To the Editors:
"Great men," wrote science philosopher Karl Popper, "often make great mistakes." The great Lord Kelvin made more mistakes than just the Earth's age ("Kelvin, Perry and the Age of the Earth," July-August 2007). Another one, less known perhaps, made near the end of his life (after tenure as Royal Society secretary) was that the Sun was isotropic (that its magnetic waves are issued in all directions, all of the time). This turned out not to be the case, either observationally or mathematically. Mathematically, he wrongly assumed that the field strength of the magnetic waves decreased as an inverse of the distance to the cubic power. It is actually less rapid and perhaps an inverse of distance squared. Less is known about how he responded to solar observations that falsified isotropic behavior.
An early sally against Kelvin in this particular error was delivered by the mathematician Sydney Chapman. Kelvin, he said, did not make the important distinction between worldwide and local changes in the geomagnetic field when making his energy assumptions.
Kelvin's insistence on the Sun's isotropic behavior went contra to the Royal Observatory at Greenwich's solar section, formerly led in a pioneering yet methodical manner by E. Walter Maunder for over 20 observation-filled, data recording years. Two years before Kelvin died, Maunder pointed out where the master went wrong, and resolved what Kelvin had called the "fifty year's difficulty" (of Edward Sabine, about magnetic storms) in an address before the Royal Astronomical Society in 1905. A lot of booing was promised due to his challenge, but Maunder answered his critics well, regarding both observations and calculations. As early as the first decade of the 20th century, Maunder coordinated many researchers and observations to find that magnetic storms do come from the Sun, and that its magnetic activity is not from the entire solar surface but from rather specific areas and along thin lines. He also proved that these storms strike Earth and, as had already been known by Sabine and Richard Carrington, they disrupt telegraph communications. Maunder suggested that the math be done in obedience to the observations instead of in obedience to an isotropic assumption.
Kelvin never replied to Maunder's address and it is not clear if he was even aware of Maunder's speech. Lord Kelvin's mistake still showed up in textbooks 40 years after he made his claim. Some say it held back solar science research in some crucial ways for years. In more modern times Eugene N. Parker, delineator of the solar wind, said that Kelvin "ignored the suggestion that the geomagnetic variations might be the result of a beam of corpuscular radiation" (which today is often called plasma).
Great men make great mistakes. It is perhaps inevitable: so much good comes with some bad. Lest we make much of any person's catapulting to fame and, hence, become target for invective, Kelvin was great, nonetheless. He arguably was the father of electromagnetism, giving Maxwell his basis for further study and research. Like all the true "greats" (such as Newton and Galileo) Kelvin was inventor, theorist and pragmatist all in one. An invention of his made the transatlantic telephone cable work: American and English stock markets became connected in an instant. Being one of the few ranking physicists then alive who was able to understand what Nikola Tesla was talking about in terms of alternating-current motors, Kelvin applauded it and told Westinghouse to invest in it. From Niagara Falls' distance, Tesla and Westinghouse lit up New York City. Alternating current has been economically lighting the world ever since.
Ironically enough, Tesla's inspiration for AC motors came, he claimed, from a vision he had looking into the setting Sun.
For these two acts alone William Thomson, First Baron of Kelvin, left the world a more wealthy and comfortable place than he entered. We should forgive him his numerous errors in theory because of the support he gave underdogs such as Tesla.
Thanks must always go to all who challenge accepted wisdom for the better. They may not be listened to at first. But eventually, what they point out will be understood by all.
Steven H. Yaskell