James Thomson (engineer)

James Thomson (1822 – 1892) was a Scottish engineer and physicist, brother of the more famous William Thomson, 1st Baron Kelvin. He is best known for his theoretical work on thermodynamics, particularly his work on the influence of pressure on the freezing point of water and his analysis of the thermodynamic principles of the steam engine.

Thomson was born in Belfast, Ireland. He initially trained as an engineer, working in his father's engineering practice and later becoming a professor of engineering at Queen's College, Belfast. He later held a professorship in civil engineering at the University of Glasgow.

His theoretical contributions included developing the Thomson effect (also known as the Joule-Thomson effect for liquids) alongside Joule (though his brother William received more credit). This effect describes the temperature change of a real gas or liquid when it is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the environment.

Thomson also made significant contributions to fluid mechanics, particularly in the areas of vortex motion and the flow of water in rivers. He was a meticulous and insightful researcher, whose work had a lasting impact on the fields of thermodynamics and engineering. His publications were collected and published posthumously in Collected Papers in Physics and Engineering.