Clerk Maxwell's electromagnetic theory

In this celebrated Rede Lecture, a leading physicist takes listeners back to the early twentieth‑century turmoil that surrounded electricity, magnetism, and light. He sketches the bewildering landscape of competing ideas—Ampère’s and Grassmann’s laws for currents, Weber’s and Riemann’s speculations on charge interactions, and the rival ether‑density theories of Fresnel and Neumann that struggled to explain reflection and polarization. By laying out these historical puzzles, the speaker sets the stage for the revolutionary insight that would soon emerge.

The core of the talk is James Clerk Maxwell’s bold reformulation of electromagnetism, in which he introduced the concept of dielectric displacement and showed that electric and magnetic fields propagate through a non‑conducting medium as an incompressible fluid. This unification not only eliminated the mysterious “open currents” and longitudinal vibrations that had plagued earlier models, but also revealed light itself as an electromagnetic wave governed by two material constants—dielectric constant and magnetic permeability. Listeners come away with a clear picture of how Maxwell’s theory turned a fragmented field into a coherent, predictive framework that still underpins modern physics.