The Man Who Changed Everything

He still had the fascination with the whole physical world that he had felt as a child. In his view, the proper study of science required full use of all one’s physical senses and mental powers, both analytical and imaginative. And science was universal, not just something that went on in laboratories. All the same, laboratories had a vital role in teaching and research and he wanted the Cavendish to meet the highest standards in both.

Towards the end of the inaugural lecture he emphasised the cultural significance of science:

We admit that the proper study of mankind is man. But is the student of science to be withdrawn from the study of man, or cut off from every noble feeling, so long as he lives in intellectual fellowship with men who have devoted their lives to the discovery of truth, and the results of whose enquiries have impressed themselves on the ordinary speech and way of thinking of men who have never heard their names? Or is the student of history and of man to omit from his consideration the history of the origin and diffusion of those ideas which have produced so great a difference between one age of the world and another?

All new ventures have their detractors, and James had his full share with the Cavendish project. One diminishing but still powerful school of critics held that, while experiments were necessary in research, they brought no benefit to teaching. A typical member was Isaac Todhunter, the celebrated mathematical tutor, who argued that the only evidence a student needed of a scientific truth was the word of his teacher, who was ‘probably a clergyman of mature knowledge, recognised ability, and blameless character’. One afternoon James bumped into Todhunter on King’s Parade and invited him to pop into the Cavendish to see a demonstration of conical refraction. Horrified, Todhunter replied: ‘No, I have been teaching it all my life and don’t want my ideas upset by seeing it now!’².

Despite such dismal predictions, James had no difficulty in gathering a set of talented researchers. Some gave up good posts elsewhere to come to work with him. Had James wanted, he could easily have set people to work on problems arising directly from his own investigations. But that was not his way. He had not taken the job to found a Maxwell school but to help physical science advance on a broad front and to help individual students develop their own powers; and he believed that these ends would be best served if everyone was free to follow his own path. There may have been another reason. It was important for the Cavendish to establish its reputation with some early successes, and the kinds of investigation suggested by his own electromagnetic theory were too difficult and risky for this purpose.

James gave beginners problems that were interesting but not too daunting, started them off and kept a fatherly interest in progress. Some of his students were already experienced researchers. For them he would suggest a topic if asked, but if someone had a firm idea of what he wanted to do James simply encouraged him to get on with it. As we have seen, James’ talents as a lecturer were limited. But as a supervising coach in a laboratory he was truly inspirational. Advice from one of the greatest scientific minds of all time was dispensed with unfailing generosity and humour. His students loved him.

The resulting programme of research work consisted in the main of high-precision measurements of fundamental physical quantities. This was important, if unspectacular, work. The subject of electricity and magnetism was still in need of experimental consolidation in some basic areas. For one thing, Ohm’s law, the basic law of electrical circuits, had never been thoroughly verified by experiment and was now being called into question. What was in doubt was whether the resistance of a given wire (the ratio of voltage to current) under fixed conditions would be the same for any value of current. A student from Aberdeen, George Chrystal, took this work on and was immediately faced with a problem: resistance was known to vary with temperature, and the more current a wire carries, the hotter it gets. Undaunted, he found a way to compensate for the temperature effect and carried out tests using a vast range of currents: the smallest was barely measurable and the largest was great enough to make the wire red hot. The work had to be done with immense care and took 5 months but Ohm’s law came out triumphant. Over the whole range of currents the resistance of his sample wire changed by less than one part in a million million.

Even more impressive than its early research results was the way it developed the talents of its researchers. Many went on to distinguish themselves elsewhere. Among James’ students were Richard Glazebrook, who became the founding Director of the National Physical Laboratory; William Napier Shaw, who got meteorology established as a profession in Britain; James Butcher, who became a successful lawyer and a Tory Member of Parliament and was ennobled as Lord Danesfort; Donald MacAlister, who became President of the General Medical Council and Principal of Glasgow University; and a clutch of professors at other universities, among whom Ambrose Fleming invented the thermionic valve and J. H. Poynting the vector that bears his name ^k.

James’ heart cannot have leapt with joy when, in 1874, the Duke passed him a mass of unpublished accounts of electrical experiments done by his great uncle Henry Cavendish between 1771 and 1781, with a suggestion that he consider editing them for publication. He already had his hands full with the Laboratory and other commitments, and wanted time to pursue his own research. But after a scan through the papers he was captivated by the elegance, originality and power of Cavendish’s work. Here were some of the finest experiments ever performed; they included important discoveries which had since been attributed to others. To James, scientific facts were incomplete without the knowledge of how they came to be discovered. The process of discovery held as much interest as the result. Scientific history was at least as important as political history and needed to be complete. He decided to undertake the huge task of editing the papers himself —‘walking the plank’ with them, as he put it in a letter to William Thomson.

Most writers about Maxwell regret that he gave so much time in his last few years to this work, rather than to his own research. From our distant viewpoint it does indeed seem a regrettable decision. But James was not to know he had only 5 years to live. His ideas on electromagnetism and gas theory were still developing and could safely be consigned for a while to ‘the department of the mind conducted independently of consciousness’, to be ‘run off clear’ later. And perhaps we should in any case judge the decision by his own motto, ‘It’s no use thinking of the chap you might have been’. He did what he did because he was a man of genuine altruism and generous spirit.

Henry Cavendish, by contrast, was the meanest curmudgeon imaginable. He had lived as a recluse, venturing out only occasionally for scientific meetings and communicating with his domestic staff by written notes. Women servants were sacked if they allowed themselves to come into his sight. An acquaintance said: ‘He probably uttered fewer words in the course of his life than any man who ever lived to fourscore years, not at all excepting the monks of La Trappe’³. But his scientific work, begun with his father and continued for many years alone, was sublime. Sometimes he published his findings but more often did not. He could never remember what he had published and what he hadn’t, and often confused readers by referring to earlier unpublished results. Cavendish’s genius was in performing amazingly accurate experiments with the crudest of equipment by dint of brilliant design and single-minded determination. In one famous experiment he had discovered that water was a compound, not an element. In another he had measured the density of the earth to within 2% of its true value. But he had published almost none of his electrical work and the great bulk of it came to James in the form of manuscripts about 100 years old.

Cavendish’s electrical experiments were a revelation. Among a series of outstanding results, he had demonstrated the inverse square law of force between electric charges more effectively than Coulomb, after whom the law was named, and he had discovered Ohm’s law 50 years before Ohm. The way he did this in the days before batteries and current meters evokes images from a Gothic novel. He charged up an electrical storage device, connected it to a circuit with two open terminals, discharged it through his body by putting a hand across the terminals and noted how far up his arm he could feel the shock. His staunch servant Richard would then take his place and Cavendish would make a note of his reactions. The procedure was repeated using different circuit arrangements, each time measuring the current by the severity of the shock.

The experiment was not as horrific as it sounds. James repeated it in the Cavendish Laboratory and found that horny-handed rowers had a higher electrical resistance than the other students. One day a distinguished American called in to see James and was surprised to find the great man with sleeves rolled up, preparing to wire himself in. When invited to have a go himself the visitor took fright and left, saying ‘When an English man of science comes to the United States we do not treat him like that’⁴.

Another big commitment James took on was the joint scientific editorship, with T. H. Huxley, of the 9th edition of the Encyclopaedia Britannica. Like his work on the Cavendish papers, this was a labour of love. He believed passionately in the value of good popular presentation of science and wrote many of the encyclopaedia articles himself, as well as others for journals such as Nature. He also refereed many papers and reviewed many books. It was a pleasure to review good work but when necessary he did not shirk from giving a book a trouncing.

An instance was Practical Physics, Molecular Physics and Sound by Frederick Guthrie, Professor of Physics at the Normal School of Science, Kensington. James thought that Guthrie had done harm by giving readers the jargon of science without the substance, and he pulled no punches in his review for Nature⁶. But he felt sorry for Guthrie; the chap had been doing his best, albeit misguidedly, and to get a public mauling from a heavyweight like Maxwell was a humiliation. Three weeks later, Nature published a remarkably cheerful letter from Guthrie. ‘Some well-meaning friend has sent me a copy of the inclosed. There appear to be various opinions as to the authorship. It has even been suggested that Professor Maxwell, with that sense of humour for which he is so esteemed and with a pardonable love of mystification, is himself the author’. The poem followed:

WORRY, through duties Academic,
It might ha’e been
That made ye write your last polemic
Sae unco keen:

Or intellectual indigestion
O’ mental meat,
Striving in vain to solve some question
Fro’ ‘Maxwell’s Heat’.

Mayhap that mighty brain, in glidin’
Fro’ space tae space,
Met with anither, an’ collidin’
Not face tae face,

But rather crookedly, in fallin’
Wi’ gentle list,
Gat what there is nae help fro’ callin’
An ugly twist.

If ’twas your ‘demon’ led ye blindly,
Ye should not thank him,
But gripe him by the lug and kindly
But soundly spank him.

Sae, stern but patronising daddie!
Don’t ta’e’t amiss,
If puir castigated laddie
Observes just this:-

Ye’ve gat a braw new lab’ratory
Wi’ all the gears,
Fro’ which the warld is unco’ sorry,
Maist naught appears.

A weel-bred dog, yoursel’ must feel,
Should seldom bark.
Just put your fore paws tae the wheel,
An’ do some Wark.

The only plausible explanation of this odd but endearing little comedy is that the poem was James’ way of showing fellow-feeling with Guthrie, at the same time defusing the tension by poking fun at himself. Guthrie would guess at once who had written the poem but James was implicitly inviting him to be a conspirator in the scheme by sending it to Nature with the pretence that he was mystified. Everyone would see through the pretence, but that was part of the joke.

When it came to books for students, James’ ideas on how it should be done are nowhere better shown than in a little gem of a book published in 1877, Matter and Motion. It deals with the foundations of dynamics, is written in simple, jargon-free language and can be followed by someone who has done a little advanced school mathematics. Yet it is in no way ‘dumbed down’; the reader is required to think. It is an aid to true understanding rather than to passing exams or impressing dinner companions with one’s knowledge of the jargon. It bears the Maxwell stamp just as surely as do his great theories.

He felt at home amid the buzz and camaraderie of life at Cambridge. When time allowed, he attended a small essay club that was rather like the ‘Apostles’ club he had belonged to as a student, but composed of middle-aged professors and dons. He relished the free-wheeling discussions and contributed several essays on philosophical themes. In one he dismisses the belief, then widely held, that scientific laws implied a mechanically deterministic universe, in which the future is predictable, and in doing so gives a remarkable statement of the basis of chaos theory, which mathematicians did not begin to develop until 100 years later:

When the state of things is such that an infinitely small variation of the present state will alter only by an infinitely small quantity the state at some future time, the condition of the system, whether at rest or in motion, is said to be stable; but when an infinitely small variation in the present state may bring about a finite difference in the state of the system in a finite time, the condition of the system is said to be unstable.

It is manifest that the existence of unstable conditions renders impossible the prediction of future events, if our knowledge of the present state is only approximate and not accurate.⁷

—an exact description of the problem faced by today’s weather forecasters.

James’ colleagues were in no doubt that they had a remarkable man in their midst. Lewis Campbell gives us an idea of the kind of impression he made on them:

One great charm of Maxwell’s society was his readiness to converse on almost any topic with those he was accustomed to meet, although he always showed a certain degree of shyness when introduced to strangers. He would never tire of talking with boyish glee about the devil on two sticks and similar topics, and no one ever talked to him for five minutes without having some perfectly new ideas set before him; some so startling as to utterly confound the listener, but always such as to repay a thoughtful examination.

And he could still never resist a chance to poke a little fun. Sometimes the joke rebounded; Campbell reports:

On one occasion, after removing a large amount of calcareous deposit which had accumulated in a curiously colitic form in a boiler, Maxwell sent it to the Professor of Geology with a request that he would identify the formation. This he did at once, vindicating his science from the aspersion that his brother professor would playfully have cast on it.

When another of his fellow professors was to be honoured by a portrait which had been specially commissioned from the popular artist Lowes Dickinson by a group of colleagues and admirers, James was ready with a poem to mark the unveiling. The subject of the portrait was the great mathematician Arthur Cayley, who had invented the theory of matrices and the geometry of any number of dimensions. True to form, James managed to evoke the spirit of the occasion—which was a serious and heartfelt tribute to Cayley—and to make a joke of it at the same time:

O wretched race of men, to space confined!
What honour can ye pay to him, whose mind
To that which lies beyond hath penetrated?
The symbols he hath formed shall sound his praise,
And lead him on in unimagined ways
To conquests new, in worlds not yet created.

March on symbolic host! with step sublime,
Up to the flaming bounds of Space and Time!
There pause, until by Dickinson depicted,
In two dimensions, we the form may trace
Of him whose soul, too large for vulgar space,
In n dimensions flourished unrestricted.⁸

In his early 20s Rowland was the first person to find a rigorous magnetic analogy to Ohm’s law but had his work repeatedly rejected by the American Journal of Science. Exasperated, he sent his paper across the Atlantic to Maxwell, who saw its merit at once, had it published in the Philosophical Magazine, and wrote back with congratulations and suggestions. When Rowland applied for a professorship at the new Johns Hopkins University in Baltimore, he showed his correspondence with Maxwell to the University President, who thought it ‘worth more than a whole stack of recommendations’ and gave him the job. Hearing that Rowland was to make a working tour of Europe starting that summer, James invited him to Glenlair. There they mulled over an idea for an experiment to show that a moving electric charge generated magnetic effects like those of a current in a wire. The following year, in Berlin, Rowland approached the august Helmholtz, asking for space in his superbly equipped laboratory to do the experiment. Helmholtz was reluctant, as the place was already bustling with high quality research, but once again Maxwell’s interest served as the strongest possible recommendation and the great professor decided to give the young American a basement room. The ambitious experiment used a rapidly spinning ebonite disc, a beam of light and a delicately suspended mirror. It succeeded magnificently. James was delighted for his young friend and celebrated the exploit in inimitable fashion with a poem:

The mounted disc of ebonite
Has whirled before, nor whirled in vain;
Rowland of Troy, that doughty knight,
Convection currents did obtain
In such a disc, of power to wheedle,
From its loved north the subtle needle.

’Twas when Sir Rowland, as a stage
From Troy to Baltimore, took rest
In Berlin, there old Archimage,
Armed him to follow up this quest;
Right glad to find himself possessor
Of the irrepressible Professor.

But wouldst thou twirl that disc once more,
Then follow in Childe Rowland’s train,
To where in busy Baltimore
He brews the bantlings of his brain ...

Although he was not himself a prolific inventor of technical devices, James was an enthusiastic admirer of inventors such as Charles Wheatstone, William Thomson, David Hughes, Thomas Edison and Alexander Graham Bell. When asked to give a public lecture in 1878, he chose to talk about the technological wonder of the day—Bell’s invention, the telephone. In typically whimsical fashion, he wove a picture of the telephone as a symbol of the cross-fertilisation of different sciences. One such science was elocution, the speciality of Graham Bell’s father, Alexander Melville Bell. Addressing the company in strong Gallowegian tones, James spoke of the elder Bell:

... his whole life has been employed in teaching people to speak. He brought the art to such perfection that, though a Scotchman, he taught himself in six months to speak English, and I regret extremely that when I had the opportunity in Edinburgh I did not take lessons from him.

His Treatise on Electricity and Magnetism is probably, after Newton’s Principia, the most renowned book in the history of physics⁹. It was published in 1873 and has been in continuous use ever since. In 1000 pages of crisply written text and mathematics it encompasses virtually everything that was known about electricity and magnetism. It has inspired most of the work done in the subject ever since. At first glance it looks like a text book; indeed, most modern texts are ultimately derived from it, although they often fail to match its clarity. But a closer look shows it to be something far more interesting. Sometimes Maxwell takes you along a path to a certain point, then, when you expect to go on, takes you back to the start and along a new path which leads to areas inaccessible from the first. The book is not an atlas but an explorer’s report. James had written it for himself as well as for others—to consolidate his own knowledge as a base for further exploration. He had begun an extensive revision of the Treatise at the time of his early death.

In the Treatise James made an important new prediction from his electromagnetic theory—that electromagnetic waves exert a radiation pressure. Bright sunlight, he calculated, presses on the earth’s surface with a force of around 4 pounds per square mile, equivalent to 7 grams per hectare. This was too tiny a value to be observable in everyday life and its detection posed a challenge to experimenters. Eventually, in 1900, the Russian physicist Pyotr Lebedev succeeded, and confirmed James’ prediction. Although small on an earthly scale, radiation pressure is one of the factors that shape the universe. Without it there would be no stars like our sun—it is internal radiation pressure that stops them from collapsing under their own gravity. James’ discovery also helped to explain a phenomenon that had puzzled astronomers for centuries—why comets’ tails point away from the sun¹⁰.

He extended other aspects of his electromagnetic theory in the Treatise and, where possible, gave practical applications: for example, he explained the principles to be followed when correcting compass readings on iron ships and referred to the Admiralty manual on the subject. He also introduced quaternion notation into the electromagnetic field equations, making them look much like they do in our modern vector notation. But knowing that the compact new quaternion format would look strange to most readers, he included the old cartesian (x, y, z) format equations as well. One outcome of this was that he ran out of letters, having used up the entire Roman and Greek alphabets. He resorted to Roman letters in German Gothic script for his new variables, with the result that the quaternion equations in the Treatise have a strange Wagnerian aura.

James’ enthusiastic follower Ludwig Boltzmann had published two superb papers on gas theory in 1868 and 1872. Taking James’ idea of the velocity distribution of molecules in a gas, he had derived a more general law for their energy distribution—now known as the Maxwell-Boltzmann distribution. He had also generalised James’ principle for the equipartition of energy, showing that it should be divided equally not only between modes of linear and rotational movement but among all the independent components of motion in the system.

James had inspired Boltzmann; now he was inspired in turn. The new results were wonderful, even though he found the writing rather long-winded—he re-derived Boltzmann’s main result for Nature on a single page. James responded with a masterful paper: On Boltzmann’s Theorem on the Average Distribution of Energy in a System of Material Points. This work, more than any other, laid the foundations for the development by Boltzmann and others of statistical mechanics—an esoteric but useful subject which enables physicists to explain the properties of matter in terms of the behaviour, en masse, of its molecules. He derived the velocity and energy distributions in a powerful new way, which gave the equipartition principle as a by-product. One of the key ideas in the paper was what came to be called the method of ensemble averaging, in which the actual system under study is replaced by a statistically equivalent arrangement that is much easier to analyse. The highly mathematical analysis concluded with a practical application directly from the theory: gaseous mixtures could be separated by means of a centrifuge. Many years later this became a standard commercial technique.

One big problem remained. Maxwell and Boltzmann’s theory still predicted a different value for the ratio of the specific heats of air at constant pressure and at constant volume from that measured in experiments¹¹. In fact, things were getting worse. From the new technique of spectroscopy developed by Kirchhoff and Bunsen came evidence that gas molecules could vibrate as well as rotate. When this effect was allowed for, the ratio of specific heats predicted by the theory was even further from the observed value. James could not explain the discrepancy and was not convinced by various ingenious attempts by Boltzmann. Summing up the situation in Nature, he concluded that ‘something essential to the complete statement of the physical theory of molecular encounters must have hitherto escaped us’ and that the only thing to do was to adopt the attitude of ‘thoroughly conscious ignorance that is the prelude to every real advance in science’.

He was right, as usual. The explanation came 50 years later from quantum theory. By the equipartition principle, Maxwell and Boltzmann’s theory held that in the course of billions of molecular collisions kinetic energy is exchanged between all the different modes of motion—linear, rotational and vibrational—so that everything evens out. If energy were infinitely divisible gases would indeed behave this way, but, as we now know, energy can only be exchanged in discrete packets, or quanta. And the quantum size is different for each mode of motion, the vibrational quanta being the largest. In very hot air many of the molecular collisions are violent enough to supply the quanta of energy needed to start the nitrogen and oxygen molecules vibrating, but at lower temperatures most of the collisions are too feeble for this to happen and so vibrational modes are ‘frozen’ out of the exchanges and play no part in the specific heat. At lower temperatures still, the rotational modes are also frozen out. In consequence of all this, the ratio of the specific heats at constant pressure and constant volume depends on a complex set of interacting factors, rather than on the simple formula James and Boltzmann had been using.

In 1874 William Crookes caused a sensation with his ‘radiometer’—a toy-like device that seemed to work by magic. It was a little paddle wheel with blades silvered on one side and blackened on the other, inside a glass bulb from which most of the air had been pumped out. When exposed to light or radiant heat the paddle wheel turned. The public and scientists alike were fascinated. No one could explain how it worked.

The mystery deepened when it became clear that Maxwell’s radiation pressure was not what drove the wheel: the force on the paddle blades was much too large and in the wrong direction! Scientists everywhere made their own radiometers and tried all manner of design variations in the search for clues. There were various speculative theories but the first real breakthrough was made by James’ friend P. G. Tait and his colleague James Dewar (who had discovered the element thallium and later invented the vacuum flask). Crookes had pumped out as much air as he could from the glass bulb but Tait and Dewar found that the radiometer effect depended on the small amount which was left behind. But still nobody knew how the remaining trace of rarefied gas drove the paddle wheel.

James now entered the arena. He applied his kinetic theory of gases but at first all he got was an apparently elegant proof that the gas in the bulb would quickly reach a stable temperature distribution so there would be no resultant force on the paddle blades. Then he realised that the gas must be acting on the part of the blades he had so far neglected—the edges. Convection currents from the hotter (blackened) to the cooler (silvered) sides would move along the blades and around the edges, where the gas molecules would interact with the surfaces and transfer some of their momentum to the paddle wheel. At very low gas pressures these ‘slip’ currents would become the dominant effect.

He embodied these findings in a much more general discussion in a paper for the Royal Society, On Stresses in Rarefied Gases Arising from Inequalities of Temperature, putting forward the slip current effect as an explanation of the paddle wheel’s movement but giving no formula for it. Here things might have stayed, but William Thomson, who refereed the paper, nudged him into trying to quantify the effect. James came up with a remarkably simple and useful formula based on the assumption that a fraction f of the gas molecules is absorbed by the surface and later evaporated off, while the remaining fraction (1—f) is reflected—the value of f depending on the type of gas and the type of surface. He issued this result and others in an appendix to the paper. It was his last published work, as the illness which was to take his life was by now asserting its grip.

The search for the secret of Crookes’ little radiometer generated discoveries and advances out of all proportion to its intrinsic importance. The biggest benefit of all turned out to be the improvement, led by Crookes himself, in the design of vacuum pumps. The ability to set up and maintain very low gas densities made possible many discoveries of the late nineteenth and early twentieth centuries, including that of the electron.

Martin Goldman reports a final twist to the radiometer story in The Demon in the Aether. The definitive solution to the puzzle was given in the 1920s by Chapman and Cowling. They showed that there is, after all, a force on the blades which would be sufficient to turn the paddle even if the slip current effect did not exist. Maxwell had made an incorrect simplification in his initial equations, which invalidated his conclusions about the radiometer but not his more general results. The irony is that had he not made this mistake he might have ignored the slip current effect altogether and his pioneering ‘f’ formula would have had to wait for another inventor.

While James was working on this paper he was asked by the Royal Society’s secretary, George Gabriel Stokes, to referee one by Osborne Reynolds which covered some of the same ground. This was awkward but as the papers differed in their main substance he decided that he could fairly referee Reynolds’ paper without holding back his own. Reynolds had made some errors but James thought the conclusions were broadly correct and recommended that it be published ‘after the author has had the opportunity to make certain improvements in it’. That done, he completed his own paper, which included a generous tribute to Reynolds. Meanwhile, Reynolds’ paper was delayed further by Thomson, the other referee, whose comments were vehemently critical. When James’ paper came out first Reynolds was livid. It seemed to him that the great Maxwell had played foul and he complained angrily to Stokes. His letter drew a stinging reply. Stokes was a good friend of James, who by this time was critically ill, and he rebuked Reynolds for what he saw as boorish behaviour. This served only to fuel poor Reynolds’ resentment. Had James lived longer he would probably have found a way to dispel the unpleasantness. As it was, Reynolds was probably the only person ever to harbour a grudge against him. Reynolds went on to do excellent work on the theory of fluids and is commemorated by the Reynolds number, which determines when fluid flow changes from smooth to turbulent.

At Cambridge the Maxwells lived at Scroope Terrace, a short walk from the Laboratory. Although the circumstances were similar, home life there was different from that in Kensington 10 years before. There were no home experiments, as James now had the grand new laboratory nearby. And his work responsibilities were much heavier; they could no longer go riding every afternoon. There was another change; Katherine began to suffer from poor health. She felt weak for much of the time and often needed nursing. James would sit with her while working on his manuscripts. For one 3 week spell he did got go to bed but slept in a chair at her bedside—yet worked with his usual energy during the day. Perhaps because of her illness, the cause of which was never found, she seems not to have been very welcoming to James’ colleagues and some of them took a dislike to her. To spare either her or his colleagues distress, James sometimes conducted business at the laboratory which might have been more congenially done over a cup of tea at home.

But perhaps twentieth century writers have made too much of such criticism. Mrs Tait was not the most reliable of witnesses: she used to say that Katherine tried to stop Maxwell’s scientific work, which is clearly nonsense. And there was a callous streak in cousin Jemima’s make-up: when her nephew and staunch friend Colin Mackenzie died in 1881 she kept her family away from the funeral because of rumours that he had been involved in some scandal. Colin was also a good friend to the Maxwells and has a further part to play in our story. Katherine was certainly no impediment to Maxwell’s continued friendship with Colin and with his other male cousins William and Charles Cay, who were regular visitors to Glenlair. One strong sign of mutual regard was that Katherine named her pony after Charles¹².

They spent about 4 months of each year at Glenlair. This gave James a chance to catch up with local developments and to fulfil his duties as Laird and as a leading citizen of the area. Riding was still their favourite exercise. Lewis Campbell reports the recollections of a neighbour:

Mr Ferguson remembers him in 1874, on his new black horse, ‘Dizzy’, which had been the despair of previous owners, ‘riding the ring’, for the amusement of the children at Kilquhanity, throwing up his whip and catching it, leaping over bars, etc.

At Glenlair, local issues had first call on his attention. It was at this time that James had his long-running losing battle with the economy-minded School Board who wanted to close the school at Merkland. But he also kept the postman busy emptying and replenishing the post box in the wall at the end of his drive. Many of his papers and articles were written at Glenlair, and he kept in touch with people who were working over the vacations at the Cavendish, advising on experiments.

As the end of the decade approached, James had reason to be pleased with the way things were going. He had not sought the post at the Cavendish but it had become an important part of his life. He took immense pride in the work of his young researchers. The Laboratory had confounded the sceptics and had generated a great swell of interest in science at Cambridge. His own theoretical ideas were still developing, and now that the great labour on the Henry Cavendish papers was finished he would have more time to pursue them. He enjoyed the variety and balance of his working life and interests: town and country, science and people, experiments and mathematics. And the curiosity about everything in the physical world which had driven him as a child to fire fusillades of ‘What’s the go o’ that?’ questions at his indulgent parents burned as strongly as ever. Maturity had honed his skill and strengthened his judgement without in any way dulling his freshness or enthusiasm. But the disease that had shortened his mother’s life struck again. The 1880s had promised to be fruitful years, but he did not live to see them.