A carte de visite photographic (CDV) portrait of Scottish physicist James Clerk Maxwell (1831–1879), best known for his formulation of the classical theory of electromagnetic radiation, bringing together electricity, magnetism and light in a single framework.  The photograph is by Fergus of Greenock, a Scottish photographer of the period, and shows Maxwell in one of his most recognisable later portraits.  Maxwell remains one of the most important figures in the history of science, and photographic portraits of him are sought after by collectors of scientific and historical material.
A good, clear example in keeping with its age.
 
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