Characters in Rutherford's Life

Sir William Thomson, first baron Kelvin

of Largs (1824-1907)

Born in Belfast, but settled with his parents in Glasgow at the age of 8, William Thomson spent his entire career in this city.

After an inevitable stint in Cambridge for his studies, he began at the age of 22 as professor of Natural Philosophy at the university of his adopted Scottish city. In his time, the term Natural Philosophy included everything that would later be called physics and chemistry. And William Thomson didn't have a beard yet.

Images :

Lord Kelvin vers 1896. Source : Wellcome Collection.
Lord Kelvin en 1846. Source : Lord Kelvin An account of his scientific life and work, Andrew Gray, 1908, page 64.
Lord Kelvin en 1871. Source : University of Glasgow.
Localisation de la rivière Kelvin à Glasgow. Source : Wikipédia.
Université de Glasgow en 1895. Source : Library of Congress Prints and Photographs Division Washington, D.C.

A major figure in the sciences of the second half of the 19th century, Lord Kelvin was a supporter of Ernest Rutherford during the first months of his career ... before becoming one of his most vocal opponents.

A true jack-of-all-trades, William Thomson left his mark in many fields of science: electricity, magnetism, astrophysics, thermodynamics and so on. If you are interested, you can go to see all the theories, equations and other notions bearing his name. Which name is not Thomson (too banal): it is under the surname Kelvin that this major figure of science has passed down to posterity. In 1866 he was indeed knighted and in 1892 he was elevated to the rank of baron. He then took the name of Lord Kelvin of Largs, taking inspiration from the Kelvin River which passes near his university.

This is how when using the Kelvin, unit of absolute temperature (which is a notion imagined by William Thomson), we are referring to a Scottish waterway 35 km long (which, given that it is not made of pure water and is subject to a certain agitation, should not freeze at 273.15 K as one might think (admit that you thought it)).

When Ernest Rutherford arrived in Cambridge in 1896, Kelvin was the scientific benchmark of the British Empire. It suffices to consider that the year of his birth, in 1871, the future Lord Kelvin is already 47 years old (and had a beard, but which is not yet white). In 1896, a quick calculation tells us that he is 72 (and still had a beard, very white now).

It is therefore a real honor for the young New Zealander to be able to count the sage of Glasgow among the few supporters that his first invention, hiswave detector, won. But the adventure will come to an end because of a competing project developed by an Italian named Guglielmo Marconi. The following years will be marked more by opposition than by cooperation between Kelvin and Rutherford.

It was the latter's new direction in the field of radioactivity that caused the controversy between the two men.

Indeed, the patriarch of British science did his best to question almost all of Rutherford's discoveries on this subject: the alpha and beta particles highlighted by the New Zealander were not, for the Scottish scientist, as various forms of electricity; radioactive decay did not exist, since atoms were eternally immutable; the energy that Rutherford claimed to come from radioactive materials was actually provided to them by the external environment...

As Kelvin attended almost all the scientific symposia, it was difficult for Rutherford to avoid confrontation. And even when the master of Glasgow was absent, he managed to transmit communications which still cast doubt on the notions developed by Rutherford.

The final point of opposition concerned the assessment of the age of the earth.

In the 1860s, Kelvin had calculated that the earth could not be more than a few tens or even a few hundred million years old. He clung to his results for decades, indifferent to the fact that they were in complete contradiction to the calculations of geologists and incompatible with the evolution of life according to the processes described by Charles Darwin.

Kelvin had nevertheless gradually refined his assessment, until he proposed, in 1897, a value of between 20 and 400 million years.

But the progress of the radioactive disintegrations, observed by Rutherford and Soddy in Montreal, were to bring an irrefutable argument to the ideas of the Scotsman.

By establishing that radium disintegrated to form, in particular, helium, Rutherford had the idea that the ratio between the quantities of these two elements in a rock could make it possible to determine its age. This idea was exploited by the American chemist and friend of Rutherford named Bertram Borden Boltwood. This allowed Rutherford to present, during a conference at the Royal Society in 1904, results in total contradiction with those of Kelvin. But that evening a surprise guest was waiting for him. Rutherford himself recounted the scene as follows:

"I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in trouble at the last part of my speech dealing with the age of the Earth, where my views conflicted with his. To my relief, Kelvin fell fast asleep, but as I came to the important point, I saw the old bird sit up, open an eye, and cock a baleful glance at me! Then a sudden inspiration came, and I said, "Lord Kelvin had limited the age of the Earth, provided no new source was discovered. That prophetic utterance refers to what we are now considering tonight, radium!" Behold! the old boy beamed upon me."

However, Kelvin never questioned his vision of things, even if new methods developed by Boltwood made it possible to further improve the calculations... and to move further and further away from the results of the "old bird".

This one ended its flight on December 17, 1907. Ernest Rutherford then lost his most faithful opponent.