Celebrating a scientific pioneer while reflecting on the legacy of their ideas.

If I asked you to name ten famous Rudolphs I suspect that number one would be the fictional reindeer with the very shiny nose and others might include Valentino (the actor), Nureyev (the ballet dancer) and Diesel (the engineer). You might also think of those who shorten their name to Rudi (or Rudy): Dassler (German sneakers manufacturer), Voller (German soccer player), Lewis (lead singer of the Drifters) or Giuliani (enough said). Would there be room in your top ten for Rudolph Clausius?

Clausius has arguably had more impact on your life and career than all the other Rudis put together. He was born 200 years ago in the Prussian city of Köslin, a small port on the Baltic coast which is now named Koszalin and lies halfway between the Polish ports of Szczecin and Gdansk. His father was a school teacher and Pastor and young Rudi was taught by him until he went to high school in Szczecin at the age of 16. This began a thirty year drift in a south-westerly direction across central Europe; firstly to the University of Berlin to study math and physics, then to Halle for his doctorate in atmospheric optics and then, after a brief spell back in Berlin as professor of physics, to the newly founded Federal Institute of Technology (ETH) in Zurich.

While completing his doctoral thesis in Halle he became interested in the work of Carnot and Clapeyron and noted similar interest in England and Scotland, particularly in the work of James Joule and William Rankine. Neither Joule nor Rankine held an academic post at the time and they were conducting their research as hobbies, albeit with an intense passion, alongside their day jobs. Clausius also noted that William Thomson—later known as Lord Kelvin—who was two years his junior, had started to apply more scientific rigor to Joule’s work, but was having doubts about “innumerable other difficulties” which he described as “altogether insurmountable.”

In his first major work on heat and power, published in Germany in 1850 and quickly translated into English to be laid alongside Thomson and Rankine’s publications, Clausius wrote “we ought not to suffer ourselves to be daunted by these difficulties; but that, on the contrary, we must look steadfastly into this theory that calls heat a motion as in this way alone can we arrive at the means of establishing it or refuting it.” He went on to write, “Besides this, I do not imagine that the difficulties are so great as Thomson considers them to be; for although a certain alteration in our way of regarding the subject is necessary, still I find that this is in no case contradicted by proved facts.”

This was the first of nine memoirs published by Clausius over the next fifteen years which led ultimately to his description and naming of a previously unnoticed property of state, entropy, in 1865. Along the way there were some feisty exchanges with Thomson and his followers. There is no doubt, although they were all floating around in the same pool, that Clausius produced a completely fresh concept with entropy (which means “in transformation”) and unlocked the puzzle that was holding all the proto-thermodynamicists back. However, it is less clear whether he fully understood what he had in his hands. It needed the next generation of thinkers, including Josiah Gibbs, Ludwig Boltzmann and James Clerk Maxwell, to take entropy and run with it in the process moving it from the world of physics to chemistry. Gibbs wrote an obituary of Clausius in 1889, concluding that “his true monument lies not on the shelves of libraries, but in the thoughts of men, and in the history of more than one science.”