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In praise of Lord Kelvin

17 Dec 2007

Lord Kelvin — who died 100 years ago today — was a successful inventor, a wealthy businessman and perhaps the most important physicist of the 19th century. David Saxon explains how Kelvin played key roles in everything from thermodynamics and electric lighting to transatlantic telecommunication and the age of the Sun.

Inventor, businessman and physicist

A physicist visiting the city of Glasgow for the first time is often heard to wonder, “Is everything here named after Lord Kelvin?” With places like Kelvinside, Kelvindale and Kelvingrove, it certainly feels like that, but it is really the other way around. The great physicist, who died 100 years ago on 17 December 1907, took the title Baron Kelvin of Largs from the River Kelvin that curls around the foot of the University of Glasgow’s spectacular campus. Prior to his enoblement in 1892 as the first ever scientist peer, he was William (later Sir William) Thomson.

Born in Belfast in 1824, Kelvin moved to Glasgow in 1830 when his father, James Thomson, was appointed to the chair of mathematics at the university. At the age of 10, Kelvin enrolled at the university as its youngest ever student. Ironically, he is also the university’s oldest ever student — after retiring, aged 75, he immediately re-registered as a student; such was his interest in physics.

Personal fortune

In 1840, Kelvin left for Cambridge University before returning to Glasgow six years later to become professor of natural philosophy, a position he held for 53 years. Along the way, Kelvin amassed a personal fortune as an inventor and investor in new technologies such as electrical lighting.

Above all, Kelvin was the dominant figure in science in the second half of the 19th century. Indeed, he is buried in Westminster Abbey next to Isaac Newton, and a nave window there pays tribute to him as “Engineer, Natural Philosopher.” To quote one of Kelvin’s early biographers, Alexander Russell: “His work lives and will continue to live. To him it has been given to make history which will live so long as intelligent man survives on earth. As the years roll on our indebtedness to him increases.”

With Kelvin’s work on Fourier series, the classical physics of continuous media was born.

Despite his greatness, Kelvin’s achievements are often unheralded and he is remembered for his reactionary approach to the new physics that emerged in the last decade of his life, epitomized by the crisp statement, “X-rays are a hoax.” To appreciate his achievements, we need to go back more than half a century to 1841, when at the age of 16 he wrote his first scientific paper, based on his correspondence with Philip Kelland, professor of mathematics at Edinburgh University. Kelland and others had argued that mathematical instabilities at sharp boundaries meant that Fourier series could not be used to solve the partial differential equations that describe the flow of heat. Kelvin proved otherwise and thus the classical physics of continuous media was born.

Kelvin’s first paper is all the more remarkable because at the time there was no firm understanding of what heat actually was — a mystery that began to unravel two years later when James Joule showed that work was the mechanical equivalent of heat. Indeed, crucial to Kelvin’s approach was that he took to heart Fourier’s message that one can describe in mathematics the behaviour of heat without knowing precisely what heat is. Kelvin continued his study of heat and in 1848 he introduced the word “thermodynamics”.

What is energy?

By the mid 19th century the demands of the industrial revolution had put the “standard model” of physics in a crisis surrounding the question “What is energy?” In particular, the development of the steam engine had thrown the issue of energy and how to harness it into strong focus. However, what we now know as the second law of thermodynamics had yet to be formalized. Without a clear understanding of the roles of energy and entropy in thermodynamic processes, the theories of Joule and Sadi Carnot appeared to allow the construction of limitless energy sources from “perpetual motion” machines.

The key discovery that overcame this paradox of perpetual motion was actually made by Kelvin’s brother James Thomson, who was professor of engineering at Glasgow. James was two years older than Kelvin and discovered that the temperature at which ice melts falls when external pressure is applied — we now know that this is why ice skates work.

With this observation the thermodynamic contradictions of the past vanished and the first and second laws of thermodynamics could at last be written down. An absolute scale of temperature was defined and the absolute zero (the [unattainable] minimum temperature) determined. The first and second laws meant that physics could be rewritten in terms of energy. Indeed, the terms “kinetic” and “potential” energy were introduced by Kelvin and the Edinburgh physicist Peter Tait, with whom he co-authored Treatise on Natural Philosophy in 1867 — the first textbook on physics.

The second law of thermodynamics can be stated in various ways that turn out to be logically equivalent statements. Kelvin’s 1851 formulation is: “It is impossible, by means of an inanimate agency, to derive mechanical effect from any portion of matter by cooling it below the temperature of the coldest of the surrounding objects.” The law has stood the test of time and the efforts of many would-be inventors. Indeed, it has been argued that everything we know in science may be wrong, except the first and second laws of thermodynamics, which must be right. In the simplest layman’s paraphrase, the laws state: “you cannot get something for nothing” and “you cannot even break even”.

Epic undertaking

Kelvin was also successful at applying his considerable intellect to solving the problems of industry. His most notable enterprise was the laying of the first transatlantic telegraph cable between Ireland and Newfoundland in 1858–1866. This was an epic undertaking with huge practical difficulties and Kelvin did much of the original scientific work and invention that made it possible.

A fundamental problem facing the Atlantic Telegraph Company, of which Kelvin was a director, was that no one knew how deep the ocean was. Attempts to measure the depth by simply dropping a very heavy weight at the end of a cable always resulted in the cable reel breaking. Kelvin solved this problem by inventing a compact device that could be lowered on a piano wire and measured the pressure difference between the surface and sea floor, from which the depth could be calculated.

The achievement of the transatlantic cable shrank the world more than anything before or since.

Kelvin also solved the problem of extracting the very weak telegraph signal at the receiving end of the cable. An earlier attempt at doing so by Edward Whitehouse, chief electrician of the Atlantic Telegraph Company and Kelvin’s rival in the development of telegraph technology, ended in disaster in 1858. Whitehouse raised the signal voltage ever higher until the insulation failed — destroying the first cable and leading to a parliamentary enquiry.

Kelvin’s ultimate strategy for signal extraction was to develop a receiving and recording device that required minimal signal power — the “siphon recorder”. A precursor of the modern inkjet printer, the recorder’s only moving part was a jet of ionized ink that recorded the Morse code signal on paper.

The achievement of the transatlantic cable shrank the world more than anything before or since. It has the same logical structure as e-mail — digitally encoded, packet switched and seeking the least crowded route. Kelvin’s contributions earned him his knighthood and set him on a path to riches and invention after invention.

Inventions and theories

In 1884, at the age of 60, Kelvin joined forces with the Glasgow instrument maker James White to create a company that would become Kelvin and James White Ltd. Perhaps its most famous product was Kelvin’s compass for iron ships. This was the first instrument that could provide a true reading of magnetic North in spite of the permanent magnetic moment of the ship and the additional moment induced in the hull by its orientation in the Earth’s field.

Kelvin played important roles in the burgeoning science and technology of electricity. He worked to refine the accuracy of electrical units of measurement, ultimately chairing the committee that named the Ampere, Volt, Ohm, etc as we know them today.

Kelvin also pioneered electric light, and in 1881 made his home in Glasgow the first house in the world to be fully lit by electricity, using 106 lamps. That same year he began research and development work with Joseph Swan, who was a pioneer in the design and manufacture of incandescent light bulbs. International students flocked to work in Kelvin’s laboratory including Gerard Philips, the co-founder of a Dutch light bulb manufacturer that would later become Royal Philips Electronics.

Kelvin had a keen interest in the geosciences and was the first to apply mathematics to the question of the ages of the Earth and the Sun. He approached the problem of the Sun by looking at all known energy sources and calculating how long they could sustain the Sun’s heat output.

Kelvin estimated the age of the Earth by calculating how long mountains could survive against wind and water erosion.

At one point the most promising energy source for the Sun was gravitational shrinkage. Kelvin had to abandon this theory because he knew that Alexander the Great had seen a solar eclipse when he crossed the River Oxus in 329 BC. This put an upper limit on the size of the Sun at that date, suggesting that the Sun was not shrinking fast enough to provide the required power. Kelvin estimated the age of the Earth by calculating how long mountains could survive against wind and water erosion.

Of course, Kelvin did not know about the mountain-building processes of plate tectonics or the nuclear fusion that powers the Sun, and therefore his ages were hugely underestimated. He believed the Earth to be a mere 100 million years old, for example, which caused uproar amongst evolutionists, leading to a controversy that lasted some time. Although his answers were wrong, Kelvin’s methods were right: the quantitative approach was both new and correct, but the data were incomplete.

Aware of his failings

Despite his great advances in science and engineering, towards the end of his life Kelvin was acutely aware of the failings of the classical physics that he was so instrumental in creating. He shared this sentiment at a celebration of his 50th anniversary as professor in words that surely would have shocked his audience: “One word characterizes the most strenuous of the efforts for the advancement of science that I have made perseveringly during 55 years. That word is failure. I know no more of electric and magnetic forces or of the relation between aether, electricity and ponderable matter, or of chemical affinity than I knew and tried to teach to my students of natural philosophy 50 years ago in my first session as professor.”

This lament harks back to his beginnings, to the joy that Kelvin felt in learning that you can describe how heat flows in mathematics without ever knowing what heat is. This is the triumph and tragedy of classical physics. It is brilliant phenomenology, but falls short of explaining how the structure of atoms forces the behaviour of the material.

Kelvin’s era was closing. It would be a task for others to elucidate the new phenomena — the electron, X-rays, radioactivity, the photoelectric effect, relativity — that came crowding into his last decade. We should honour him for what he achieved and for his yearning for what remained to be achieved. He felt himself to be like Isaac Newton in old age, playing with the odd attractive pebble on a beach while an ocean of truth lay undiscovered before him, and he felt the frustration of this.

Boundless energy

Kelvin’s life was characterized by boundless energy that would keep a whole laboratory of scientific assistants jumping and would lead to more than 650 scientific papers and to 75 patents. A modern comparator could be Richard Feynman. Both were brilliant mathematical physicists and problem solvers. Both made major contributions to many areas of physics, had a wide interest in other areas and were inspirational teachers.

If we are to look for one thing to remember Kelvin by, scientists might pick the absolute temperature scale as his crowning achievement; members of the public might opt for the telegraph cable across the ocean. Russell’s eulogy, “His work lives and will continue to live”, is not inappropriate for the scale of his achievements.

About the author

David Saxon is Kelvin Professor of Physics, University of Glasgow.

Kelvin in his own words

“When you are face to face with a difficulty, you are up against a discovery.”
“The more you understand what is wrong with a figure, the more valuable that figure becomes.”
“To measure is to know.”
“If you cannot measure it, you cannot improve it.”
“When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind.”
“I am never content until I have constructed a mechanical model of the subject I am studying. If I succeed in making one, I understand, otherwise I do not.”
“There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.”

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