Evolution of temperature measurement – beginnings, progress and prospects

Abstract This paper starts by charting the development of temperature measurement from its beginnings with the thermoscope in the late 1500s through to liquid-in-glass and air thermometers in the 1600s and 1700s. The emergence of classical thermodynamics which put thermometry onto a sound physical footing is then briefly described as is the convergence of practical and thermodynamic thermometry in the late 1880s and early 1900s through the use of defined scales, which became the benchmark for reliable thermometry throughout the 20th century and beyond. Finally an outline of the kelvin redefinition in 2019 and its implications is given followed by a discussion of the prospect of driftless practical primary thermometry across a wide temperature range by the 2050s.