How did William Thomson help develop the dynamical theory of heat?

William Thomson, Baron Kelvin, played a pivotal role in the development of the dynamical theory of heat by synthesizing disparate physical concepts into a unified framework. His contributions were instrumental in transitioning scientific understanding away from the then-prevalent "caloric" theory, which viewed heat as an imponderable fluid.12

Key aspects of his involvement include:

• Endorsement of Joule’s Theory: In 1847, Thomson encountered James Prescott Joule’s theory regarding the interconvertibility of heat and mechanical motion. Although initially skeptical, Thomson eventually recognized the validity of Joule’s ideas, which contradicted the caloric theory.2
• Mathematical Treatise: In 1851, Thomson published his landmark essay, "On the Dynamical Theory of Heat." This work provided a cautious but significant endorsement of Joule’s theory and integrated it into a broader scientific context.2
• Formulation of the Second Law: Within this same 1851 essay, Thomson formulated his version of the second law of thermodynamics, which established that it is impossible to convert heat entirely into work in a cyclic process.23
• Synthesis of Energy: Thomson applied mathematical analogies—such as those he developed for heat flow and electricity—to demonstrate that various physical phenomena were energy-related, ultimately helping to establish the modern dynamical theory of heat.12