Gustave Adolphe Hirn (21.08.1815-14.01.1890) was a French physicist and engineer and a corresponding member of the Paris Academy of Sciences. He was born in Logelbach (Alsace). He was educated at home and studied physics and chemistry on his own. He worked as an engineer in Logelbach and was technical director of a weaving mill.
His work concerned thermodynamics and heat engineering. He studied the properties of gases and of water vapour, in particular saturated and superheated vapour, and the work done by steam in steam engines. He carried out (1855—58) original studies to determine the mechanical equivalent of heat in experiments on the conversion of heat into work performed in a steam engine, obtaining a value of the mechanical equivalent of heat equal to 413 kgf·m/kcal. These experiments played a large part in the establishment of the mechanical theory of heat.
He carried out (in the 1850s) a large body of work on the experimental study of the operation of steam engines and on their improvement. He proved (1857) the advantage of using superheated steam in them rather than saturated steam, pointed out the need to take into account the heat exchange between the steam and the cylinder walls, which affects the consumption of steam, and developed a theory of this phenomenon and the method of the so-called calorimetric analysis of steam engines, which makes it possible to determine the amount of heat absorbed or given up by the wall during a cycle. His book “The Mechanical Theory of Heat” (1854; 1876, 3rd ed.) is widely known. His research also concerned climatology and meteorology.
A member of the St Petersburg Academy of Sciences (1866) and of the Accademia dei Lincei (1888).