Clerk Maxwell's electromagnetic theory

The author reviews Maxwell's electromagnetic theory, explaining how it unifies electricity, magnetism, and light and removes earlier ambiguities in electrodynamics and optics. He surveys competing nineteenth-century models and shows how introducing dielectric displacement and the material constants now called dielectric constant and magnetic permeability clarifies open currents, eliminates problematic longitudinal vibrations, and yields correct reflection and refraction formulas. He emphasizes that these constants can be measured by static experiments, describes how the theory fixes the direction of polarization, and acknowledges the debt to earlier experimentalists while noting later extensions and refinements by subsequent researchers.