What is an achievement of James Clerk Maxwell, a Scottish scientist who helped to develop the concept of coherence?
Coherence (units of measurement):  The concept of coherence was developed in the mid-nineteenth century by, amongst others, Kelvin and James Clerk Maxwell and promoted by the British Association for the Advancement of Science. James Clerk Maxwell:  His most notable achievement was to formulate the classical theory of electromagnetic radiation, bringing together for the first time electricity, magnetism, and light as manifestations of the same phenomenon.
classical theory of electromagnetic radiation