= William Thomson, 1st Baron Kelvin
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{title2=1824–1907}
{wiki}
= Lord Kelvin
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{synonym}
= William Thomson
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{synonym}
<William Thomson>, later <Lord Kelvin>, distinguished the mechanical equivalence of <heat> from restrictions on cyclic conversion of <heat> into <work>. <Conservation of energy> alone gives $W=Q_h-Q_c$ for a <heat engine>, but does not determine how small the rejected <heat> $Q_c$ can be. His 1851 treatment revised the <caloric> reading of <Carnot's theorem> while retaining a universal limit on reversible engines. In modern absolute-temperature notation, the reversible bound is $W/Q_h\leq1-T_c/T_h$.<Dynamical theory of heat by William Thomson>[Sections 1–14, heat/work equivalence and cyclic-engine restrictions; modern temperature notation]{ref}
A <physicist> whose <thermodynamics> distinguished <conservation of energy> from restrictions on cyclic heat-to-work conversion.
\Image[https://upload.wikimedia.org/wikipedia/commons/a/a0/Lord_Kelvin_photograph.jpg]
{title=William Thomson, Lord Kelvin; photograph credited to Messrs. Dickinson, London; Smithsonian Libraries, via Wikimedia Commons; public domain}
{source=https://commons.wikimedia.org/wiki/File:Lord_Kelvin_photograph.jpg}
{width=250}
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