Rudolf Clausius

German physicist

• Born: January 2, 1822; Köslin, Prussia (now Germany)
• Died: August 24, 1888; Bonn, Germany

German physicist Rudolf Clausius is credited with developing the concept of entropy and helping to develop the field of thermodynamics. Clausius’s research also advanced understanding of the kinetic theory of gases and the theory of electrolysis. His work assisted in establishing a general acceptance of theoretical physics within the scientific community.

Primary fields: Physics; mathematics

Specialties: Thermodynamics; atomic and molecular physics

Early Life

Rudolf Julius Emmanuel Clausius (KLOU-zee-uhs) was the sixth son in a family of eighteen children. His father, C. E. G. Clausius, was a Lutheran pastor who opened his own school, serving as its principal. The young Clausius briefly attended his father’s school before completing his schooling in Stettin, Germany (now Szczecin, Poland) in 1840. Clausius then attended the University of Berlin. Although he was interested in history, his career path led him to the study of mathematics and physics. In 1844, he completed his degree and commenced teaching. He received a PhD from the University of Halle in 1848 after defending his dissertation that sought to explain, among other things, why the sky was blue.

Clausius’s early research foreshadowed the prominent themes that became the basis of his life’s work. He made extensive use of mathematics to solve scientific problems. Although some of the problems he tackled were elementary, he also worked on other problems that were considered some of the most vexing scientific dilemmas of the era.

Clausius taught at Berlin’s Friedrich Werner Gymnasium for a total of six years following his 1844 matriculation. During this period, he began research work that would catapult him to the pinnacle of his chosen field. In 1850, he received a physics professorship at the nearby Royal Artillery and Engineering School.

Life’s Work

The work that propelled Clausius to national attention was his first major paper, titled Über die bewegende Kraft der Wärme (“On the motive power of heat”), published in 1850. His path-breaking research contributed to his being offered an academic appointment at the University of Berlin. The article formulated the basis of modern thermodynamics. In it, Clausius further undermined caloric theory, which held that heat is an indestructible fluid transferred from one item to another without being lost.

Clausius linked the mechanical theory of heat with the concept of work. He expanded on the research of scientists credited with formulating the first law of thermodynamics, such as James Joule, as well as scientists whose work is considered a precursor to the second law, such as Nicolas Sadi Carnot. Drawing on Carnot’s theories, Clausius speculated that work initiated by heat requires the consumption of an equivalent amount of heat to produce the desired result. Heat thus produces work, but it is also necessarily destroyed to make that work happen. Clausius further posited that heat flows from hotter to cooler forms of matter. The concerns discussed in his earliest published work would consume Clausius’s research in later years, as he formalized his understanding of what he later called “entropy,” thereby paving the way for the second law of thermodynamics. Clausius’s early research helped to disprove the caloric theory and ushered in the era of theoretical physics.

By 1855, Clausius’s international reputation had garnered him appointments to the Swiss Federal Institute of Technology and the University of Zürich. Over the next few years, the young scientist found himself courted by rival academic institutions offering a variety of lucrative professorships, all of which he turned down. Clausius intended to remain in Zürich until the right offer came along. It was during this period that he married Adelheid Rimpam, with whom he had six children. An ardent German nationalist, Clausius accepted an offer to teach at the University of Würzburg in 1867, a decision that brought him back to his beloved homeland. Two years later, he accepted an appointment to the University of Bonn, where he remained until his death.

During his time in Zürich, Clausius worked extensively on what would become the second law of thermodynamics. Following his critical 1850 publication, Clausius devoted much of his considerable energy to making the second law of thermodynamics understandable to the public and definable by mathematic equations. His 1865 treatise, On Different Forms of the Fundamental Equations of the Mechanical Theory of Heat, introduced the concept of entropy to denote the total heat energy of a system that is not available for work. In effect, entropy serves as the form of energy that is created by any physical process and that is no longer usable. From this basic concept, Clausius postulated that in a closed mechanical system there exists no means to increase energy production. In such a system, he argued, one can also assume that entropy will not decrease.

At the height of his academic prestige, Clausius found himself drawn by his nationalist tendencies to participate in the Franco-Prussian War (1870–71). Too old to be drafted for combat duty, Clausius volunteered in an ambulance corps that removed wounded soldiers from the battlefield, regardless of nationality. During the conflict, he received a leg wound that undermined his mobility and caused him constant pain for the duration of his life. His efforts earned him an Iron Cross from the German government and admission to the Legion of Honor from the French government.

In 1875, his wife died giving birth to the couple’s sixth child. The death of Clausius’s wife affected his career, as he shifted his attention to raising his family. Although he continued teaching, his scholarly contributions diminished. He married Sophie Stack in 1886, with whom he had a child, and he continued working at the University of Bonn until his death in 1888.

Impact

Clausius built upon the research and experimentation of physicists who were either his contemporaries or predecessors. At the same time, he made his own lasting contributions to the field. Nineteenth-century physicists from all over the world were actively engaged in trying to understand the nature of energy and to learn how to make machines more efficient. Clausius played a critical role in this process. Clausius’s contributions not only strengthened the theoretical foundation of the experimentation performed by others (most notably Nicolas Carnot), but also advanced his own theories about thermodynamics that others have in turn built upon.

Clausius is also deemed a critical figure in bolstering the kinetic theory of gases. This theory holds that gas molecules randomly collide and that these collisions with individual molecules and with the sides of the container holding them generate pressure. Previous scientific thought held that a system’s energy derived from the force that repelled molecules from each other. The kinetic theory would later be used as evidence of the existence of atoms. Furthermore, Clausius is credited for key advances in the theory of electrolysis, especially in his postulate that electrolyte molecules are composed of substituting atoms that are guided but not forced into the interchange by electric energy.

Bibliography

Clausius, Rudolf, J. E. The Mechanical Theory of Heat. Trans. Walter R. Browne. Whitefish: Kessinger, 2010. Print. Reprint of Clausius’s widely acclaimed 1879 work, outlining his complete understanding of the laws of thermodynamics, which had been the focal point of his research for decades.

Guillen, Michael. Five Equations that Changed the World: The Power and Poetry of Mathematics. New York: Hyperion, 1996. Print. Devotes a chapter to Clausius’s mathematical formula. Explains the second law of thermodynamics.

Harman, Peter M. Energy, Force, and Matter: The Conceptual Development of Nineteenth-Century Physics. New York: Cambridge UP, 1982. Print. Organizes the disparate streams of often-contradictory scientific thought in the nineteenth century. Clausius figures prominently in the account.

Von Baeyer, Hans Christian. Warmth Disperses and Time Passes: The History of Heat. New York: Modern Library, 1999. Print. Examines the evolution of humanity’s understanding of the concept of heat. Discusses the central figures in the emergence of thermodynamics, including notes on the life and work of Clausius.

Watson, Peter. The German Genius: Europe’s Third Renaissance, the Second Scientific Revolution, and the Twentieth Century. New York: Harper Perennial, 2011. Print. Places Clausius’s achievements within the context of German scientific experimentation. Describes the scientific environment that fostered his creative genius.