Historical context
James Prescott Joule (1818–1889) was a Manchester brewer, not an academic, but his obsession with measurement precision led him to build the most celebrated apparatus in thermodynamics: a system of rotating paddles driven by falling weights stirred water in an insulated container. By measuring the heating of the water with extreme care, he showed that a fixed amount of mechanical work always produces the same amount of heat: (Simonyi 2012, ch. 4).
Joule’s experiment is the direct experimental proof of the mechanical equivalent of heat: the work of the falling weights, a purely mechanical process, is converted entirely into the internal energy of the water, measured by its rise in temperature. It is the experimental backbone of the first law.
Joule’s first report was met with complete indifference, except from one enthusiastic young man, William Thomson, the future Lord Kelvin. Julius Robert von Mayer had had the same insight in 1842, noticing that the venous blood of tropical sailors was redder (a sign that in a hot climate the body consumes less oxygen to keep its temperature), but his paper was rejected by the Annalen der Physik for being too philosophical in style (Simonyi 2012, pp. 376–377).
The story is a lesson: a correct idea can go unheard for years until it finds both the precision measurement (Joule) and the authoritative champion (Kelvin). See also Riferimenti bibliografici.
Links
Topics: Thermodynamics Concepts: First law of thermodynamics
Related exercises: Nitrogen heated in a rigid cylinder · Same temperature, different heat · Raising a vertical piston