When did William Thomson publicly endorse James Prescott Joule’s theory of heat?

William Thomson, later known as Lord Kelvin, first gave public recognition and a cautious endorsement of James Prescott Joule’s theory regarding the interconvertibility of heat and motion in 1851.1

He provided this endorsement in his major mathematical treatise titled "On the Dynamical Theory of Heat," which also included his version of the second law of thermodynamics. Prior to this, Thomson had first encountered Joule's theory at a meeting of the British Association for the Advancement of Science in 1847, where he initially reserved judgment while remaining open-minded about the implications of the new theory.1