. It was intimated that in order to avoid offending other members of the Bavarian court, it would be helpful if Thompson could be seen to be well in with the British King, George III. In any case, as a colonel in the British army, he would have to return to London to obtain permission to serve a foreign power. While he was there, Thompson persuaded the King that it would be helpful if he received a knighthood, and the favour was duly granted. Thompson almost always got what he wanted, but this impressive piece of cheek owed much of its success to the fact that Britain was keenly interested in improving relations with Bavaria in view of the way the political situation was now (in 1784) developing in France. It’s also clear, and hardly surprising, given his track record, that Sir Benjamin offered to spy on the Bavarians for the British, reporting secretly to Sir Robert Keith, the British Ambassador in Vienna.

Thompson was a phenomenal success in Bavaria, where he applied scientific principles to turning a poorly equipped army with low morale, barely more than a rabble, into an efficient, happy machine (although not a fighting machine). His job, seemingly impossible, was to achieve this while saving the Elector money, and he did so by the application of science. The soldiers needed uniforms, so Thompson studied the way heat was transmitted by different kinds of material to find the most cost-effective option for their clothing. Along the way, he accidentally discovered convection currents,⁹ when he noticed the liquid (alcohol) in a large thermometer being used in his experiments rising up the middle of the tube and falling down the sides. The soldiers also needed feeding, so he studied nutrition and worked out how to feed them economically but healthily. In order to make the uniforms, he swept the streets of Munich clear of beggars, and put them to work in (by the standards of the day) well-equipped, clean workshops, where they were also offered the rudiments of education, and where the younger children were obliged to attend a form of school. To provide maximum nutrition for the troops at minimum cost, he fed them on (among other things) his nutritious soup – based on the potato, a vegetable scarcely used in that part of Europe at the time – which required every barracks to have a kitchen garden and grow its own vegetables. This provided useful work and skills that the soldiers would be able to employ when they left the army, and did much to raise morale. In Munich itself, the military vegetable garden was incorporated into a grand public park, which became known as the English Garden, carved out of what had been the Elector’s private deer park, which helped to make Thompson very popular with the populace.

Among his many inventions, Thompson designed the first enclosed kitchen ranges, replacing inefficient open fires; portable stoves for use in the field; improved lamps; and (later) efficient coffee pots (a lifelong teetotaller who hated tea, Thompson was eager to promote coffee as a healthy alternative to alcohol). His official position at court made him the most powerful man in Bavaria after the Elector, and before too long he held (simultaneously) the posts of Minister of War, Minister of Police, State Councillor and Chamberlain to the Court, and the rank of major-general. In 1792, the Elector found another way to honour his most trusted aide. At that time, the last vestiges of the Holy Roman Empire still existed, as a very loose coalition of states of central Europe and with an ‘Emperor’ whose role was no more than ceremonial. That year, the Emperor Leopold II died, and while the various crowned heads were assembling to select a successor, Carl Theodor became, under the system of Buggins’ turn operating at the time, caretaker Holy Roman Emperor. He held the post from 1 March to 14 July 1792, long enough to ennoble a few of his favourites, including Major-General Sir Benjamin Thompson, who became Count Rumford (in German, Graf von Rumford, an unlikely title for an American-English scientist).¹⁰

Although, as this example indicates, Rumford (as we shall now refer to him) was still very much the Elector’s blue-eyed boy, his position as a foreigner who had risen so far so soon earned him many enemies at court. Carl Theodor was old and childless, and there was already jockeying for position among the factions for when the inevitable happened. Rumford had achieved so much that there seemed little more scope for him to move further up the social ladder. He was now 39, and his thoughts were turning to the possibility of returning to America, when he received, out of the blue, a letter from his daughter Sarah, usually known as Sally. Rumford’s wife had just died and Sally had been given his address by Loammi Baldwin.

When the French invaded the Rhineland and took over Belgium in November 1792, with war threatening to engulf Bavaria, Rumford, who was genuinely exhausted, had had enough and left for Italy, officially on grounds of ill health, although with an element of political expediency. The Italian sojourn was part holiday, partly an opportunity to revive his interests in science (he saw Volta demonstrate the way frogs’ legs twitched under the influence of electricity and met up with Sir Charles Blagden, Secretary of the Royal Society and friend of Henry Cavendish), partly an opportunity for romantic dalliance (Rumford was never short of female companionship; he had several mistresses, including two sisters, each a Countess, one of whom he ‘shared’ with the Elector, and he fathered at least two illegitimate children).

Rumford spent sixteen months in Italy, but did return to Bavaria in the summer of 1794, now with an ambition to make a name for himself in science – he was no Henry Cavendish, content with the discoveries for themselves without seeking public acclaim. The political situation was still the same, and in any case for Rumford’s work to be noticed it would have to be published in England, preferably by the Royal Society. In the autumn of 1795, the Elector granted him a six-months leave of absence to travel to London for this purpose. There, now famous as a scientist and statesman, and with a noble title to boot, Rumford was in his element and stretched the six months out to almost a year. As ever, he combined business, self-promotion, science and pleasure. Shocked by the pall of smoke which hung over London in winter, he used his understanding of convection to design a better fireplace, with a ledge or shelf at the back of the chimney so that cold air falling down the chimney struck this ledge and was deflected to join the hot air rising from the fire without sending clouds of billowing smoke into the room (he later worked on central heating systems, using steam). In 1796, partly out of egotism, to perpetuate his own name (but, to be fair, using his own money) Rumford endowed two prize medals to be awarded for outstanding work in the fields of heat and light, one for America and one for Britain. The same year, he brought Sally over from America to join him, and although he was initially shocked by her colonial country-bumpkin ways, a social embarrassment to the sophisticated Count Rumford, they spent much time together over the rest of his life.

Rumford was called back to Munich in August 1796, partly because the political situation had changed in his favour (the latest heir presumptive to Carl Theodor was a supporter of Rumford) and partly because of military threats to Bavaria (indeed, to Munich itself), which seemed set to be caught between opposing Austrian and French armies.¹¹ It wasn’t so much that Rumford was genuinely thought to be a great military leader, but more that he was a convenient scapegoat – just about everybody of importance fled Munich, leaving the foreigner as Town Commandant, meaning that he would carry the can when the city was invaded. Soon, the Austrians arrived and set up camp on one side of the town. Then the French arrived and set up camp on the other side of the town. Each army was determined to occupy Munich rather than let their opponents have it, but Rumford, shuttling between the camps and playing for time, managed to avoid triggering any conflict until the French were pulled out following the defeat of another of their armies on the lower Rhine. Rumford came out of it all smelling of roses, as ever. When the Elector returned, as a reward he appointed Rumford as Commandant of the Bavarian police, and made Sally, who had accompanied her father, a Countess in her own right, although no extra income resulted from this and the pension Rumford was entitled to as a Count was to be divided equally between the two of them. He was also promoted to general.

The unexpected success, however, made Rumford even more unpopular with the opposition and he became eager to move on, neglecting his administrative duties and carrying out his most important scientific work around this time. Even the Elector realized that he was weakening his own position by continuing to favour Rumford – but what could he do with him? A face-saving resolution to the problem seemed to have been found in 1798, when Carl Theodor appointed Count Rumford Minister Plenipotentiary to the Court of St James (that is, Ambassador to Britain). Rumford packed up his belongings and headed back to London, only to discover that George III had no intention whatever of accepting his credentials, using the excuse that as a British national he could not represent a foreign government, but probably actually because George III’s ministers disliked Rumford, regarded him as an upstart and had long memories of his previous double-dealings in the spying trade.

Whatever the reason, the effect turned out well for science. Rumford considered, once again, returning to America, but in the end stayed in London and came up with a scheme to establish a combined museum (giving prominence to his own work, of course), research and educational establishment, which came to fruition as the Royal Institution (RI). Raising the necessary money through public subscription (that is, persuading the rich, with his usual charm, to dig deep into their pockets), he saw the RI open its doors in 1800, with a series of lectures by Thomas Garnett, a physician, lately from Glasgow, who was given the title professor of natural philosophy at the RI. But Garnett did not last long in the job – Rumford was unimpressed by his abilities and in 1801 replaced him with a rising young man, Humphry Davy, who was to make the RI a huge success in promoting the public understanding of science.

Soon after appointing Davy, Rumford went back to Munich to pay his respects to the new Elector, Maximilian Joseph, who had recently succeeded Carl Theodor. He was, after all, still being paid by the Bavarian government and Maximilian had expressed an interest in establishing a similar institution to the RI in Munich. After a couple of weeks there, Rumford set off back to London via Paris, where he was greeted with all the acclaim that he thought he deserved and, fatefully, made the acquaintance of the widow Lavoisier, now in her early forties (Rumford, of course was now in his late forties).¹² After all this, London palled. Rumford sorted out his affairs, packed up and left permanently for the Continent on 9 May 1802. There were other visits to Munich, but these ended in 1805, when Austria took over the territory and the Elector fled. Rumford had had the foresight to wind up his affairs there before the storm broke; his heart was now in Paris with Madame Lavoisier. She joined him on an extended tour of Bavaria and Switzerland, and in the spring of 1804 the couple had settled in a house in Paris. They decided to marry, but ran into the technical difficulty that Rumford had to obtain papers from America proving that his first wife was dead; not so easy with war raging and France blockaded by the British. This delayed things until 24 October 1805, when they finally did marry and almost immediately (after some four years of pre-marital bliss together!) found that they were incompatible. Rumford was ready for a quiet life of semi-retirement and science; his wife wanted parties and a full social life. They parted after a couple of years, and Rumford spent his last years at a house on the outskirts of Paris, in Auteuil, consoled by another mistress, Victoire Lefèvre. They had a son, Charles, who was born in October 1813, less than a year before Rumford died on 21 August 1814, at the age of 61. Sally Rumford lived until 1852, but never married, and left a substantial bequest to Charles Lefèvre’s son, Amédé, on condition that he changed his name to Rumford. His descendants still carry that name.

Fascinating though the story of Benjamin Thompson/Count Rumford is (and I have only scratched the surface of it here), it would have no place in a history of science if Rumford had not made one really important contribution to our understanding of the nature of heat. This came about through his work in Munich in 1797, where, following his ‘defence’ of the city, among his many responsibilities he was in charge of the Munich Arsenal, where cannon were made by boring out metal cylinders. Rumford was throughout his life an intensely practical man, an inventor and engineer more in the mould of a James Watt than a theorist like Newton, and his main scientific interest concerned the nature of heat, which was still very much a puzzle in the second half of the eighteenth century. The model which still held sway in many quarters was the idea that heat was associated with a fluid called caloric. Every body was thought to possess caloric, and when caloric flowed out of a body it made its presence known by raising the temperature.

Rumford became interested in the caloric model while he was carrying out his experiments with gunpowder in the late 1770s. He noticed that the barrel of a cannon became hotter if it was fired without a cannon ball being loaded than it did when there was a cannon ball being fired, even though the same amount of gunpowder was used. If the rise in temperature was simply due to the release of caloric, then it should always be the same if the same amount of powder was burnt, so there must be something wrong with the caloric model.¹³ There were rival models. As a young man, Rumford had read the work of Herman Boerhaave (1668–1738), a Dutchman best remembered for his work in chemistry, in which he suggested that heat was a form of vibration, like sound. Rumford found this model more appealing, but it wasn’t until he became involved in cannon-boring almost twenty years later that he found a way to convince people of the deficiencies of the caloric model.

It was, of course, very easy for the caloric model to explain, superficially, the familiar fact that friction produces heat – according to this model, the pressure of two surfaces rubbing together squeezes caloric out of them. In the cannon-boring process, the metal cylinders were mounted horizontally against a non-rotating drill bit. The whole cylinder was rotated (literally, by horsepower) and the drill moved down the cannon as the boring proceeded. When Rumford observed this process, he was impressed by two facts. First, the sheer quantity of heat generated, and second, that the source of this heat seemed to be inexhaustible. As long as the horses kept working and the drill bit was in contact with the metal of the cannon, heat could be generated. If the caloric model were correct, then surely at some point all the caloric would have been squeezed from the rotating cylinder and there would be none left to make it hot.

Rumford made an analogy with a sponge, soaked in water and hung from a thread in the middle of a room. It would gradually give up its moisture to the air, and eventually become dry and free from moisture. That would be equivalent to the caloric model. But heat was more like the ringing of a church bell. The sound produced by a bell is not ‘used up’ when the bell is struck, and as long as you keep striking it it will continue to make its characteristic sound. Frugally, using surplus metal cast as an extension to the barrel of the cannon and intended to be cut off before the boring, Rumford set out to measure just how much heat was produced, using a dull drill bit to make the experiment more impressive. By enclosing the metal cylinder in a wooden box full of water, he could measure the heat released by seeing how long it took for the water to boil, and he delighted in the astonishment expressed by visitors in seeing large quantities of cold water quickly brought to the boil in this way without the use of any fire. But, as he also pointed out, this was not an efficient way to heat water. His horses had to be fed, and if you really wanted to boil water, a more efficient way to do so would be to dispense with the horses and burn their hay directly under the water. With this almost throwaway remark, he was on the edge of understanding the way in which energy is conserved but can be converted from one form to another.

Repeating the experiment over and over (emptying the hot water away and replacing it with cold), Rumford found that it always took the same time to boil the same amount of water using the heat generated by friction in this way. There was no sign at all of the ‘caloric’ being used up like water from a sponge. Strictly speaking, these experiments are not absolute proof that an inexhaustible supply of heat can be generated in this way, because they did not literally go on for ever – but they were very suggestive, and were perceived at the time as a major blow to the caloric model. He also carried out a series of experiments which involved weighing sealed bottles containing various fluids at different temperatures and establishing that there was no connection between the ‘amount of heat’ in a body and its mass, so nothing material could be flowing in or out as the body was cooled or heated. Rumford himself did not claim to understand what heat is, although he did claim to have shown what it is not. But he did write:

It appears to me to be extremely difficult, if not quite impossible, to form any distinct idea of any thing, capable of being excited and communicated in the manner the Heat was excited and communicated in these experiments, except it be MOTION.¹⁴

This sentence exactly fits the modern understanding of the association between heat and the motion of individual atoms and molecules in a substance; but, of course, Rumford had no idea what the kind of motion associated with heat was, so the statement is not quite as prescient as it seems. Rather, it was evidence from experiments like this that helped to establish the idea of atoms in the nineteenth century. And one reason why science did progress so rapidly in the nineteenth century was that by the end of the 1790s it was obvious to all but the most blinkered of the old school that the ideas of phlogiston and caloric were both dead and buried.

In terms of understanding the place of humankind in space and time, however, the most significant development in the last decades of the eighteenth century was the growing understanding of the geological processes that have shaped the Earth. The first version of the story was largely pieced together by one man, the Scot James Hutton, whose lead was then followed up in the nineteenth century by Charles Lyell. Hutton was born in Edinburgh on 3 June 1726. He was the son of William Hutton, a merchant who served as City Treasurer for Edinburgh and also owned a modest farm in Berwickshire. He died while James was very young, so the boy was raised by his mother alone. James attended the High School in Edinburgh and took arts courses at the university there before being apprenticed to a lawyer at the age of 17. But he showed no aptitude for the law and became so deeply interested in chemistry that within a year he was back at the university studying medicine (the nearest thing then available to chemistry, as typified by the work of people like Joseph Black). After three more years in Edinburgh, Hutton moved on to Paris and then to Leiden, where he received his MD in September 1749; but he never practised medicine (and probably had never intended practising medicine, which was for him just a means to study chemistry).

Hutton’s inheritance included the farm in Berwickshire, so on his return to Britain he decided he ought to learn about modern farming practices, and in the early 1750s, he went off first to Norfolk and then to the Low Countries to bring himself up to date, before heading back to Scotland, where he applied the techniques he had learned to turn a rather unprepossessing farm well supplied with rocks into an efficient, productive unit. All of this outdoor activity had triggered an interest in geology, and Hutton had also kept up his chemical interests. Chemistry came up trumps when a technique he had invented years before in collaboration with a friend, John Davie, was developed by Davie into a successful industrial process for the manufacture of the important chemical sal ammoniac (ammonium chloride, used in, among other things, preparing cotton for dying and printing) from ordinary soot. With money coming in from his share of the proceeds from the sal ammoniac process, in 1768, at the age of 42, Hutton, who never married, rented out his farm and moved to Edinburgh to devote himself to science. He was a particular friend of Joseph Black (just two years younger than Hutton), and was a founder member of the Royal Society of Edinburgh, established in 1783. But what he is best remembered for is his suggestion that the Earth had been around for much longer than the theologians suggested – perhaps for ever.

From his study of the visible world, Hutton concluded that no great acts of violence (such as the Biblical Flood) were needed to explain the present-day appearance of the globe, but that if enough time were available everything we see could be explained in terms of the same processes that we see around us today, with mountains being worn away by erosion and sediments being laid down on the sea floor before being uplifted to form new mountains by repeated earthquake and volcanic activity of the kind we see today, not by huge earthquakes which threw up new mountain ranges overnight. This became known as the principle of uniformitarianism – the same uniform processes are at work all the time and mould the surface of the Earth continually. The idea that occasional great acts of violence are needed to explain the observed features of the Earth became known as catastrophism.¹⁵ Hutton’s ideas flew in the face of the received geological wisdom of his time, which was a combination of catastrophism and Neptunism, the idea that the Earth had once been completely covered by water, particularly promoted by the Prussian geologist Abraham Werner (1749–1817). Hutton marshalled his arguments with care, and presented an impressive case for uniformitarianism in two papers read to the Royal Society of Edinburgh in 1785 and published in 1788 in that society’s Transactions (the first paper was presented by Black to the March 1785 meeting of the Society; Hutton himself read the second paper in May, a few weeks before his fifty-ninth birthday).

Hutton’s proposals brought severe (but ill-founded) criticism from the Neptunists in the early 1790s, and in response to these criticisms Hutton, though now in his sixties and unwell, developed his arguments in the form of a book, Theory of the Earth, published in two volumes in 1795. He was still working on a third volume when he died on 26 March 1797, in his seventy-first year. Unfortunately, although Hutton made a carefully argued case supported by a wealth of observational facts, his writing style was largely impenetrable, although the book did contain a few striking examples. One of the best of these concerns the Roman roads still visible in Europe some 2000 years after they were laid down, in spite of the natural processes of erosion going on all that time. Clearly, Hutton pointed out, the time required for natural processes to carve the face of the Earth into its modern appearance must be vastly longer – certainly much longer than the 6000 years or so allowed by the then-standard interpretation of the Bible. Hutton regarded the age of the Earth as beyond comprehension, and in his most telling line wrote ‘we find no vestige of a beginning – no prospect of an end’.

Such flashes of clarity were rare in the book, though, and with Hutton dead and no longer around to promote his ideas, which came under renewed and vigorous attack from the Neptunists and Wernerians, they might have languished if it had not been for his friend John Playfair (1748–1819), then professor of mathematics at Edinburgh University (and later professor of natural philosophy there). Picking up the baton, Playfair wrote a masterly, clear summary of Hutton’s work, which was published in 1802 as Illustrations of the Huttonian Theory of the Earth. It was through this book that the principle of uniformitarianism first reached a wide audience, convincing all those with wit to see the evidence that here was an idea that had to be taken seriously. But it literally took a generation for the seed planted by Hutton and Playfair to flower, since the person who picked up the baton of uniformitarianism from Playfair was born just eight months after Hutton died.

^1.See, for example, Chapter 9.

^2.This method of ‘making’ static electricity by friction is the reason why a child’s balloon rubbed on a woollen sweater can be made to stick to the ceiling, and why your hair can become electrified by brushing it.

^3.Incidentally, Euler really did go blind through looking at the Sun, just as all books of popular astronomy warn you can happen. The warning is based on fact!

^4.Michell, something of a polymath, first made his name by his investigation of the large earthquake that struck Lisbon in 1755, showing that the disturbance originated from beneath the Earth’s crust, out under the Atlantic Ocean, and established that earthquakes had nothing to do with atmospheric disturbances, as had previously been thought. He would probably have achieved even more in science, but in 1764 he gave up his post as professor of geology in Cambridge and became rector of a parish at Thornhill, in Yorkshire.

^5.In this, as on many other occasions, Laplace was stimulated by discussing the problem with Joseph Lagrange (1736–1813), a mathematician whose work on group theory and development of a mathematical function (the Lagrangian) which characterizes the path (or trajectory) of a particle proved immensely valuable to twentieth-century physicists.

^6.English translation from Gillispie.

^7.Quoted by Gillispie.

^8.It’s because the Earth is more dense than the Sun that Laplace came up with a figure of 250 times the diameter of the Sun, whereas Michell came up with twice that number.

^9.The term was actually introduced in 1834, by William Prout (1785–1850).

^10.The Holy Roman Empire finally came to an end in August 1806, as a side effect of the Napoleonic wars, when the last Emperor, Francis II (the one who got the job in July 1792), abdicated and became Francis I of Austria alone. Rumford was left as Count of an Empire that didn’t exist.

^11.Austria was the major central European power at this time, of course.

^12.He also met Joseph Guillotin, inventor of the guillotine, but not, presumably at the same social gathering as Mme Lavoisier. Rumford described M Guillotin as ‘a very mild, polite humane man’; remember that he invented his machine as a more merciful alternative to hanging.

^13.The modern explanation is that when the ball is fired, energy from the explosion goes into making the ball move, so less energy is available to be dissipated as heat in the cannon.

^14.Quoted by Brown.

^15.Both these terms are still misused by people trying to discredit rival ideas; the most important point of confusion is that because the history of the Earth is so long, events that seem rare and dramatic on a human timescale (such as large meteors hitting the Earth), and which are certainly catastrophic in the everyday meaning of the word, are both normal and, in geological terminology, uniformitarian as far as the history of the planet is concerned. It’s all a matter of perspective. To a butterfly that lives only for one day, nightfall is a catastrophe; to us, it is routine. To us, a new Ice Age would be a catastrophe; to Planet Earth, it is routine.