The German Genius

and Helmholtz, being doctors, came to the science of work through physiology, Helmholtz’s fellow Prussian Rudolf Clausius approached the phenomenon, as did his British and French contemporaries, via the ubiquitous steam engine. Unlike Mayer and Helmholtz, Clausius did succeed in having his first important paper, “On the Moving Force of Heat, and the Laws Regarding the Nature of Heat That Are Deducible Therefrom,” accepted by the Annalen ; it appeared in 1850. 19 Clausius (1822–88) was born in Köslin in Pomerania and was yet another son of a pastor. From the Gymnasium he went to the University of Berlin where he was at first attracted to history (studying under Ranke), but then switched to mathematics and physics. In 1846, two years after graduating at Berlin, Clausius entered Boeckh’s seminar at Halle and worked on explaining the blue color of the sky. The importance of his 1850 paper was immediately recognized and, on the strength of it, he was invited to become a professor at the Royal Artillery and Engineering School in Berlin, later transferring to the chair of mathematical physics at Zurich. 20
    In his famous paper Clausius argued that the production of work resulted not only from a change in the distribution of heat, as Sadi Carnot—the French physicist and military engineer—had argued, but also from the consumption of heat, and that heat could be produced by the “expenditure” of work. “It is quite possible,” he wrote, “that in the production of work…a certain portion of heat may be consumed, and a further portion transmitted from a warm body to a cold one: and both portions may stand in a certain definite relation to the quantity of work produced.” In doing this, he stated two fundamental principles, which would become known as the first and second laws of thermodynamics. 21
    The first law may be illustrated by the way it was later taught to Max Planck, the man who, at the turn of the twentieth century, would build on Clausius’s work. Imagine a worker lifting a heavy stone onto the roof of a house. The stone will remain in position long after it has been left there, storing energy until at some point in the future it falls back to earth. Energy, says the first law, can be neither created nor destroyed. Clausius, however, pointed out in his second law that the first law does not give the total picture. In the example given, energy is expended by the worker as he lifts the stone into place and is dissipated in the effort as heat, which among other things causes the worker to sweat. This dissipation, which Clausius was to term “entropy,” was of fundamental importance, he said, because although it did not disappear from the universe, this energy could never be recovered in its original form. Clausius therefore concluded that the world (and the universe) must always tend toward increasing disorder, must always add to its entropy.
    Clausius never stopped refining his theories of heat, becoming in the process interested in the kinetic theory of gases, in particular the notion that the large-scale properties of gases were a function of the small-scale movements of the particles, or molecules, that comprised the gas. Heat, he came to think, was a function of the motion of such particles—hot gases were made up of fast-moving particles, colder gases of slower particles. 22 Work was understood as “the alteration in some way or another of the arrangement of the constituent molecules of a body.” This idea that heat was a form of motion was not new. The American Benjamin Thompson had observed that heat was produced when a cannon barrel was bored, and in Britain Humphry Davy had likewise noted that ice could be melted by friction. What attracted Clausius’s interest was the exact form of motion that comprised heat. Was it the vibration of the internal particles, was it their “translational” motion as they moved from one position to another, or was it because they rotated on their own axes? 23
    Clausius’s second seminal paper, “On the Kind of Motion That We Call Heat,” was published in the Annalen in 1857, where he argued that the heat of a gas must be made up of all three types of movement and that therefore its total heat ought to be proportional to the sum of these motions. He assumed that the volume occupied by the particles themselves was vanishingly small and that all the particles moved with the same average velocity, which he calculated as being hundreds, if not