 In his 1851 paper, Thomson was willing to go no further than a compromise and declared "the whole theory of the motive power of heat is founded on  two  propositions, due respectively to Joule, and to Carnot and Clausius".As soon as Joule read the paper he wrote to Thomson with his comments and questions.Thus began a fruitful, though largely epistolary, collaboration between the two men, Joule conducting experiments, Thomson analysing the results and suggesting further experiments.