Unified electrodynamics into 4 fundamental field equations.

Ångström publishes detailed solar atlas, confirming solar hydrogen atmosphere.

Kirchhoff defines an ideal blackbody radiator (a = 1), setting the stage for quantum mechanics.

Loschmidt calculates molecular diameter (1 nm) and Avogadro's constant from kinetic gas theory.

Maxwell demonstrates three-color trichromatic color synthesis at the Royal Institution.

Maxwell and Boltzmann formalize statistical gas distribution, incorporating thermal energy states.

Cannizzaro presents Avogadro's hypothesis at Karlsruhe, standardizing atomic masses and molecular formulas.

Kirchhoff and Bunsen invent chemical spectrum analysis, discovering cesium (1860) and rubidium (1861).

Kirchhoff proves that emissivity equals absorptivity (e_lambda = a_lambda), establishing thermal radiation universality.